title: Love Aaj Kal (2020 film)

text: Back to the present day, Veer drops her for an interview at the office of the Mehta Group, and they slowly begin their relationship. Raj, who is affiliated with the Mehta Group, is an ex-medical student who ran away from Udaipur and now owns several restaurants in Delhi, including the café at which Zoe hangs out very often. Raj, who is good friends with Zoe, tells her the story of his childhood sweetheart, Leena, implying that he is a grown-up Raghu. He tells her that he used to behave with Leena just as Veer acts with Zoe, recites his childhood memories with Leena to Zoe, and tells her how he asked Leena for a dance together.


title: Love Aaj Kal (2020 film)

text: Again in a flashback, it is seen that Raghu and Leena used to meet each other secretly and how Raghu left everything for Leena and moved for her to Delhi, discontinuing his studies to be with Leena. Later, Zoe walks in on Raj and a woman, assuming she is Leena but realizes it's not the case. Raj now reveals that he left Leena for his big town fantasies. Her mother convinces Zoe that she can't possibly have both her love and career together. She goes to meet Veer's parents but leaves crying. Veer relays to Raj what Zoe did, and Raj, convinced that he influenced Zoe towards behaving this way, responds by getting her the job.


title: Love Aaj Kal (2020 film)

text: Some days later, Zoe sees Veer with another girl. Heartbroken, she hangs out with multiple people but doesn't happen to like any of them. She goes to a bar with a guy and gets drunk, but he refuses to drop her at her home. Veer picks her and drops her at her house. He says that he can't enter a relationship of compromises with Zoe and breaks up with her. The next day he informs her about a new job in the Himalayas and is leaving for two years, explaining that he has as much right to be focused on his career as does she, and bids her goodbye. Zoe gets a proposal from the Mehta family for marriage, but she refuses. When Zoe meets Raghu, he tells her that he met Leena one last time, when he realized he lost the person he was before with Leena and finds that she is pregnant. He leaves from there, gets into a cab, and goes to the airport. He adds that he still misses Leena but is helpless now. He starts crying, and Zoe comforts him. Raghu tells her that she shouldn't make the same mistake he made. Zoe leaves for the Himalayas to reunite with Veer. She sees Veer sleeping outside. She goes and lays on top of him. She says that she won't balance between love & work ever, but still, she wanted to be with him. Veer asks whether she will leap with him, to which she agrees, and they reunite.


title: Love Aaj Kal (2020 film)

text: On 17 January 2019, it was reported that Imtiaz Ali was considering his next venture (a romantic film) with Sara Ali Khan and Kartik Aaryan. On 1 March 2019, it was confirmed that the pair has been teamed up in a directorial venture of Ali and the filming will start in Delhi.


title: Love Aaj Kal (2020 film)

text: The principal photography of the film began in the second week of March 2019, with Aaryan sharing a picture of Khan and him from the sets. Khan also shared the picture on her social media account. The first schedule of the film was wrapped on 25 March 2019. To inform about the conclusion of the schedule, Khan posted a video on her Instagram to celebrate. The 20-day second schedule of the film began on 10 April in Udaipur. Filming was completed on 1 July 2019, after the final 66 days of shooting in Himachal Pradesh.


title: Love Aaj Kal (2020 film)

text: The film was released in India on 14 February 2020. The film was made available for streaming on Netflix and JioCinema on 28 April 2020. Love Aaj Kal's television premiere was occurred on Star Plus.


title: Love Aaj Kal (2020 film)

text: The film's songs are composed by Pritam, with lyrics written by Irshad Kamil and the album was well received by the audiences. Every soundtrack in the album has its own flavour and emotion which was used as the narrative.


title: Love Aaj Kal (2020 film)

text: The film score was composed by Ishaan Chhabra. The film variant of the reprise version of "Shayad" is sung by Jubin Nautiyal, released April 2021.


title: Love Aaj Kal (2020 film)

text: In the film credits the song "Aur Tanha" is entitled "Tanna Karta" and song "Shayad" sung by Arijit Singh for Pre-Interval and Jubin Nautiyal for Post-Interval.


title: Love Aaj Kal (2020 film)

text: The song "Shayad (Aaj Kal)" also sung by Pritam featuring Arijit Singh by title "Shayad (Aaj Kal) Lockdown Version" uploaded on Pritam's YouTube Channel. All songs under label Sony Music India.


title: Love Aaj Kal (2020 film)

text: The film received mixed reviews from critics and audiences. Ronak Kotecha of the "Times of India" rated the film 3/5, stating that "the flashback story is interrupted way too many times to accommodate the film's non-linear narrative." Baradwaj Rangan of "Film Companion" wrote "Despite its many imperfections, if there's one thing that gladdened me about "LAK"-2020, it's that IA hasn't lost his ability to write those great scenes we want (and expect) from him."


title: Love Aaj Kal (2020 film)

text: "Love Aaj Kal" earned nett at the domestic box office on its opening day. On the second day, the film collected . On the third day, the film collected , taking its total opening weekend collection to nett.


title: Love Aaj Kal (2020 film)

text: , with a gross of in India and in overseas, the film has a worldwide gross collection of ₹52.6 crore.


title: Ohio River

text: The Ohio River is a long river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing southwesterly from western Pennsylvania to its mouth on the Mississippi River at the southern tip of Illinois. It is the third largest river by discharge volume in the United States and the largest tributary by volume of the north-south flowing Mississippi River that divides the eastern from western United States. It is also the 6th oldest river on the North American continent. The river flows through or along the border of six states, and its drainage basin includes parts of 14 states. Through its largest tributary, the Tennessee River, the basin includes several states of the southeastern U.S. It is the source of drinking water for five million people.


title: Ohio River

text: The lower Ohio River just below Louisville is obstructed by rapids known as the Falls of the Ohio where the elevation falls in restricting larger commercial navigation, although in the 18th and early 19th century its three deepest channels could be traversed by a wide variety of craft then in use. Completion of the Louisville and Portland Canal in 1830 (and later the McAlpine Locks and Dam), bypassing the rapids, allowed even larger commercial and modern navigation from the Forks of the Ohio at Pittsburgh to the Port of New Orleans at the mouth of the Mississippi on the Gulf of Mexico.


title: Ohio River

text: The name "Ohio" comes from the Seneca, ,  "Good River". In his "Notes on the State of Virginia" published in 1781–82, Thomas Jefferson stated: "The Ohio is the most beautiful river on earth. Its current gentle, waters clear, and bosom smooth and unbroken by rocks and rapids, a single instance only excepted" (though Jefferson himself had not seen the Ohio) In the late 18th century, the river was the southern boundary of the Northwest Territory. It became a primary transportation route for pioneers during the westward expansion of the early U.S. Today, the Ohio River is one of the most polluted rivers in the United States.


title: Ohio River

text: The river is sometimes considered as the western extension of the Mason–Dixon Line that divided Pennsylvania from Maryland, and thus part of the border between free and slave territory, and between the Northern and Southern United States or Upper South. Where the river was narrow, it was crossed by thousands of slaves escaping to the North for freedom; many were helped by free blacks and whites of the Underground Railroad resistance movement.


title: Ohio River

text: The Ohio River is a climatic transition area, as its water runs along the periphery of the humid subtropical and humid continental climate areas. It is inhabited by fauna and flora of both climates. In winter, it regularly freezes over at Pittsburgh but rarely farther south toward Cincinnati and Louisville. Further down the river in places like Paducah and Owensboro, Kentucky, closer to its confluence with the Mississippi, the Ohio is ice-free year-round.


title: Ohio River

text: The name "Ohio" comes from the Seneca language (an Iroquoian language), (roughly pronounced oh-hee-yoh, with the vowel in "hee" held longer), a proper name derived from ("good river"), therefore literally translating to "Good River". "Great river" and "large creek" have also been given as translations.


title: Ohio River

text: Native Americans, including the Lenni Lenape and Iroquois, considered the Ohio and Allegheny rivers as the same, as is suggested by a New York State road sign on Interstate 86 that refers to the Allegheny River also as . Similarly, the Geographic Names Information System lists "O-hee-yo" and "O-hi-o" as variant names for the Allegheny.


title: Ohio River

text: An earlier Miami-Illinois language name was also applied to the Ohio River, ("river of the Mosopelea" tribe). Shortened in the Shawnee language to , or , the name evolved through variant forms such as "Polesipi", "Peleson", "Pele Sipi" and "Pere Sipi", and eventually stabilized to the variant spellings "Pelisipi", "Pelisippi" and "Pellissippi". Originally applied just to the Ohio River, the "Pelisipi" name later was variously applied back and forth between the Ohio River and the Clinch River in Virginia and Tennessee. In his original draft of the Land Ordinance of 1784, Thomas Jefferson proposed a new state called "Pelisipia", to the south of the Ohio River, which would have included parts of present-day Eastern Kentucky, Virginia and West Virginia.


title: Ohio River

text: The river had great significance in the history of the Native Americans, as numerous prehistoric and historic civilizations formed along its valley. For thousands of years, Native Americans used the river as a major transportation and trading route. Its waters connected communities.


title: Ohio River

text: In the five centuries before European colonization, the Mississippian culture built numerous regional chiefdoms and major earthwork mounds in the Ohio Valley like the Angel Mounds near Evansville, Indiana as well as in the Mississippi Valley and the Southeast. The historic Osage, Omaha, Ponca, and Kaw peoples lived in the Ohio Valley. Under pressure over the fur trade from the Iroquois nations to the northeast, they migrated west of the Mississippi River in the 17th century to the territory now defined as Missouri, Arkansas, and Oklahoma.


title: Ohio River

text: Several accounts exist of the discovery and traversal of the Ohio River by Europeans in the latter half of the 17th century: Virginian colonist Abraham Wood's trans-Appalachian expeditions between 1654 and 1664; Frenchman Robert de La Salle's putative Ohio expedition of 1669; and two expeditions of Virginians sponsored by Colonel Wood: the Batts and Fallam expedition of 1671, and the Needham and Arthur expedition of 1673-74. The first known European to traverse the length of the river, from the headwaters of the Allegheny to its mouth on the Mississippi, was a Dutchman from New York, Arnout Viele, in 1692.


