it is understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims . in embodiments of the present invention , the led luminaire employs a fin structure with hollow fins to dissipate heat to the environment . the hollow space inside the fins is connected to a chamber , where a liquid to vapor phase change material ( l - v pcm ) is provided to transfer heat from the led chips to the surfaces of the fins . in some embodiments , led chips are mounted on different evaporators , including chip - area evaporators and mounting and thermal block evaporators . chip - area evaporators use the back surface of chips mosaicked in a mounting block as the evaporator surface . mounting and thermal block evaporators are made of a copper sheet with a thickness of about 1 - 5 mm and the led chips are mounted on the copper sheet . the copper sheet spread the heat from a chip area ( about 1 mm 2 ) to a relatively larger area ( about 1 to 2 cm 2 ). both of these two kinds of evaporator surface are treated to be a hydrophilic surface . the evaporator with led chips is packaged in a 3 - d vacuum - sealed enclosure which forms a chamber . the sealed chamber can have a high vacuum , medium vacuum , or low vacuum . in all embodiments , a liquid to vapor phase change materials ( l - v pcms ) with a desired boiling temperatures ( e . g ., room temperature to 100 ° c .) is used to wet the evaporator surfaces during led luminaire operation . the l - v pcm may be stored in a reservoir integrated with the 3 - d enclosure . additional wick structure or fiber materials can also be implemented to use capillary force effect to transport the l - v pcm from the reservoir to the evaporator surface . the hydrophilic surface of the evaporator spreads l - v pcm uniformly to keep the surface wet . during the high power led chip operation , as the evaporator surface temperature rises , which can exceed the boiling temperature of the liquid , the l - v pcm liquid layer evaporates and carries away the heat from the evaporator surfaces . the heat carried by the vapor is transferred to the cold surfaces of the 3 - d enclosure and the vapor condensed back into the liquid . the liquid then is transferred back to the l - v pcm reservoir or the evaporator surface by gravitational force or other methods to continue the cycle . in some embodiments , the cold surfaces are the surfaces of containers which contain a solid to liquid pcm ( s - l pcm ) with a melting temperature slightly lower than the desired maximum operating temperature of the led chips . the s - l pcm containers are packaged in the chamber or another 3 - d enclosure with their surfaces spaced away from each other with small gaps . the surfaces of the s - l pcm container can be coated with a hydrophobic thin film to increase heat exchange coefficient of vapor to liquid phase change . the s - l pcm containers can have a geometry of flat plate or cylindrical shape , preferably with a thin thickness or small diameter . in this way , the evaporator surface and the s - l pcm container surfaces are thermally “ short circuited ” with negligible temperature difference . the heat on the evaporator surface is then transferred on the surface of the s - l pcm containers and thermally stored in the s - l pcm materials as the s - l pcm materials melt into a liquid . after the led luminaire is turned off , the heat stored in s - l pcm is dissipated into the environment by natural air convection . an led light according to a first embodiment of the present invention is illustrated in fig4 ( schematic cross - sectional view ). a hollow fin structure 405 is used to dissipate heat to the environment . the exterior shapes of the fins are flat plates arranged substantially parallel to each other , but each fin is hollow inside , and the hollow space of each fin is in fluid / vapor communication with an interior space ( chamber ) 410 of the led light . the fin structure 405 , also referred to as a 3 - d enclosure , may be formed of thin metal sheets that enclose the hollow space . the hollow space inside each fin is a thin and wide space , for example up to a few mm thick . the chamber 410 and the hollow space inside the fins 405 form a sealed space , and an l - v pcm 403 is provided inside . the l - v pcm has a boiling temperature suitable for the operating temperature range of the led light . examples of materials that can be used as the l - v pcm include water , certain alcohols , etc . a number of led chips 401 are located at the bottom end of the chamber 410 . the chips 401 may be used as chip - area evaporators , shown in detail in fig5 a . in this structure , the led chips 501 a are mounted in the openings of a mounting block 502 a which is about 1 to 5 mm thick . the back surfaces of the chips 501 a and mounting block 502 a , which are exposed to the interior of the chamber 410 , may be treated to be hydrophilic to keep them wet during operation . the back surfaces of the chips 501 a ( about 1 mm 2 in size