Ultraviolet radiation is invisible to the human eye, but illuminating certain materials with UV radiation causes the emission of visible light, causing these substances to glow with various colors. This is called fluorescence, and has many practical uses.<unk> s are required to observe fluorescence, since other types of ultraviolet lamps emit visible light which drowns out the dim fluorescent glow.<unk>  is commonly used to authenticate oil paintings, antiques and banknotes.<unk> s can be used to differentiate real currency from counterfeit notes because, in many countries, legal banknotes have fluorescent symbols on them that only show under a<unk> . In addition, the paper used for printing money does not contain any of the brightening agents which cause commercially available papers to fluoresce under<unk> . Both of these features make illegal notes easier to detect and more difficult to successfully counterfeit. The same security features can be applied to identification cards such as passports or driver's licenses. Other security applications include the use of pens containing a fluorescent ink, generally with a soft tip, that can be used to "invisibly" mark items. If the objects that are so marked are subsequently stolen, a<unk>  can be used to search for these security markings. At some amusement parks, nightclubs and at other, day-long (or night-long) events, a fluorescent mark is rubber stamped onto the wrist of a guest who can then exercise the option of leaving and being able to return again without paying another admission fee. In medicine, the Wood's lamp is used to check for the characteristic fluorescence of certain dermatophytic fungi such as species of Microsporum which emit a yellow glow, or Corynebacterium which have a red to orange color when viewed under a Wood's lamp. Such light is also used to detect the presence and extent of disorders that cause a loss of pigmentation, such as vitiligo. It can also be used to diagnose other fungal infections such as ringworm, Microsporum canis, tinea versicolor; bacterial infections such erythrasma; other skin conditions including acne, scabies, alopecia, porphyria; as well as corneal scratches, foreign bodies in the eye, and<unk> ocked tear ducts. Fluorescent materials are also very widely used in numerous applications in molecular biology, often as "tags" which bind themselves to a substance of interest (for example, DNA), so allowing their visualization.<unk>  can also be used to see animal excreta such as urine and vomit that is not always visible to the naked eye.<unk>  is used extensively in non-destructive testing. Fluorescing fluids are applied to metal structures and illuminated with a<unk>  which allows cracks and other weaknesses in the material to be easily detected. It is also used to illuminate pictures painted with fluorescent colors, particularly on<unk> ack velvet, which intensifies the illusion of self-illumination. The use of such materials, often in the form of tiles viewed in a sensory room under UV light, is common in the United Kingdom for the education of students with profound and multiple learning difficulties. Such fluorescence from certain textile fibers, especially those bearing optical brightener residues, can also be used for recreational effect, as seen, for example, in the opening credits of the James Bond film A View to a Kill.<unk>  puppetry is also performed in a<unk>  theater. One of the innovations for night and all-weather flying used by the US, UK, Japan and Germany during World War II was the use of UV interior lighting to illuminate the instrument panel, giving a safer alternative to the radium-painted instrument faces and pointers, and an intensity that could be varied easily and without visible illumination that would give away an aircraft's position. This went so far as to include the printing of charts that were marked in UV-fluorescent inks, and the provision of UV-visible pencils and slide rules such as the E6B. Thousands of moth and insect collectors all over the world use various types of<unk> s to attract moth and insect specimens for photography and collecting. It is one of the preferred light sources for attracting insects and moths at night. It may also be used to test for LSD, which fluoresces under<unk>  while common substitutes such as 25I-NBOMe do not. In addition, if a leak is suspected in a refrigerator or an air conditioning system, a UV tracer dye can be injected into the system along with the compressor lubricant oil and refrigerant mixture. The system is then run in order to circulate the dye across the piping and components and then the system is examined with a<unk>  lamp. Any evidence of fluorescent dye then pinpoints the leaking part which needs replacement. File:US $20 under<unk> .The security thread of a US $20 bill glows green under<unk>  as a safeguard against counterfeiting. File:PRC E-Passport Info Page under<unk> .Anti-counterfeiting design of a Chinese passport glows under<unk> . File:Sorpion Under<unk> .Scorpion fluorescing under ultraviolet from a<unk>  File:Ultraschall Club Munich 2001 16.Decorative use of<unk>  in a nightclub
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