title: Ohio River

text: In 1749, the Ohio Company was established in the Thirteen Colonies to settle and trade in the Ohio River region. Exploration of the territory and trade with the Indians in the region near the Forks brought white colonists from both Pennsylvania and Virginia across the mountains, and both colonies claimed the territory. The movement across the Allegheny Mountains of Anglo-American settlers and the claims of the area near modern-day Pittsburgh led to conflict with the French, who had forts in the Ohio River Valley. This conflict was called the French and Indian War, and would merge into the global Anglo-French struggle, the Seven Years' War. In 1763, following its defeat in the war, France ceded its area east of the Mississippi River to Britain and its area west of the Mississippi River to Spain in the 1763 Treaty of Paris.


title: Ohio River

text: The 1768 Treaty of Fort Stanwix with several tribes opened Kentucky to colonial settlement and established the Ohio River as a southern boundary for American Indian territory. In 1774 the Quebec Act restored the land east of the Mississippi River and north of the Ohio River to Quebec, in effect making the Ohio the southern boundary of Canada. This appeased French Canadians in Quebec but angered the colonists of the Thirteen Colonies. Lord Dunmore's War south of the Ohio river also contributed to cession of land north to Quebec to prevent colonial expansion onto Native American territory. During the Revolutionary War. in 1776 the British military engineer John Montrésor created a map of the river showing the strategic location of Fort Pitt, including specific navigational information about the Ohio River's rapids and tributaries in that area. However, the 1783 Treaty of Paris gave the entire Ohio Valley to the United States, and numerous white settlers entered the region.


title: Ohio River

text: The economic connection of the Ohio Country to the East was significantly increased in 1818 when the National Road being built westward from Cumberland, Maryland, reached Wheeling, Virginia, (now West Virginia), providing an easier overland connection from the Potomac River to the Ohio River. The Wheeling Suspension Bridge was built over the river at Wheeling from 1847 to 1849, making the trip west easier. For a brief time, until 1851, it was the world's largest suspension bridge. The bridge survived the American Civil War, after having been improved in 1859. It was renovated again in 1872, and remains in use as the oldest vehicular suspension bridge in the U.S.


title: Ohio River

text: Louisville was founded in 1779 at the only major natural navigational barrier on the river, the Falls of the Ohio. The Falls were a series of rapids where the river dropped in a stretch of about . In this area, the river flowed over hard, fossil-rich beds of limestone. The first locks on the river the Louisville and Portland Canal were built between 1825 and 1830 to circumnavigate the falls. Fears that Louisville's transshipment industry would collapse proved ill-founded: but the increasing size of steamships and barges on the river meant that the outdated locks could serve only the smallest vessels until well after the Civil War when improvements were made. The U.S. Army Corps of Engineers improvements were expanded again in the 1960s, forming the present-day McAlpine Locks and Dam.


title: Ohio River

text: During the nineteenth century, emigrants from Virginia, North Carolina and Kentucky traveled by the river and settled along its northern bank. Known as butternuts, they formed the dominant culture in the southern portions of Ohio, Indiana and Illinois with a society that was primarily Southern in culture. Largely devoted to agricultural pursuits, they shipped much of their produce along the river to ports such as Cincinnati.


title: Ohio River

text: Because the Ohio River flowed westward, it became a convenient means of westward movement by pioneers traveling from western Pennsylvania. After reaching the mouth of the Ohio, settlers would travel north on the Mississippi River to St. Louis, Missouri. There, some continued on up the Missouri River, some up the Mississippi, and some farther west over land routes. In the early 19th century, river pirates such as Samuel Mason, operating out of Cave-In-Rock, Illinois, waylaid travelers on their way down the river. They killed travelers, stealing their goods and scuttling their boats. The folktales about Mike Fink recall the keelboats used for commerce in the early days of American settlement. The Ohio River boatmen inspired performer Dan Emmett, who in 1843 wrote the song "The Boatman's Dance".


title: Ohio River

text: Trading boats and ships traveled south on the Mississippi to New Orleans, and sometimes beyond to the Gulf of Mexico and other ports in the Americas and Europe. This provided a much-needed export route for goods from the west since the trek east over the Appalachian Mountains was long and arduous. The need for access to the port of New Orleans by settlers in the Ohio Valley is one of the factors that led to the United States' Louisiana Purchase in 1803.


title: Ohio River

text: Because the river is the southern border of Ohio, Indiana, and Illinois, it was part of the border between free states and slave states in the years before the American Civil War. The expression "sold down the river" originated as a lament of Upper South slaves, especially from Kentucky, who were shipped via the Ohio and Mississippi to cotton and sugar plantations in the Deep South. Changes in crops cultivated in the Upper South resulted in slaves available to be sold to the South, where the expansion of cotton plantations was doing very well. Invention of the cotton gin made cultivation of short-staple cotton profitable throughout the Black Belt of this region.


title: Ohio River

text: Before and during the Civil War, the Ohio River was called the "River Jordan" by slaves crossing it to escape to freedom in the North via the Underground Railroad. More escaping slaves, estimated in the thousands, made their perilous journey north to freedom across the Ohio River than anywhere else across the north-south frontier. Harriet Beecher Stowe's "Uncle Tom's Cabin", the bestselling novel that fueled abolitionist work, was the best known of the anti-slavery novels that portrayed such escapes across the Ohio. The times have been expressed by 20th-century novelists as well, such as the Nobel Prize-winning Toni Morrison, whose novel "Beloved" was adapted as a film of the same name. She also composed the libretto for the opera "Margaret Garner" (2005), based on the life and trial of an enslaved woman who escaped with her family across the river.


title: Ohio River

text: The colonial charter for Virginia defined its territory as extending to the north shore of the Ohio, so that the riverbed was "owned" by Virginia. Where the river serves as a boundary between states today, Congress designated the entire river to belong to the states on the east and south, i.e., West Virginia and Kentucky at the time of admission to the Union, that were divided from Virginia. Thus Wheeling Island, the largest inhabited island in the Ohio River, belongs to West Virginia, although it is closer to the Ohio shore than to the West Virginia shore. Kentucky sued the state of Indiana in the early 1980s because of their construction of the never-completed Marble Hill Nuclear Power Plant in Indiana, which would have discharged its waste water into the river. This would have adversely affected Kentucky's water supplies.


title: Ohio River

text: The U.S. Supreme Court held that Kentucky's jurisdiction (and, implicitly, that of West Virginia) extended only to the low-water mark of 1793 (important because the river has been extensively dammed for navigation so that the present river bank is north of the old low-water mark.) Similarly, in the 1990s, Kentucky challenged Illinois's right to collect taxes on a riverboat casino docked in Metropolis, citing its own control of the entire river. A private casino riverboat that docked in Evansville, Indiana, on the Ohio River opened about the same time. Although such boats cruised on the Ohio River in an oval pattern up and down, the state of Kentucky soon protested. Other states had to limit their cruises to going forward, then reversing and going backward on the Indiana shore only. Both Illinois and Indiana have long since changed their laws to allow riverboat casinos to be permanently docked, with Illinois changing in 1999 and Indiana in 2002.


title: Ohio River

text: The Silver Bridge at Point Pleasant, West Virginia collapsed into the river on December 15, 1967. The collapse killed 46 people who had been crossing when the bridge failed. The bridge had been built in 1929, and by 1967 was carrying too heavy a load for its design. The bridge was rebuilt about one mile downstream and in service as the Silver Memorial Bridge in 1969.


title: Ohio River

text: In the early 1980s, the Falls of the Ohio National Wildlife Conservation Area was established at Clarksville, Indiana.


title: Ohio River

text: The Ohio River as a whole is ranked as the most polluted river in the United States, based on 2009 and 2010 data. The more industrial and regional West Virginia/Pennsylvania tributary, the Monongahela River, ranked 17th for water pollution, behind 16 other American rivers. The Ohio again ranked as the most polluted in 2013, and has been the most polluted river since at least 2001, according to the Ohio River Valley Water Sanitation Commission (ORSANCO). The Commission found that 92% of toxic discharges were nitrates, including farm runoff and waste water from industrial processes such as steel production. The Commission also noted mercury pollution as an ongoing concern, citing a 500% increase in mercury discharges between 2007 and 2013.


title: Ohio River

text: For several decades beginning in the 1950s, the Ohio River was polluted with hundreds of thousands of pounds of PFOA, a fluoride-based chemical used in making teflon, among other things, by the DuPont chemical company from an outflow pipe at its Parkersburg, West Virginia, facility.


title: Ohio River

text: The Ohio River is extensively industrialized and populated. Regular barge traffic carries cargoes of oil, steel and other industrial goods produced in the region. Major cities located along the northern and southern banks of the river include Pittsburgh, Pennsylvania; Louisville, Kentucky; Evansville, Indiana; and Cincinnati, Ohio.


title: Ohio River

text: The combined Allegheny-Ohio river is long and carries the largest volume of water of any tributary of the Mississippi. The Indians and early European explorers and settlers of the region often considered the Allegheny to be part of the Ohio. The forks (the confluence of the Allegheny and Monongahela rivers at what is now Pittsburgh) were considered a strategic military location by colonial French and British, and later independent American military authorities.


title: Ohio River

text: The Ohio River is formed by the confluence of the Allegheny and Monongahela rivers at what is now Point State Park in Pittsburgh, Pennsylvania. From there, it flows northwest through Allegheny and Beaver counties, before making an abrupt turn to the south-southwest at the West Virginia–Ohio–Pennsylvania triple-state line (near East Liverpool, Ohio; Chester, West Virginia; and Ohioville, Pennsylvania). From there, it forms the border between West Virginia and Ohio, upstream of Wheeling, West Virginia.


title: Ohio River

text: The river follows a roughly southwest and then west-northwest course until Cincinnati, before bending to a west-southwest course for most of the remainder of its length. The course forms the northern borders of West Virginia and Kentucky; and the southern borders of Ohio, Indiana and Illinois, until it joins the Mississippi River at the city of Cairo, Illinois. Where the Ohio joins the Mississippi is the lowest elevation in the state of Illinois, at .


title: Ohio River

text: The Mississippi River flows to the Gulf of Mexico on the Atlantic Ocean. Among rivers wholly or mostly in the United States, the Ohio is the second largest by discharge volume and the tenth longest and has the eighth largest drainage basin. It serves to separate the Midwestern Great Lakes states from the Upper South states, which were historically border states in the Civil War.


title: Ohio River

text: The Ohio River is a left (east) and the largest tributary by volume of the Mississippi River in the United States. At the confluence, the Ohio is considerably bigger than the Mississippi, measured by long-term mean discharge. The Ohio River at Cairo is 281,500 cu ft/s (7,960 m/s); and the Mississippi River at Thebes, Illinois, which is upstream of the confluence, is 208,200 cu ft/s (5,897 m/s). The Ohio River flow is greater than that of the Mississippi River, so hydrologically the Ohio River is the main stream of the river system.


title: Ohio River

text: The Ohio River is a naturally shallow river that was artificially deepened by a series of dams. The natural depth of the river varied from about . The dams raise the water level and have turned the river largely into a series of reservoirs, eliminating shallow stretches and allowing for commercial navigation. From its origin to Cincinnati, the average depth is approximately . The largest immediate drop in water level is below the McAlpine Locks and Dam at the Falls of the Ohio at Louisville, Kentucky, where flood stage is reached when the water reaches on the lower gauge. However, the river's deepest point is on the western side of Louisville, Kentucky. From Louisville, the river loses depth very gradually until its confluence with the Mississippi at Cairo, Illinois, where it has an approximate depth of .


title: Ohio River

text: Water levels for the Ohio River from Smithland Lock and Dam upstream to Pittsburgh are predicted daily by the National Oceanic and Atmospheric Administration's Ohio River Forecast Center. The water depth predictions are relative to each local flood plain based upon predicted rainfall in the Ohio River basin in five reports as follows:


title: Ohio River

text: The water levels for the Ohio River from Smithland Lock and Dam to Cairo, Illinois, are predicted by the National Oceanic and Atmospheric Administration's Lower Mississippi River Forecast Center.


title: Ohio River

text: The Ohio's drainage basin covers , encompassing the easternmost regions of the Mississippi Basin. The Ohio drains parts of 14 states in four regions.


title: Ohio River

text: The Ohio River is a climatic transition area, as its water runs along the periphery of the humid continental and humid subtropical climate areas. It is inhabited by fauna and flora of both climates. In winter, it regularly freezes over at Pittsburgh but rarely farther south toward Cincinnati and Louisville. At Paducah, Kentucky, in the south, at the Ohio's confluence with the Tennessee River, it is ice-free year-round.


title: Ohio River

text: In the 21st century, with the 2016 update of climate zones, the humid subtropical zone has stretched across the river, into the southern portions of Ohio, Indiana, and Illinois.


title: Ohio River

text: From a geological standpoint, the Ohio River is young. Before the river was created, large parts of North America were covered by water forming a saltwater lake about 200 miles across and 400 miles in length. The bedrock of the Ohio Valley was mostly set during this time. The river formed on a piecemeal basis beginning between 2.5 and 3 million years ago. The movement of glaciers during the earliest ice ages the contemporary river drainages of the Kanawha, Sandy, Kentucky, Green, Cumberland and Tennessee rivers northward created the Ohio system and the course of early tributaries of the Ohio River, including the Monongahela and the Allegheny rivers, were set. The Teays River was the largest of these rivers. The modern Ohio River flows within segments of the ancient Teays. The ancient rivers were rearranged or consumed.


title: Ohio River

text: The section of the river that runs southwest from Pittsburgh to Cairo, Illinois is around tens of thousands of years old.


title: Ohio River

text: The upper Ohio River formed when one of the glacial lakes overflowed into a south-flowing tributary of the Teays River. Prior to that event, the north-flowing Steubenville River (no longer in existence) ended between New Martinsville and Paden City, West Virginia. The south-flowing Marietta River (no longer in existence) ended between the present-day cities. The overflowing lake carved through the separating hill and connected the rivers. The floodwaters enlarged the small Marietta valley to a size more typical of a large river. The new large river subsequently drained glacial lakes and melting glaciers at the end of the ice ages. The valley grew during and following the ice age. Many small rivers were altered or abandoned after the upper Ohio River formed. Valleys of some abandoned rivers can still be seen on satellite and aerial images of the hills of Ohio and West Virginia between Marietta, Ohio, and Huntington, West Virginia.


title: Ohio River

text: The middle Ohio River formed in a manner similar to that of the upper Ohio River. A north-flowing river was temporarily dammed by natural forces southwest of present-day Louisville, creating a large lake until the dam burst. A new route was carved to the Mississippi. Eventually, the upper and middle sections combined to form what is essentially the modern Ohio River.


title: Ohio River

text: Along the banks of the Ohio are some of the largest cities in their respective states: Pittsburgh, the third largest city on the river and second-largest city in Pennsylvania; Cincinnati, the third-largest city in Ohio; Louisville, the largest city on the river and in Kentucky; Evansville, the third-largest city in Indiana; Owensboro, the fourth-largest city in Kentucky; and three of the five largest cities in West Virginia—Huntington (second), Parkersburg (fourth), and Wheeling (fifth). Only Illinois, among the border states, has no significant cities on the river. There are hundreds of other cities, towns, villages and unincorporated populated places on the river, most of them very small.


title: Ohio River

text: Cities along the Ohio are also among the oldest cities in their respective states and among the oldest cities in the United States west of the Appalachian Mountains (by date of founding): Old Shawneetown, Illinois, 1748; Pittsburgh, Pennsylvania, 1758; Wheeling, West Virginia, 1769; Huntington, West Virginia, 1775; Louisville, Kentucky, 1779; Clarksville, Indiana, 1783; Maysville, Kentucky, 1784; Martin's Ferry, Ohio, 1785; Marietta, Ohio, 1788; Cincinnati, Ohio, 1788; Manchester, Ohio, 1790; Beaver, Pennsylvania, 1792; and Golconda, Illinois, 1798.


title: Ohio River

text: Other cities of interest include Cairo, Illinois, at the confluence of the Ohio with the Mississippi River and the southernmost and westernmost city on the river; and Beaver, Pennsylvania, the site of colonial Fort McIntosh and the northernmost city on the river. It is 548 miles as the crow flies between Cairo and Pittsburgh, but 981 miles by water. Direct water travel over the length of the river is obstructed by the Falls of the Ohio just below Louisville, Kentucky. The Ohio River Scenic Byway follows the Ohio River through Illinois, Indiana and Ohio ending at Steubenville, Ohio, on the river.


title: Ohio River

text: Before there were cities, there were colonial forts. These forts played a dominant role in the French and Indian War, Northwest Indian War and pioneering settlement of Ohio Country. Many cities got their start at or adjacent to the forts. Most were abandoned by 1800. Forts along the Ohio river include Fort Pitt (Pennsylvania), Fort McIntosh (Pennsylvania), Fort Randolph (West Virginia), Fort Henry (West Virginia), Fort Harmar (Ohio), Fort Washington (Ohio), and Fort Nelson (Kentucky). Short-lived, special-purpose forts included Fort Steuben (Ohio), Fort Finney (Indiana), Fort Finney (Ohio) and Fort Gower (Ohio).


title: Krypton

text: Krypton (from 'the hidden one') is a chemical element with the symbol Kr and atomic number 36. It is a colorless, odorless, tasteless noble gas that occurs in trace amounts in the atmosphere and is often used with other rare gases in fluorescent lamps. With rare exceptions, krypton is chemically inert.


title: Krypton

text: Krypton, like the other noble gases, is used in lighting and photography. Krypton light has many spectral lines, and krypton plasma is useful in bright, high-powered gas lasers (krypton ion and excimer lasers), each of which resonates and amplifies a single spectral line. Krypton fluoride also makes a useful laser medium. From 1960 to 1983, the official definition of meter was based on the wavelength of one spectral line of krypton-86, because of the high power and relative ease of operation of krypton discharge tubes.


title: Krypton

text: Krypton was discovered in Britain in 1898 by William Ramsay, a Scottish chemist, and Morris Travers, an English chemist, in residue left from evaporating nearly all components of liquid air. Neon was discovered by a similar procedure by the same workers just a few weeks later. William Ramsay was awarded the 1904 Nobel Prize in Chemistry for discovery of a series of noble gases, including krypton.


title: Krypton

text: In 1960, the International Bureau of Weights and Measures defined the meter as 1,650,763.73 wavelengths of light emitted in the vacuum corresponding to the transition between the levels 2p and 5d of krypton-86 isotope . This agreement replaced the 1889 international prototype meter, which was a metal bar located in Sèvres. This also obsoleted the 1927 definition of the ångström based on the red cadmium spectral line, replacing it with 1 Å = 10 m. The krypton-86 definition lasted until the October 1983 conference, which redefined the meter as the distance that light travels in vacuum during 1/299,792,458 s.


title: Krypton

text: Krypton is characterized by several sharp emission lines (spectral signatures) the strongest being green and yellow. Krypton is one of the products of uranium fission. Solid krypton is white and has a face-centered cubic crystal structure, which is a common property of all noble gases (except helium, which has a hexagonal close-packed crystal structure).


title: Krypton

text: Naturally occurring krypton in Earth's atmosphere is composed of five stable isotopes, plus one isotope (Kr) with such a long half-life (9.2×10 years) that it can be considered stable. (This isotope has the second-longest known half-life among all isotopes for which decay has been observed; it undergoes double electron capture to Se). In addition, about thirty unstable isotopes and isomers are known. Traces of Kr, a cosmogenic nuclide produced by the cosmic ray irradiation of Kr, also occur in nature: this isotope is radioactive with a half-life of 230,000 years. Krypton is highly volatile and does not stay in solution in near-surface water, but Kr has been used for dating old (50,000–800,000 years) groundwater.


title: Krypton

text: Kr is an inert radioactive noble gas with a half-life of 10.76 years. It is produced by the fission of uranium and plutonium, such as in nuclear bomb testing and nuclear reactors. Kr is released during the reprocessing of fuel rods from nuclear reactors. Concentrations at the North Pole are 30% higher than at the South Pole due to convective mixing.


title: Krypton

text: Like the other noble gases, krypton is chemically highly unreactive. The rather restricted chemistry of krypton in the +2 oxidation state parallels that of the neighboring element bromine in the +1 oxidation state; due to the scandide contraction it is difficult to oxidize the 4p elements to their group oxidation states. Until the 1960s no noble gas compounds had been synthesized.


title: Krypton

text: Following the first successful synthesis of xenon compounds in 1962, synthesis of krypton difluoride () was reported in 1963. In the same year, was reported by Grosse, "et al.", but was subsequently shown to be a mistaken identification. Under extreme conditions, krypton reacts with fluorine to form KrF according to the following equation:


title: Krypton

text: Krypton gas in a krypton fluoride laser absorbs energy from a source, causing the krypton to react with fluorine gas, producing the exciplex krypton fluoride, a temporary complex in an excited energy state:


title: Krypton

text: The complex can undergo spontaneous or stimulated emission, reducing its energy state to a metastable, but highly repulsive ground state. The ground state complex quickly dissociates into unbound atoms:


title: Krypton

text: The result is an exciplex laser which radiates energy at 248 nm, near the ultraviolet portion of the spectrum, corresponding with the energy difference between the ground state and the excited state of the complex.


title: Krypton

text: Compounds with krypton bonded to atoms other than fluorine have also been discovered. There are also unverified reports of a barium salt of a krypton oxoacid. ArKr and KrH polyatomic ions have been investigated and there is evidence for KrXe or KrXe.


title: Krypton

text: The reaction of with produces an unstable compound, , that contains a krypton-oxygen bond. A krypton-nitrogen bond is found in the cation [HC≡N–Kr–F], produced by the reaction of with [HC≡NH][AsF] below −50 °C. HKrCN and HKrC≡CH (krypton hydride-cyanide and hydrokryptoacetylene) were reported to be stable up to 40 K.


title: Krypton

text: Krypton hydride (Kr(H)) crystals can be grown at pressures above 5 GPa. They have a face-centered cubic structure where krypton octahedra are surrounded by randomly oriented hydrogen molecules.


title: Krypton

text: Earth has retained all of the noble gases that were present at its formation except helium. Krypton's concentration in the atmosphere is about 1 ppm. It can be extracted from liquid air by fractional distillation. The amount of krypton in space is uncertain, because measurement is derived from meteoric activity and solar winds. The first measurements suggest an abundance of krypton in space.


title: Krypton

text: Krypton's multiple emission lines make ionized krypton gas discharges appear whitish, which in turn makes krypton-based bulbs useful in photography as a white light source. Krypton is used in some photographic flashes for high speed photography. Krypton gas is also combined with mercury to make luminous signs that glow with a bright greenish-blue light.


title: Krypton

text: Krypton is mixed with argon in energy efficient fluorescent lamps, reducing the power consumption, but also reducing the light output and raising the cost. Krypton costs about 100 times as much as argon. Krypton (along with xenon) is also used to fill incandescent lamps to reduce filament evaporation and allow higher operating temperatures. A brighter light results with more blue color than conventional incandescent lamps.


title: Krypton

text: Krypton's white discharge is sometimes used as an artistic effect in gas discharge "neon" tubes. Krypton produces much higher light power than neon in the red spectral line region, and for this reason, red lasers for high-power laser light-shows are often krypton lasers with mirrors that select the red spectral line for laser amplification and emission, rather than the more familiar helium-neon variety, which could not achieve the same multi-watt outputs.


title: Krypton

text: The krypton fluoride laser is important in nuclear fusion energy research in confinement experiments. The laser has high beam uniformity, short wavelength, and the spot size can be varied to track an imploding pellet.


title: Krypton

text: In experimental particle physics, liquid krypton is used to construct quasi-homogeneous electromagnetic calorimeters. A notable example is the calorimeter of the NA48 experiment at CERN containing about 27 tonnes of liquid krypton. This usage is rare, since liquid argon is less expensive. The advantage of krypton is a smaller Molière radius of 4.7 cm, which provides excellent spatial resolution with little overlapping. The other parameters relevant for calorimetry are: radiation length of X=4.7 cm, and density of 2.4 g/cm.


title: Krypton

text: The sealed spark gap assemblies in ignition exciters in some older jet engines contain a small amount of krypton-85 to produce consistent ionization levels and uniform operation.


title: Krypton

text: Krypton-83 has application in magnetic resonance imaging (MRI) for imaging airways. In particular, it enables the radiologist to distinguish between hydrophobic and hydrophilic surfaces containing an airway.


title: Krypton

text: Although xenon has potential for use in computed tomography (CT) to assess regional ventilation, its anesthetic properties limit its fraction in the breathing gas to 35%. A breathing mixture of 30% xenon and 30% krypton is comparable in effectiveness for CT to a 40% xenon fraction, while avoiding the unwanted effects of a high partial pressure of xenon gas.


title: Krypton

text: The metastable isotope krypton-81m is used in nuclear medicine for lung ventilation/perfusion scans, where it is inhaled and imaged with a gamma camera.


title: Krypton

text: Krypton-85 in the atmosphere has been used to detect clandestine nuclear fuel reprocessing facilities in North Korea and Pakistan. Those facilities were detected in the early 2000s and were believed to be producing weapons-grade plutonium. Krypton-85 is a medium lived fission product and thus escapes from spent fuel when the cladding is removed. This release is usually not dangerous as krypton is chemically inert and disperses widely in the atmosphere but it can be detected by sufficiently sensitive equipment.


title: Krypton

text: Being lipophilic, Krypton has a significant anaestethic effect (although the mechanism of this phenomenon is still not fully clear, there's good evidence that the two properties are mechanistically related), with narcotic potency seven times greater than air, and breathing an atmosphere of 50% krypton and 50% natural air (as might happen in the locality of a leak) causes narcosis in humans similar to breathing air at four times atmospheric pressure. This is comparable to scuba diving at a depth of and could affect anyone breathing it. At the same time, that mixture would contain only 10% oxygen (rather than the normal 20%) and hypoxia would be a greater concern.


title: Republic of Singapore Air Force

text: The Republic of Singapore Air Force (RSAF) is the aerial service branch of the Singapore Armed Forces (SAF) responsible for controlling and defending the airspace of the country, and providing air support to the Army and Navy. It was established in 1968 as the Singapore Air Defence Command (SADC) before renaming to its current name in 1975. As the most powerful air force in Southeast Asia, the RSAF has undertaken a significant role in Singapore's military defence strategy since its formation.


title: Republic of Singapore Air Force

text: The RSAF has been considered by various analysts as being the most technologically advanced air force in the region, with the ability to successfully continuously act as a strong deterrence from potential hostile nations as well as defending the airspace of the island city-state.


title: Republic of Singapore Air Force

text: As of 2021, the RSAF uses four air bases domestically, most notably at Paya Lebar and Tengah, as well as at civil airports such as Changi and Seletar. It has also overseas detachments in various countries, most notably in Australia, the United States and France. In 2021, the RSAF had a strength of 8,000 active personnel.


title: Republic of Singapore Air Force

text: In January 1968, the United Kingdom, which by this time has lost most of its global prestige especially after the Suez Crisis and was facing major financial difficulties that was greatly exacerbated by the devaluation of the pound, announced the imminent withdrawal of all its troops "East of Suez" by the end of 1971. Prior to then, Singapore had depended heavily on Britain's Royal Air Force (RAF) for its air defence, while the newly established Singapore Armed Forces (SAF) had concentrated its efforts mainly on building up the land-based Singapore Army.


title: Republic of Singapore Air Force

text: The predecessor to the RSAF, the SADC, was formed on 1 September 1968. The SADC's immediate task was to set up the Flying Training School to train pilots. Qualified flying instructors were obtained through Airwork Services Limited, a company specialising in defence services. Basic training for pilots was carried out using two Cessna light aircraft hired from the Singapore Flying Club. The SADC also enlisted the help of the Royal Air Force which introduced the first flying training syllabus and provided two ex-RAF pilots as instructors, as well as facilities and services at Seletar Airport. Finally, the first batch of six pilot trainees were sent to the United Kingdom in August 1968 to undergo training in various technical disciplines. The training was based on the Hawker Hunter, the SADC's first air defence fighter. The following month, another pioneer group of technicians, this time from the rotary wing, were sent to France to begin their technical training on the Aérospatiale Alouette III helicopter. In 1969, a number of local RAF technicians were released to join the fledgling SADC. These local


title: Republic of Singapore Air Force

text: technicians (local other ranks) had experience working on fixed-wing RAF aircraft such as the Hawker Hunter, Gloster Javelin, English Electric Canberra, English Electric Lightning and Avro Shackleton; as well as rotary-wing RAF aircraft such as the Bristol Belvedere, Westland Wessex and Westland Whirlwind.


title: Republic of Singapore Air Force

text: Eight Cessna 172K aircraft—the SADC's first—arrived in May 1969 to be used for basic pilot training. By December, the first batch of students completed the course. Of these, six were sent to the UK to receive further training. On their return to Singapore in 1970, they were ready to operate the then newly acquired Hawker Hunter fighter aircraft.


title: Republic of Singapore Air Force

text: The pace of training pilots and ground crew picked up gradually. On 1 August 1969, Minister for the Interior and Defence, Lim Kim San, inaugurated the Flying Training School (FTS) at Tengah Air Base (then known as RAF Tengah). The inauguration of FTS brought SADC closer to its goal of fulfilling the heavy responsibility of defending Singapore's airspace.


title: Republic of Singapore Air Force

text: The subsequent arrival of the BAC Strikemasters in 1969, used for advanced phase flying training, meant that pilot trainees were now able to earn their initial wings locally rather than overseas. The first batch of locally trained fighter pilots were trained at the FTS and graduated in November 1970. Amongst this batch was 2LT Goh Yong Siang, who later rose to the appointment of Chief of Air Force on 1 July 1995. Gradually, the SADC had its own pilots, flying instructors, air traffic controllers, and ground crew.


title: Republic of Singapore Air Force

text: When Britain brought forward its plan to withdraw its forces by September 1971, the SADC was suddenly entrusted with a huge responsibility and resources. Britain's former air bases—Tengah, Seletar, Sembawang and Changi—were handed over to the SADC, as well as its air defence radar station and Bloodhound II surface-to-air missiles.


title: Republic of Singapore Air Force

text: In 1973, the SADC procured Shorts Skyvan search-and-locate aircraft and Douglas A-4 Skyhawk fighter-bombers. With a reliable mix of fighters, fighter-bombers, helicopters and transport aircraft, the SADC was ready to assume the functions of a full-fledged air force. On 1 April 1975, the SADC was renamed the Republic of Singapore Air Force (RSAF).


title: Republic of Singapore Air Force

text: The RSAF celebrated its 50th Anniversary in 2018 with the theme "Our Home, Above All". The RSAF celebrated its Golden Jubilee with an extended flypast during the national day parade on 9 August and also performed 2 sessions of aerial display at the Marina Barrage on 11 and 12 August.


title: Republic of Singapore Air Force

text: On 5 January 2007, Defence minister Teo Chee Hean announced that the Air Force organisation chart will be re-structured into five major commands, namely the Air Defence and Operations Command (ADOC), the Air Combat Command (ACC), the Participation Command (PC), the Air Power Generation Command (APGC) and the Unmanned Aerial Vehicle (UAV) Command (UC). The first to be inaugurated was ADOC, along the restructuring announcement.


title: Republic of Singapore Air Force

text: ADOC is the principal agency in charge of planning and executing peacetime operations and air defence. ADOC is also responsible for the development and operational readiness of the command and control and ground-based air defence units of the RSAF.


title: Republic of Singapore Air Force

text: Unmanned Aerial Vehicle Command was the second command to be inaugurated and become operational in May 2007.


title: Republic of Singapore Air Force

text: The last two commands, ACC and APGC, were inaugurated together in August 2008 in conjunction with the RSAF 40th Anniversary. The ACC will bring together fighter and transport squadrons under one command, with central planning, control and execution of the air battle in operations. The APGC will enhance the missions of the ACC by ensuring that all air bases remain operational at all times, as well as improving the servicing and turn-around of aircraft to ensure continuous and responsive operations.


title: Republic of Singapore Air Force

text: The ACC ("Poised And Deadly") is responsible for the planning, control and execution of the air battle in operations. It brings together all fighter and transport squadrons that will carry out these tasks under a single command which will be responsible for training the pilots and aircrew to think and operate in a fully integrated way. The ACC consists of the following groups:


title: Republic of Singapore Air Force

text: The APGC ("Generate And Sustain") is set up to enable the RSAF to generate and sustain effective, timely and robust air power to meet the operational needs of the SAF. With the APGC, higher operational efficiency within each RSAF Air Base, and secondly, greater integration across the four bases are achieved. Units are classified under Air Base Operability (ABO) and Aircraft Generation (AcG). The APGC consists of the following groups:


title: Republic of Singapore Air Force

text: The four support squadrons still remain organic to each Base but are under direct command of APGC. These four squadrons are: Airfield Maintenance Squadron (AMS), Ground Logistics Squadron (GLS), Field Defence Squadron (FDS) and Flying Support Squadron (FSS).


title: Republic of Singapore Air Force

text: The main structures under UC("Persistent And Precise") are Operations & System Development Group (OSDG), headed by the Deputy Commander of UC. UC consists of the following groups:


title: Republic of Singapore Air Force

text: The Air Force Training Command (AFTC) is an amalgamation of the former Air Force School, Flying Training School and UAV Training school which facilitates training of future pilots and ground crew of the RSAF. It is located at 550 Airport Road, Singapore 534236.


title: Republic of Singapore Air Force

text: The backbone of the RSAF is formed by the Block 52/52+ F-16 Fighting Falcons. These are armed with US-supplied AIM-120C AMRAAM missiles and LANTIRN targeting pods, laser guided munitions and conformal fuel tanks for long-range strike.


title: Republic of Singapore Air Force

text: While Singapore initially bought as many as 70 F-16 planes, on 18 November 2004, it was announced that the RSAF would offer its remaining 7 F-16A/Bs to the Royal Thai Air Force. It is believed that these early Block 15OCU aircraft were upgraded to "Falcon One" standard by ST Aerospace before the transfer and delivered in late 2005. In return, the RSAF was permitted to train at the Udon Royal Thai Air Force Base in north-east Thailand for a specified number of days each year. This would mean that the RSAF will operate only the Block 52/52+ model, as many as 62 F-16CJ/DJ planes.


title: Republic of Singapore Air Force

text: Due to severe airspace constraints within Singapore, the RSAF operates its aircraft at several overseas locations to provide greater exposure to its pilots. With the F-16C/D Fighting Falcons, KC-135R Stratotankers, AH-64D Apaches and CH-47SD Chinook helicopters based in the United States, the Marchetti S-211s, PC-21s, and Super Puma helicopters in Australia, and the Alenia Aermacchi M-346 Master in France, almost one third of the force's inventory is based outside Singapore.


title: Republic of Singapore Air Force

text: In 1994, the RSAF commenced a modernisation program for its fleet of approximately 49 operational (R)F-5E and F-5F aircraft. The upgrade was performed by Singapore Technologies Aerospace (STAero) and the upgraded aircraft were designated (R)F-5S and F-5T respectively, operating from Paya Lebar Air Base. These upgraded F-5S/T, equipped with the Galileo Avionica's FIAR Grifo-F X-band Radar are thought to be capable of firing the AIM-120 AMRAAM missile but to date, no actual live-firing has actually been reported. For in-flight refuelling, four KC-135Rs and four KC-130Bs are commissioned to support the fighter force of F-16C/Ds and (R)F-5S/Ts.


title: Republic of Singapore Air Force

text: Airborne Early Warning and Control (AEW&C) capability was introduced in 1987 when four E-2C Hawkeyes were delivered to 111 Squadron. The duty of Maritime Patrol and Coastal surveillance is performed by the eight Fokker 50 MPA (entered service in 1991) of 121 Squadron, which can be armed with long-range anti-shipping AGM-84 Harpoon missiles and ASW torpedoes.


title: Republic of Singapore Air Force

text: As part of its fleet renewal process, the RSAF officially withdrew its fleet of ST Aerospace A-4SU Super Skyhawk from front-line service on 31 March 2005 after 31 years of operations. The A-4SUs' achievements included flying directly from Singapore to the Philippines, incorporating the RSAF's first air-to-air refuelling mission in 1986, as well as the excellent aerobatic display of the 'red and white' Super Skyhawks flown by the RSAF Black Knights during Asian Aerospace 1990. A month before its retirement, the Skyhawk squadron won top honours in a strike exercise against its more modern F-16 and F-5 counterparts.


title: Republic of Singapore Air Force

text: Singapore ordered a total of twenty AH-64D Apache Longbow attack helicopters in two batches. After a long period of negotiations over the delivery of the sophisticated Longbow Fire-control radar, the first batch of eight aircraft, fitted with the Fire Control Radar, was delivered on 17 May 2002. The second batch of 12 Apaches were ordered in 2001 even before the first delivery took place. All of the initial eight Apaches are based in the United States. Three of the Apache Longbows returned in January 2006 at the request of the Minister of Defence.


title: Republic of Singapore Air Force

text: Apart from the fifteen CH-47SDs delivered from 1996, a new batch of fifteen aircraft was ordered in 1997, with an option of four extra airframes. At least 30 CH-47SD have been delivered and are in service at Sembawang Air Base. It is believed that these had been upgraded to the SD standard prior to delivery.


title: Republic of Singapore Air Force

text: Eight CH-47SDs were also deployed to support the relief efforts in the aftermath of the 2004 Indian Ocean earthquake and tsunami. It was the first and one of the few countries to reach the affected areas. The RSAF deployed dozens of C-130Hs, CH-47SDs and AS 332Ms there along with three of the RSN's latest Landing Ship Tanks (RSS Endurance, RSS Persistence and RSS Endeavour of the "Endurance" class LST) as well as Singapore Armed Forces vehicles, engineers, and medical teams.


title: Republic of Singapore Air Force

text: In September 2005, the RSAF sent three CH-47SD Chinook helicopters, later augmented by a fourth CH-47SD Chinook, to provide assistance in the rescue and evacuation of stranded civilians after Hurricane Katrina struck New Orleans and nearby areas in the United States. The humanitarian effort by Singapore involved more aircraft than any other foreign countries.


title: Republic of Singapore Air Force

text: Since 2003, the RSAF has also made deployments of KC-135 tankers and C-130 aircraft to the Persian Gulf in support of the multinational efforts for the reconstruction of Iraq. RSAF personnel have carried out airlift, transportation and supply, and air-to-air refuelling missions in support of the multinational forces, assisting the Coalition in carrying supplies and personnel, transporting humanitarian material and conducting medical evacuation operations. In September 2013, Defence Minister Ng Eng Hen stated in a parliamentary reply that Singapore would soon acquire the Aster 30 land-based missile system.


title: Republic of Singapore Air Force

text: RSAF day is celebrated on 1 September annually, in 2018 a combined flypast including the new A330 MRTT with a special 50th anniversary livery took place at Tengah Air Base.


title: Republic of Singapore Air Force

text: Military ranks in the Singapore Armed Forces are identical across the three services except for the flag ranks of the RSN. They are based on the Army model. The official table of ranks stops at three stars for all three services. NATO rank codes are not officially used, but are listed here for easy comparison with other armed forces.


title: Republic of Singapore Air Force

text: Like the Navy, the majority of Air Force personnel are regulars. This is due to the specialised and technical nature of many jobs. The employment of National Servicemen in various roles are limited mostly to the infantry-like Field Defence Squadrons which do not require such specialised training.


title: Republic of Singapore Air Force

text: In February 2003, Singapore joined the JSF program's System Design and Development (SDD) Phase, as a Security Co-operation Participant (SCP). The first deliveries of the F-35 Lightning II are not expected before 2021, but replacement for the bulk of the A-4SUs was needed by 2007. As a start, 20 F-16D Block 52+ have been delivered from 2003 under project Peace Carvin IV.


title: Republic of Singapore Air Force

text: The RSAF embarked on its Next Generation Fighter (NGF) programme to replace the aging A-4SUs. The original list of competitors was shortlisted to the final two – Dassault Rafale and the Boeing F-15SG Strike Eagle. The F-15SG is a variant of the F-15E Strike Eagle and is similar in configuration to the F-15K sold to South Korea, but differs in the addition of the APG-63(V)3 active electronically scanned array (AESA) radar developed by Raytheon. The F-15SG is powered by two General Electric F110-GE-129 thrust engines. The DSTA (Defense Science & Technology Agency) conducted a detailed technical assessment, simulations, and other tests to assess the final selection. On 6 September 2005, it was announced that the F-15SG had won the contract over the Rafale. An initial order placed in 2005 for 12 aircraft with 8 options. On 22 October 2007, Singapore's Ministry of Defence (MINDEF) exercised the option to purchase eight more F-15SG fighters as part of the original contract signed in 2005. Along with this buy, an additional order for four F-15SGs was made, bringing the total number of F-15SGs purchased by the start of 2008 to 24.


title: Republic of Singapore Air Force

text: In January 2005, it was announced that 6 Sikorsky S-70B (derivative of SH-60 Seahawk) naval helicopters will be purchased, complete with anti-surface and anti-submarine weapons and sensors. 2 more Seahawks were ordered in 2013. The Seahawks are operated by RSAF pilots, with System Specialists of the Republic of Singapore Navy operating the sensors and weaponry. They operate from the Navy's new "Formidable" class frigates, and when operating from land are based at Sembawang Air Base. All 20 AH-64D Longbow attack helicopters have been delivered to the RSAF. 12 of these were deployed back to Singapore and took part in combined arms exercises with the Army, with the remaining 8 helicopters being part of the Peace Vanguard detachment based in the United States.


title: Republic of Singapore Air Force

text: In April 2007, it was announced that the 4 E-2C Hawkeyes were to be replaced with 4 Gulfstream G550s fitted with the IAI EL/W-2085 radar which would become the primary airborne early warning aircraft for the RSAF. Not included in the deal is an additional G550 as an AEW trainer, which will be acquired and maintained by ST Aerospace on behalf of RSAF.


title: Republic of Singapore Air Force

text: In July 2010, the Alenia Aermacchi M-346 Master was selected by the RSAF to replace the A-4SU in the Advanced Jet Training (AJT) role, currently based at BA 120 Cazaux Air Base in France. In a press release by the MINDEF on 28 September 2008, ST Aerospace had been awarded the contract to acquire twelve M-346 and a ground based training system on behalf of RSAF. As stipulated in the contract, ST Aerospace will act as the main contractor to maintain the aircraft after delivery by Alenia Aermacchi while Boeing would supply the training system. Delivery date is scheduled from 2012 onwards.


title: Republic of Singapore Air Force

text: The backbone of the transport fleet are the four KC-130B, one KC-130H and five C-130H Hercules transport aircraft, which are expected to remain in service through 2030, will be undergoing an extensive modernisation process to bring all ten existing airframes to the same common standard. The first airframe, a KC-130B, was returned to frontline service on 21 September 2010. ST Aerospace, the main contractor behind the project, is expected to upgrade the other nine airframes for the RSAF within the next seven years. Included in the package is the replacement of cockpit flight management system with a modern glass cockpit avionics suite, central engine displays to replace analogue gauges, improved voice communications, digital autopilot, flight director as well as a digital weather radar, which will make the aircraft Global Air Traffic Management-compliant. Also, the C-130Bs will receive an auxiliary power unit and environmental control system in common with the C-130Hs. Once the upgrade is completed, this will effectively give the RSAF five KC-130Hs and five C-130Hs.


title: Republic of Singapore Air Force

text: In December 2010, the RSAF issued a letter of request to inspect stored ex-US Navy P-3C Orion aircraft that have been retired from active duty. Lockheed Martin believes the RSAF has a requirement of 4 to 5 of these aircraft, which would be modernised extensively before reintroduction into active service.


title: Republic of Singapore Air Force

text: On 30 June 2018, Defence Minister Ng Eng Hen announced that the F-16's replacement will be announced soon. Meanwhile, the KC-135Rs are being replaced by the A330 MRTT while replacements for other fixed-wing aircraft and helicopters are announced.


title: Republic of Singapore Air Force

text: On 18 January 2019, MINDEF officially confirmed the procurement of F-35s for a full evaluation of their capabilities and suitability before deciding on a full fleet to replace the aging F-16 fleet. On 1 March 2019, MINDEF announced that they will send a Letter of Request (LOR) to purchase 4 F-35s with an option of 8 more after the evaluation. On 9 January 2020 the U.S. Defense Security Cooperation Agency approved a possible sale to Singapore of four F-35B short takeoff and vertical landing (STOVL) variants with the option to purchase an additional eight F-35Bs and up to 13 Pratt & Whitney F135 engines and other related equipment for an estimated total cost of $2.75 billion.


title: Republic of Singapore Air Force

text: First formed in 1973 at Tengah Air Base, the Black Knights is RSAF's official aerobatic team and has been performing on an ad hoc basis since its inception, with volunteer pilots drawn from various front line squadrons within the RSAF. The aerobatics team has performed on events including the Singapore Airshow 2014.


title: Republic of Singapore Air Force

text: The RSAF maintains the Air Force Museum, which was first located at Changi Air Base before it was relocated to a purpose-built building currently situated at 400 Airport Road, Singapore 534234 adjacent to Paya Lebar Air Base. The museum is open to the public and showcases the air force's history and capabilities. Exhibits include the Northrop Grumman E-2 Hawkeye and numerous A-4SU Super Skyhawk.


title: Republic of Singapore Air Force

text: The Republic of Singapore Air Force has loaned several aircraft, and aircraft parts to the tertiary institutions in Singapore, including Institute of Technical Education, Ngee Ann Polytechnic, Singapore Polytechnic, Nanyang Polytechnic and Nanyang Technological University since 2005. Aircraft includes the A-4SU Super Skyhawk.


title: Fluorescent lamp

text: A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet light that then causes a phosphor coating on the inside of the lamp to glow. A fluorescent lamp converts electrical energy into useful light much more efficiently than an incandescent lamp. The typical luminous efficacy of fluorescent lighting systems is 50–100 lumens per watt, several times the efficacy of incandescent bulbs with comparable light output. For comparison, the luminous efficacy of an incandescent bulb may only be 16 lumens per watt.


title: Fluorescent lamp

text: Fluorescent lamp fixtures are more costly than incandescent lamps because, among other things, they require a ballast to regulate current through the lamp, but the initial cost is offset by a much lower running cost. Compact fluorescent lamps are now available in the same popular sizes as incandescents and are used as an energy-saving alternative in homes.


title: Fluorescent lamp

text: Because they contain mercury, many fluorescent lamps are classified as hazardous waste. The United States Environmental Protection Agency recommends that fluorescent lamps be segregated from general waste for recycling or safe disposal, and some jurisdictions require recycling of them.


title: Fluorescent lamp

text: The fluorescence of certain rocks and other substances had been observed for hundreds of years before its nature was understood. By the middle of the 19th century, experimenters had observed a radiant glow emanating from partially evacuated glass vessels through which an electric current passed. One of the first to explain it was the Irish scientist Sir George Stokes from the University of Cambridge in 1852, who named the phenomenon "fluorescence" after fluorite, a mineral many of whose samples glow strongly because of impurities. The explanation relied on the nature of electricity and light phenomena as developed by the British scientists Michael Faraday in the 1840s and James Clerk Maxwell in the 1860s.


title: Fluorescent lamp

text: Little more was done with this phenomenon until 1856 when German glassblower Heinrich Geissler created a mercury vacuum pump that evacuated a glass tube to an extent not previously possible. Geissler invented the first gas-discharge lamp, the Geissler tube, consisting of a partially evacuated glass tube with a metal electrode at either end. When a high voltage was applied between the electrodes, the inside of the tube lit up with a glow discharge. By putting different chemicals inside, the tubes could be made to produce a variety of colors, and elaborate Geissler tubes were sold for entertainment. More important, however, was its contribution to scientific research. One of the first scientists to experiment with a Geissler tube was Julius Plücker, who systematically described in 1858 the luminescent effects that occurred in a Geissler tube. He also made the important observation that the glow in the tube shifted position when in proximity to an electromagnetic field. Alexandre Edmond Becquerel observed in 1859 that certain substances gave off light when they were placed in a Geissler tube. He went on to apply thin coatings of luminescent materials to the surfaces of these tubes. Fluorescence occurred, but the tubes were very inefficient and had a short operating life.


title: Fluorescent lamp

text: Inquiries that began with the Geissler tube continued as even better vacuums were produced. The most famous was the evacuated tube used for scientific research by William Crookes. That tube was evacuated by the highly effective mercury vacuum pump created by Hermann Sprengel. Research conducted by Crookes and others ultimately led to the discovery of the electron in 1897 by J. J. Thomson and X-rays in 1895 by Wilhelm Röntgen. But the Crookes tube, as it came to be known, produced little light because the vacuum in it was too good and thus lacked the trace amounts of gas that are needed for electrically stimulated luminescence.


title: Fluorescent lamp

text: Thomas Edison briefly pursued fluorescent lighting for its commercial potential. He invented a fluorescent lamp in 1896 that used a coating of calcium tungstate as the fluorescing substance, excited by X-rays, but although it received a patent in 1907, it was not put into production. As with a few other attempts to use Geissler tubes for illumination, it had a short operating life, and given the success of the incandescent light, Edison had little reason to pursue an alternative means of electrical illumination. Nikola Tesla made similar experiments in the 1890s, devising high-frequency powered fluorescent bulbs that gave a bright greenish light, but as with Edison's devices, no commercial success was achieved.


title: Fluorescent lamp

text: One of Edison's former employees created a gas-discharge lamp that achieved a measure of commercial success. In 1895 Daniel McFarlan Moore demonstrated lamps in length that used carbon dioxide or nitrogen to emit white or pink light, respectively. They were considerably more complicated than an incandescent bulb, requiring both a high-voltage power supply and a pressure-regulating system for the fill gas.


title: Fluorescent lamp

text: Moore invented an electromagnetically controlled valve that maintained a constant gas pressure within the tube, to extend the working life. Although Moore's lamp was complicated, expensive, and required very high voltages, it was considerably more efficient than incandescent lamps, and it produced a closer approximation to natural daylight than contemporary incandescent lamps. From 1904 onwards Moore's lighting system was installed in a number of stores and offices. Its success contributed to General Electric’s motivation to improve the incandescent lamp, especially its filament. GE's efforts came to fruition with the invention of a tungsten-based filament. The extended lifespan and improved efficacy of incandescent bulbs negated one of the key advantages of Moore's lamp, but GE purchased the relevant patents in 1912. These patents and the inventive efforts that supported them were to be of considerable value when the firm took up fluorescent lighting more than two decades later.


title: Fluorescent lamp

text: At about the same time that Moore was developing his lighting system, Peter Cooper Hewitt invented the mercury-vapor lamp, patented in 1901 (). Hewitt's lamp glowed when an electric current was passed through mercury vapor at a low pressure. Unlike Moore's lamps, Hewitt's were manufactured in standardized sizes and operated at low voltages. The mercury-vapor lamp was superior to the incandescent lamps of the time in terms of energy efficiency, but the blue-green light it produced limited its applications. It was, however, used for photography and some industrial processes.


title: Fluorescent lamp

text: Mercury vapor lamps continued to be developed at a slow pace, especially in Europe, and by the early 1930s, they received limited use for large-scale illumination. Some of them employed fluorescent coatings, but these were used primarily for color correction and not for enhanced light output. Mercury vapor lamps also anticipated the fluorescent lamp in their incorporation of a ballast to maintain a constant current.


title: Fluorescent lamp

text: Cooper-Hewitt had not been the first to use mercury vapor for illumination, as earlier efforts had been mounted by Way, Rapieff, Arons, and Bastian and Salisbury. Of particular importance was the mercury-vapor lamp invented by Küch and Retschinsky in Germany. The lamp used a smaller bore bulb and higher current operating at higher pressures. As a consequence of the current, the bulb operated at a higher temperature which necessitated the use of a quartz bulb. Although its light output relative to electrical consumption was better than that of other sources of light, the light it produced was similar to that of the Cooper-Hewitt lamp in that it lacked the red portion of the spectrum, making it unsuitable for ordinary lighting. Due to difficulties in sealing the electrodes to the quartz, the lamp had a very short life.


title: Fluorescent lamp

text: The next step in gas-based lighting took advantage of the luminescent qualities of neon, an inert gas that had been discovered in 1898 by isolation from the atmosphere. Neon glowed a brilliant red when used in Geissler tubes. By 1910, Georges Claude, a Frenchman who had developed a technology and a successful business for air liquefaction, was obtaining enough neon as a byproduct to support a neon lighting industry. While neon lighting was used around 1930 in France for general illumination, it was no more energy-efficient than conventional incandescent lighting. Neon tube lighting, which also includes the use of argon and mercury vapor as alternative gases, came to be used primarily for eye-catching signs and advertisements. Neon lighting was relevant to the development of fluorescent lighting, however, as Claude's improved electrode (patented in 1915) overcame "sputtering", a major source of electrode degradation. Sputtering occurred when ionized particles struck an electrode and tore off bits of metal. Although Claude's invention required electrodes with a lot of surface area, it showed that a major impediment to gas-based lighting could be overcome.


title: Fluorescent lamp

text: The development of the neon light also was significant for the last key element of the fluorescent lamp, its fluorescent coating. In 1926 Jacques Risler received a French patent for the application of fluorescent coatings to neon light tubes. The main use of these lamps, which can be considered the first commercially successful fluorescents, was for advertising, not general illumination. This, however, was not the first use of fluorescent coatings; Becquerel had earlier used the idea and Edison used calcium tungstate for his unsuccessful lamp. Other efforts had been mounted, but all were plagued by low efficiency and various technical problems. Of particular importance was the invention in 1927 of a low-voltage “metal vapor lamp” by Friedrich Meyer, Hans-Joachim Spanner, and Edmund Germer, who were employees of a German firm in Berlin. A German patent was granted but the lamp never went into commercial production.


title: Fluorescent lamp

text: All the major features of fluorescent lighting were in place at the end of the 1920s. Decades of invention and development had provided the key components of fluorescent lamps: economically manufactured glass tubing, inert gases for filling the tubes, electrical ballasts, long-lasting electrodes, mercury vapor as a source of luminescence, effective means of producing a reliable electrical discharge, and fluorescent coatings that could be energized by ultraviolet light. At this point, intensive development was more important than basic research.


title: Fluorescent lamp

text: In 1934, Arthur Compton, a renowned physicist and GE consultant, reported to the GE lamp department on successful experiments with fluorescent lighting at General Electric Co., Ltd. in Great Britain (unrelated to General Electric in the United States). Stimulated by this report, and with all of the key elements available, a team led by George E. Inman built a prototype fluorescent lamp in 1934 at General Electric’s Nela Park (Ohio) engineering laboratory. This was not a trivial exercise; as noted by Arthur A. Bright, "A great deal of experimentation had to be done on lamp sizes and shapes, cathode construction, gas pressures of both argon and mercury vapor, colors of fluorescent powders, methods of attaching them to the inside of the tube, and other details of the lamp and its auxiliaries before the new device was ready for the public."


title: Fluorescent lamp

text: In addition to having engineers and technicians along with facilities for R&D work on fluorescent lamps, General Electric controlled what it regarded as the key patents covering fluorescent lighting, including the patents originally issued to Hewitt, Moore, and Küch. More important than these was a patent covering an electrode that did not disintegrate at the gas pressures that ultimately were employed in fluorescent lamps. Albert W. Hull of GE's Schenectady Research Laboratory filed for a patent on this invention in 1927, which was issued in 1931. General Electric used its control of the patents to prevent competition with its incandescent lights and probably delayed the introduction of fluorescent lighting by 20 years. Eventually, war production required 24-hour factories with economical lighting, and fluorescent lights became available.


title: Fluorescent lamp

text: While the Hull patent gave GE a basis for claiming legal rights over the fluorescent lamp, a few months after the lamp went into production the firm learned of a U.S. patent application that had been filed in 1927 for the aforementioned "metal vapor lamp" invented in Germany by Meyer, Spanner, and Germer. The patent application indicated that the lamp had been created as a superior means of producing ultraviolet light, but the application also contained a few statements referring to fluorescent illumination. Efforts to obtain a U.S. patent had met with numerous delays, but were it to be granted, the patent might have caused serious difficulties for GE. At first, GE sought to block the issuance of a patent by claiming that priority should go to one of their employees, Leroy J. Buttolph, who according to their claim had invented a fluorescent lamp in 1919 and whose patent application was still pending. GE also had filed a patent application in 1936 in Inman's name to cover the “improvements” wrought by his group. In 1939 GE decided that the claim of Meyer, Spanner, and Germer had some merit, and that in any event a long interference procedure was not in their best interest. They therefore dropped the Buttolph claim and paid $180,000 to acquire the Meyer, et al. application, which at that point was owned by a firm known as Electrons, Inc. The patent was duly awarded in December 1939. This patent, along with the Hull patent, put GE on what seemed to be firm legal ground, although it faced years of legal challenges from Sylvania Electric Products, Inc., which claimed infringement on patents that it held.


title: Fluorescent lamp

text: Even though the patent issue was not completely resolved for many years, General Electric's strength in manufacturing and marketing gave it a pre-eminent position in the emerging fluorescent light market. Sales of "fluorescent lumiline lamps" commenced in 1938 when four different sizes of tubes were put on the market. They were used in fixtures manufactured by three leading corporations, Lightolier, Artcraft Fluorescent Lighting Corporation, and Globe Lighting. The Slimline fluorescent ballast's public


title: Fluorescent lamp

text: introduction in 1946 was by Westinghouse and General Electric and Showcase/Display Case fixtures were introduced by Articraft Fluorescent Lighting Corporation in 1946. During the following year, GE and Westinghouse publicized the new lights through exhibitions at the New York World's Fair and the Golden Gate International Exposition in San Francisco. Fluorescent lighting systems spread rapidly during World War II as wartime manufacturing intensified lighting demand. By 1951 more light was produced in the United States by fluorescent lamps than by incandescent lamps.


title: Fluorescent lamp

text: In the first years zinc orthosilicate with varying content of beryllium was used as greenish phosphor. Small additions of magnesium tungstate improved the blue part of the spectrum yielding acceptable white. After it was discovered that beryllium was toxic, halophosphate-based phosphors took over.


title: Fluorescent lamp

text: The fundamental mechanism for the conversion of electrical energy to light is the emission of a photon when an electron in a mercury atom falls from an excited state into a lower energy level. Electrons flowing in the arc collide with the mercury atoms. If the incident electron has enough kinetic energy, it transfers energy to the atom's outer electron, causing that electron to temporarily jump up to a higher energy level that is not stable. The atom will emit an ultraviolet photon as the atom's electron reverts to a lower, more stable, energy level. Most of the photons that are released from the mercury atoms have wavelengths in the ultraviolet (UV) region of the spectrum, predominantly at wavelengths of 253.7 and 185 nanometers (nm). These are not visible to the human eye, so ultraviolet energy is converted to visible light by the fluorescence of the inner phosphor coating. The difference in energy between the absorbed ultra-violet photon and the emitted visible light photon goes toward heating up the phosphor coating.


title: Fluorescent lamp

text: Electric current flows through the tube in a low-pressure arc discharge. Electrons collide with and ionize noble gas atoms inside the bulb surrounding the filament to form a plasma by the process of impact ionization. As a result of avalanche ionization, the conductivity of the ionized gas rapidly rises, allowing higher currents to flow through the lamp.


title: Fluorescent lamp

text: The fill gas helps determine the electrical characteristics of the lamp but does not give off light itself. The fill gas effectively increases the distance that electrons travel through the tube, which allows an electron a greater chance of interacting with a mercury atom. Additionally, argon atoms, excited to a metastable state by the impact of an electron, can impart energy to a mercury atom and ionize it, described as the Penning effect. This lowers the breakdown and operating voltage of the lamp, compared to other possible fill gases such as krypton.


title: Fluorescent lamp

text: A fluorescent lamp tube is filled with a mix of argon, xenon, neon, or krypton, and mercury vapor. The pressure inside the lamp is around 0.3% of atmospheric pressure. The partial pressure of the mercury vapor alone is about 0.8 Pa (8 millionths of atmospheric pressure), in a T12 40-watt lamp. The inner surface of the lamp is coated with a fluorescent coating made of varying blends of metallic and rare-earth phosphor salts. The lamp's electrodes are typically made of coiled tungsten and are coated with a mixture of barium, strontium and calcium oxides to improve thermionic emission.


title: Fluorescent lamp

text: Fluorescent lamp tubes are often straight and range in length from about for miniature lamps, to for high-output lamps. Some lamps have the tube bent into a circle, used for table lamps or other places where a more compact light source is desired. Larger U-shaped lamps are used to provide the same amount of light in a more compact area, and are used for special architectural purposes. Compact fluorescent lamps have several small-diameter tubes joined in a bundle of two, four, or six, or a small diameter tube coiled into a helix, to provide a high amount of light output in little volume.


title: Fluorescent lamp

text: Light-emitting phosphors are applied as a paint-like coating to the inside of the tube. The organic solvents are allowed to evaporate, then the tube is heated to nearly the melting point of glass to drive off remaining organic compounds and fuse the coating to the lamp tube. Careful control of the grain size of the suspended phosphors is necessary; large grains lead to weak coatings, and small particles leads to poor light maintenance and efficiency. Most phosphors perform best with a particle size around 10 micrometers. The coating must be thick enough to capture all the ultraviolet light produced by the mercury arc, but not so thick that the phosphor coating absorbs too much visible light. The first phosphors were synthetic versions of naturally occurring fluorescent minerals, with small amounts of metals added as activators. Later other compounds were discovered, allowing differing colors of lamps to be made.


title: Fluorescent lamp

text: Fluorescent lamps are negative differential resistance devices, so as more current flows through them, the electrical resistance of the fluorescent lamp drops, allowing for even more current to flow. Connected directly to a constant-voltage power supply, a fluorescent lamp would rapidly self-destruct because of the uncontrolled current flow. To prevent this, fluorescent lamps must use a ballast to regulate the current flow through the lamp.


title: Fluorescent lamp

text: The terminal voltage across an operating lamp varies depending on the arc current, tube diameter, temperature, and fill gas. A general lighting service T12 lamp operates at 430 mA, with 100 volts drop. High-output lamps operate at 800 mA, and some types operate up to 1.5 A. The power level varies from 33 to 82 watts per meter of tube length (10 to 25 W/ft) for T12 lamps.


title: Fluorescent lamp

text: The simplest ballast for alternating current (AC) use is an inductor placed in series, consisting of a winding on a laminated magnetic core. The inductance of this winding limits the flow of AC current. This type of ballast are common in 220–240V countries (And in North America, up to 30W lamps). Ballasts are rated for the size of lamp and power frequency. In North America, the AC voltage is insufficient to start long fluorescent lamps, so the ballast is often a step-up autotransformer with substantial leakage inductance (so as to limit the current flow). Either form of inductive ballast may also include a capacitor for power factor correction.


title: Fluorescent lamp

text: Fluorescent lamps can run directly from a direct current (DC) supply of sufficient voltage to strike an arc. The ballast must be resistive, and would consume about as much power as the lamp. When operated from DC, the starting switch is often arranged to reverse the polarity of the supply to the lamp each time it is started; otherwise, the mercury accumulates at one end of the tube. Fluorescent lamps are (almost) never operated directly from DC for those reasons. Instead, an inverter converts the DC into AC and provides the current-limiting function as described below for electronic ballasts.


title: Fluorescent lamp

text: The performance of fluorescent lamps is critically affected by the temperature of the bulb wall and its effect on the partial pressure of mercury vapor within the lamp. Since mercury condenses at the coolest spot in the lamp, careful design is required to maintain that spot at the optimum temperature, around .


title: Fluorescent lamp

text: Using an amalgam with some other metal reduces the vapor pressure and extends the optimum temperature range upward; however, the bulb wall "cold spot" temperature must still be controlled to prevent condensing. High-output fluorescent lamps have features such as a deformed tube or internal heat-sinks to control cold spot temperature and mercury distribution. Heavily loaded small lamps, such as compact fluorescent lamps, also include heat-sink areas in the tube to maintain mercury vapor pressure at the optimum value.


title: Fluorescent lamp

text: Only a fraction of the electrical energy input into a lamp is converted to useful light. The ballast dissipates some heat; electronic ballasts may be around 90% efficient. A fixed voltage drop occurs at the electrodes, which also produces heat. Some of the energy in the mercury vapor column is also dissipated, but about 85% is turned into visible and ultraviolet light.


title: Fluorescent lamp

text: Not all the UV radiation striking the phosphor coating is converted to visible light; some energy is lost. The largest single loss in modern lamps is due to the lower energy of each photon of visible light, compared to the energy of the UV photons that generated them (a phenomenon called Stokes shift). Incident photons have an energy of 5.5 electron volts but produce visible light photons with energy around 2.5 electron volts, so only 45% of the UV energy is used; the rest is dissipated as heat.


title: Fluorescent lamp

text: Most fluorescent lamps use electrodes that emit electrons into the tube by heat, known as hot cathodes. However, cold cathode tubes have cathodes that emit electrons only due to the large voltage between the electrodes. The cathodes will be warmed by current flowing through them, but are not hot enough for significant thermionic emission. Because cold cathode lamps have no thermionic emission coating to wear out, they can have much longer lives than hot cathode tubes. This makes them desirable for long-life applications (such as backlights in liquid crystal displays). Sputtering of the electrode may still occur, but electrodes can be shaped (e.g. into an internal cylinder) to capture most of the sputtered material so it is not lost from the electrode.


title: Fluorescent lamp

text: Cold cathode lamps are generally less efficient than thermionic emission lamps because the cathode fall voltage is much higher. Power dissipated due to cathode fall voltage does not contribute to light output. However, this is less significant with longer tubes. The increased power dissipation at tube ends also usually means cold cathode tubes have to be run at a lower loading than their thermionic emission equivalents. Given the higher tube voltage required anyway, these tubes can easily be made long, and even run as series strings. They are better suited for bending into special shapes for lettering and signage, and can also be instantly switched on or off.


title: Fluorescent lamp

text: The gas used in the fluorescent tube must be ionized before the arc can "strike" . For small lamps, it does not take much voltage to strike the arc and starting the lamp presents no problem, but larger tubes require a substantial voltage (in the range of a thousand volts). Many different starting circuits have been used. The choice of circuit is based on cost, AC voltage, tube length, instant versus non-instant starting, temperature ranges and parts availability.


title: Fluorescent lamp

text: Preheating, also called switchstart, uses a combination filament–cathode at each end of the lamp in conjunction with a mechanical or automatic (bi-metallic) switch (see circuit diagram to the right) that initially connect the filaments in series with the ballast to preheat them; after a short preheating time the starting switch opens. If timed correctly relatively to the mains supply, this causes the ballast to induce a voltage over the tube high enough to initiate the starting arc. These systems are standard equipment in 200–240 V countries (and for 100–120 V lamps up to about 30 watts).


title: Fluorescent lamp

text: Before the 1960s, four-pin thermal starters and manual switches were used. A glow switch starter automatically preheats the lamp cathodes. It consists of a normally open bi-metallic switch in a small sealed gas-discharge lamp containing inert gas (neon or argon). The glow switch will cyclically warm the filaments and initiate a pulse voltage to strike the arc; the process repeats until the lamp is lit. Once the tube strikes, the impinging main discharge keeps the cathodes hot, permitting continued electron emission. The starter switch does not close again because the voltage across the lit tube is insufficient to start a glow discharge in the starter.


title: Fluorescent lamp

text: With glow switch starters a failing tube will cycle repeatedly. Some starter systems used a thermal over-current trip to detect repeated starting attempts and disable the circuit until manually reset.


title: Fluorescent lamp

text: A power factor correction (PFC) capacitor draws leading current from the mains to compensate for the lagging current drawn by the lamp circuit.


title: Fluorescent lamp

text: Electronic starters use a different method to preheat the cathodes. They may be plug-in interchangeable with glow starters. They use a semiconductor switch and "soft start" the lamp by preheating the cathodes before applying a starting pulse which strikes the lamp first time without flickering; this dislodges a minimal amount of material from the cathodes during starting, giving longer lamp life. This is claimed to prolong lamp life by a factor of typically 3 to 4 times for a lamp frequently switched on as in domestic use, and to reduce the blackening of the ends of the lamp typical of fluorescent tubes. The circuit is typically complex, but the complexity is built into the IC. Electronic starters may be optimized for fast starting (typical start time of 0.3 seconds), or for most reliable starting even at low temperatures and with low supply voltages, with a startup time of 2–4 seconds. The faster-start units may produce audible noise during start-up.


title: Fluorescent lamp

text: Electronic starters only attempt to start a lamp for a short time when power is initially applied, and do not repeatedly attempt to restrike a lamp that is dead and unable to sustain an arc; some automatically stop trying to start a failed lamp. This eliminates the re-striking of a lamp and the continuous flashing of a failing lamp with a glow starter. Electronic starters are not subject to wear and do not need replacing periodically, although they may fail like any other electronic circuit. Manufacturers typically quote lives of 20 years, or as long as the light fitting.


title: Fluorescent lamp

text: "Instant start" fluorescent tubes were invented in 1944. Instant start simply uses a high enough voltage to break down the gas column and thereby start arc conduction. Once the high-voltage spark "strikes" the arc, the current is boosted until a glow discharge forms. As the lamp warms and pressure increases, the current continues to rise and both resistance and voltage falls, until mains or line-voltage takes over and the discharge becomes an arc. These tubes have no filaments and can be identified by a single pin at each end of the tube (for common lamps; compact cold-cathode lamps may also have a single pin, but operate from a transformer rather than a ballast). The lamp holders have a "disconnect" socket at the low-voltage end which disconnects the ballast when the tube is removed, to prevent electric shock. Instant-start lamps are slightly more energy efficient than rapid start, because they do not constantly send a heating current to the cathodes during operation, but the cold cathodes starting increases sputter, and they take much longer to transition from a glow discharge to an arc during warm up, thus the lifespan is typically about half of those seen in comparable rapid-start lamps.


title: Fluorescent lamp

text: Because the formation of an arc requires the thermionic emission of large quantities of electrons from the cathode, "rapid start" ballast designs provide windings within the ballast that continuously warm the cathode filaments. Usually operating at a lower arc voltage than the instant start design; no inductive voltage spike is produced for starting, so the lamps must be mounted near a grounded (earthed) reflector to allow the glow discharge to propagate through the tube and initiate the arc discharge via capacitive coupling. In some lamps a grounded "starting aid" strip is attached to the outside of the lamp glass. This ballast type is incompatible with the European energy saver T8 fluorescent lamps because these lamps requires a higher starting voltage than that of the open circuit voltage of rapid start ballasts.


title: Fluorescent lamp

text: Quick-start ballasts use a small auto-transformer to heat the filaments when power is first applied. When an arc strikes, the filament heating power is reduced and the tube will start within half a second. The auto-transformer is either combined with the ballast or may be a separate unit. Tubes need to be mounted near an earthed metal reflector in order for them to strike. Quick-start ballasts are more common in commercial installations because of lower maintenance costs. A quick-start ballast eliminates the need for a starter switch, a common source of lamp failures. Nonetheless, Quick-start ballasts are also used in domestic (residential) installations because of the desirable feature that a Quick-start ballast light turns on nearly immediately after power is applied (when a switch is turned on). Quick-start ballasts are used only on 240 V circuits and are designed for use with the older, less efficient T12 tubes.


title: Fluorescent lamp

text: The semi-resonant start circuit was invented by Thorn Lighting for use with T12 fluorescent tubes. This method uses a double wound transformer and a capacitor. With no arc current, the transformer and capacitor resonate at line frequency and generate about twice the supply voltage across the tube, and a small electrode heating current. This tube voltage is too low to strike the arc with cold electrodes, but as the electrodes heat up to thermionic emission temperature, the tube striking voltage falls below that of the ringing voltage, and the arc strikes. As the electrodes heat, the lamp slowly, over three to five seconds, reaches full brightness. As the arc current increases and tube voltage drops, the circuit provides current limiting.