each ) act as evaporators for phase change heat transfer . alternatively , as shown in fig5 b , the led chips 501 b may be mounted on the underside of a mounting and thermal block 502 b , which has its upper side exposed to the interior of the chamber 410 and acts as an evaporator . comparing with the evaporator shown in fig5 a , the thermal block - area evaporator of fig5 b has a larger evaporating surface which leads to a relatively low thermal power density on the surface of the evaporator . the mounting and thermal block evaporator 502 b may be made of a copper sheet with a thickness of about 1 to 5 mm , but other materials and thicknesses may be used as well . the back surface of the mounting and thermal block evaporator 502 b is treated to be hydrophilic . it can spread the heat from the approximately 1 mm 2 area of the led chip 501 b to a relatively larger evaporating area ( about 1 to 2 cm 2 ). in both kinds of evaporator structures ( fig5 a and 5b ), the evaporator is a part of a 3 - d enclosure that encloses the chamber 410 . in some embodiments , the mounting block 502 a and the mounting and thermal block 502 b can be made integrally with the fin structure 405 . for convenient , both types of structures shown in fig5 a and 5b are referred to as evaporators . the l - v pcm , which is preferably a liquid at room temperature , is placed inside an l - v pcm reservoir 404 , which is located near the evaporator surface in the example shown in fig4 . different methods , including gravitational force , capillary force , and pumping methods can be used to spread the liquid from the reservoir 404 and constantly form a thin layer of liquid 403 on the evaporator surfaces . as mentioned earlier , the upper side of the mounting block 502 a / 502 b and chip 501 a has a hydrophilic surface ; additional wick structure or fiber materials can be implemented to transport the l - v pcms from the reservoir 404 to the evaporator surface by capillary action . during operation , as the evaporator surface temperature rises , which can exceed the boiling temperature of the l - v pcm , the thin liquid layer evaporates to carry away the heat from the evaporator surface . the vapor fills the chamber 410 and the hollow space inside the fins of the fin structure , and condenses back into a liquid on the cold inside surfaces of the 3 - d enclosure 405 , transferring the heat to the cold surface . in fig4 , the up and down pointing arrows schematically indicates the general moving directions of evaporation and condensation , respectively . various methods can be used to return the condensed liquid back to the reservoir to continuously form the thin liquid layer on the evaporator surface . in one design , shown in fig6 a ( cross - sectional view of a part of the fin structure ), the fins 405 a of the fin structure have a tapered shape such that the inside surfaces of the hollow space of the fins are not horizontal . the taper angle may be , for example , 5 - 15 degrees from horizontal . this structure helps the condensed liquid to flow or drip down under gravity ( as schematically indicated by the arrows ) to return to the reservoir 404 and the evaporator surface . in another example , shown in fig6 b , the fins 405 b are still parallel to each other in the cross - sectional view , but the fins tilt upwards as they extend outwards from the chamber . the tilt angle may be , for example , 5 - 15 degrees from horizontal . the liquid can flow downwards and drip down from the inner circular edge of each fin ( as schematically indicated by the arrows ) to return to the reservoir 404 and the evaporator surface . the led light shown in the embodiment of fig4 ( as well as those shown in fig7 - 11 ) is intended to be used in the orientation as shown , i . e ., the mechanical and electrical connector 407 is located at the top and can be screwed into a conventional light fixture , while the led chips 401 are located at a lower part and the light is projected downward though a transparent light cover 402 which faces downward . modifications are needed if the led light is intended to be used in other orientations , e . g ., with the light projecting upwards or laterally to the side . in such cases , the evaporator surfaces ( led chips or mounting block ) will not be located at the bottom of the chamber , but at the top or elsewhere . therefore , a wick structure will be needed to transport the liquid l - v pcm from the bottom of the chamber to the evaporator surfaces . the power unit 406 containing circuitry for driving the led chips can be located at any suitable location . as seen above , a phase change thermal exchange method is used as a thermal transformer to match thermal impedance of a small area of the chip evaporator ( fig5 a ) or mounting and thermal block evaporator ( fig5 b ) and the large arrears of the convection cooled surfaces of the 3 - d enclosure 405 without any solid or liquid connections . since the heat exchange coefficient of evaporation is large enough to transfer the heat without significant temperature rise from an approximately 1 cm 2 area to a much larger area of the 3 - d enclosure 405 , and conventional air / liquid convection methods are sufficient to dissipate the heat from the large areas of 3 - d enclosure 405 without significant temperature rise above the environmental temperature , the total temperature difference between the led device junction and the environment where the heat is dissipated into is small . an led light according to a second embodiment of the present invention is illustrated in fig7 . this structure is useful in the situation that the temperature of the environment is higher than the desired operating temperature of the led chip during the light operation . this structure is similar to that shown in fig4 , where like components are indicated by like symbols : led chips 701 , light cover 702 , l - v pcm 703 , l - v pcm reservoir 704 , fin structure ( 3 - d enclosure ) 705 , power unit 706 , and mechanical and electrical connector 707 . in addition , multiple containers 708 containing a solid to liquid phase change material ( s - l pcm ) 709 are provided in the interior space 710 of the led light . during operation , the heat is transferred by the l - v pcm 703 from the evaporation surfaces ( led chip or the mounting block ) to the surface of containers 708 where it condenses . when the s - l pcm temperature increases to the melting temperature of the s - l pcm , it melts to absorb the heat . thus , the temperature of the evaporation surface ( the led chips or the mounting block ) can be kept nearly constant at slightly above the melting temperature of the s - l pcm 709 . the s - l pcm 709 is selected to have a melting temperature near ( slightly lower than ) the maximum desired operating temperature of the led chip . the s - l pcm containers 708 preferably have small sizes and are shaped as plates or cylinders to increase the contact area between them and the l - v pcm vapor . they can be placed inside the interior space 710 of the led light as shown in fig7 , where the plates or cylinders are arranged vertically so that condensed liquid falls down back to the evaporator and the reservoir . or they can be placed inside a different storage enclosure which is connected to the interior space 710 through a vapor piping via which l - v pcm vapor flows from the interior space 710 to the second enclosure and by a liquid piping via which the condensed liquid of the l - v pcm flows back to the interior space 710 . suitable structures may be used to cycle the liquid and vapor between the two enclosures . using this structure , when the environmental temperature is higher than the melting temperature of the s - l pcm , the heat generated by the led chips during operation is temporarily stored inside the s - l pcm , and then dissipated into the environment when the environmental temperature drops down during the night . four led lights according to third to sixth embodiments of the present invention are shown in fig8 to 11 , respectively . the third embodiment ( fig8 ) and the fifth embodiment ( fig1 ) are modifications of the first embodiment ( fig4 ). the fourth embodiment ( fig9 ) and the sixth embodiment ( fig1 ) are modifications of the second embodiment ( fig7 ) like components are labeled with like symbols and they are not enumerated here . in the first ( fig4 ) and second ( fig7 ) embodiments , the hollow fins in the fin structures 405 / 705 are substantially horizontal structures when the lights are oriented in the way they are intended to be used ( the term substantially horizontal allows for the taper and / or tilt shown in fig6 a and 6b ). for example , each fin may be shaped as an annular disk disposed substantially horizontally parallel to the evaporator surface . in the third to sixth embodiments , the hollow fins of the fin structure 805 / 905 / 1005 / 1105 are substantially vertical structures when the lights are oriented in the way they are intended to be used . for example , the fins may be shaped as concentric nested tubes disposed perpendicular to the evaporator surface , or they may be flat plates disposed in parallel with each other and perpendicular to the evaporator surface . the cycling of the l - v pcm by gravitational mechanism in these embodiments is more convenient because of their vertical hollow fins . in addition , the bottom side of the enclosure 811 / 911 / 1011 / 1111 located under the fins can be slightly slanted toward the center to help the condensed liquid flow into the reservoir 804 / 904 / 1004 / 1104 and the evaporator surface . the different overall geometries of the fin structures ( 3 - d enclosures ) 805 / 905 / 1005 / 1105 shown in fig8 - 11 are suitable for various application environments . the overall shape of the fin structure in the third ( fig8 ) and fourth ( fig9 ) embodiments is a dome , i . e ., the outer fins are shorter than the inner fins , while the overall shape of the fin structure in the fifth ( fig1 ) and sixth ( fig1 ) embodiments is a cylinder . i . e ., the fins have the same height . in the above embodiments , the fins of the fin structures are hollow inside . one advantage of such a structure , compared so the structure with solid fins such as that shown in fig3 , is that it promotes transfer of heat to the surface of the fins because the vapor of the l - v pcm can enter the hollow space inside the fins . another advantage is that it reduces the amount of material ( typically metal , e . g . aluminum ) that needs to be used to make the fin structure . in the conventional structure shown in fig3 , the fins 303 need to have a certain thickness to allow sufficient heat conduction from the base of the fins to the tip of the fins ; therefore , a certain amount of material ( metal ) is required . in the hollow fin structure of the present embodiments , the thickness of the metal sheets of the hollow fins can be as thin as the mechanical strength of the fins will allow , because the heat only needs to be conducted from the inside surface of the fins to the outside surface and does not need to be conducted laterally from the base to the tip of the fins . this reduces the amount of materials required to make the fin structure , and therefore saving material cost and weight . an example of a manufacturing process for the 3 - d vacuum - sealed enclosure 405 / 705 of the first and second embodiment is schematically shown in fig1 and 12a . the fin structure is made of thin metal ( e . g . aluminum ) sheets 1201 formed into required shapes and joined together by a joining structure . to form the fin structure shown in fig4 and 7 , where the fins are horizontal , the metal sheets are made into a flat annular ring shape . to form the tapered or tilted fin structures shown in fig6 a and 6b , the metal plates are made into shallow truncated cone shapes . the metal plates can be made into other suitable shapes depending on the shaped of the fins . as shown in fig1 and 12a , the joining structure includes inner rings 1203 , 1204 and outer rings 1202 which are preferably made of plastic . the outer periphery of every other sheet 1201 ( e . g ., the first , third , fifth , etc .) is sealed to the outer periphery of the sheet under it by an outer sealing ring 1202 , and the space between such pair of sheets will form the hollow space of the hollow fins . the inner rings 1203 , 1204 are interleaved between the sheets at their inner peripheries , forming a stack . the inner rings 1204 which are disposed between two sheets 1201 whose outer peripheries are not sealed together are sealing rings that seal the respective inner peripheries together . the inner rings 1203 which are disposed between two sheets 1201 whose outer peripheries are sealed together are support rings for providing mechanical support to the stack of sheets , and they have openings on them to allow vapor and liquid to flow between the hollow space of the fins and the interior chamber 1205 . note that in fig1 , the inner peripheries of pairs of adjacent sheets whose outer peripheries are not sealed together are joined directly to each other without the support rings 1204 . the rings 1202 , 1203 and 1204 may be adhered to the sheets 1201 using a suitable adhesive material . the fin structure can be assembled by sequentially placing the sheets and the outer and / or inner rings on top of each other and adhering them together to form a stack . compared to forming the entire fins structure form a metal , the above manufacturing method is more cost effective without compromising the heat dissipation performance . the fin structures in the third to sixth embodiments ( fig8 - 11 ) can be formed in a similar manner , using a nested set of cylindrical shaped metal sheets of different diameters and sealing them together with plastic rings at appropriate locations at upped edges and lower edges of the tubes . a pair of adjacent cylindrical sheets sealed together by a sealing ring at their upper edges will form a fin with a hollow space inside , and adjacent fins are sealed to each other by sealing rings located at their lower edges . to summarize , in traditional heat pipes or vapor chambers , the main material is copper . this leads to the high costs of the traditional heat pipes or vapor chambers . in embodiments of the present invention , aluminum sheets can be sealed successfully by using plastic rings . because aluminum is a relatively cheap materials and because of the hollow structures , the estimated cost of such 3 - d enclosures for the high power leds can be as low as 0 . 5 to 1 . 5 dollars . comparing with solid heat sinks or 1 - d / 2 - d heat pipes coupled with solid heat sinks , the 3 - d enclosure according to embodiments of the present invention achieves a relatively low cost and a much better thermal matching performance . it is understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims .