Abstract:
LED lamps may be effectively cooled with an atmosphere of high thermal conductivity. Hydrogen and helium are transparent gases with high thermal conductivity. Enclosing an LED light source in such a gas environment efficiently conducts heat from the LED thereby enhancing the LED&#39;s output and extending the LED&#39;s life.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The Applicant hereby claims the benefit of his provisional application, Serial No. 60/461,956 filed Apr. 10, 2003 for LED Lamp. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The invention relates to electric lamps and particularly to solid-state electric lamps. More particularly the invention is concerned with solid-state electric lamps held in enclosed in an atmosphere.  
           [0004]    2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98  
           [0005]    LEDs are commonly used as light sources in a variety of lamp shapes. In general LEDs have been used as discrete elements, dispersed on an open surface. In this form the surrounding air naturally cools the LEDs. To achieve higher lamp intensity, the LEDs have to be clustered together. This increases the cumulative heat, which leads to the use of an associated heat sink. The size of the heat sink can be difficult accommodate in a lighting system. At the same time the size of heat sink can interfere with the light radiating from the lamp. There is then a need for a lamp with one or more LEDs as light sources that does not use, or can use a significantly smaller heat sink.  
         BRIEF SUMMARY OF THE INVENTION  
         [0006]    An LED lamp may be formed from a solid-state light source mounted on a support structure. A light transmissive envelope encloses the light source and support structure, and an electrical input lead and return lead pass into the envelope providing electrical energy to the light source. A low molecular weight gas fill, such as helium or hydrogen, is enclosed in the envelope to be in thermal contact with the light source. The thermal conductivity of the fill gas cools the LED source and does not interfere with light transmission.  
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 shows a schematic, cross sectional view of an LED lamp. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0008]    The LED lamp  10  comprises a solid-state light source  12  mounted on a support structure  14 . The light source  12  and support structure  14  are enclosed by a light transmissive envelope  16 . Electrical input lead  18  and return lead  20  pass into the envelope  16 , providing electrical energy to the light source  12 . A low molecular weight, thermally conductive cooling gas  22  is enclosed in the envelope  16  to be in thermal contact with the light source  12 .  
         [0009]    The solid-state light source  12  may be an LED or a solid-state laser. Preferably it is a naked chip mounted directly on a thermally conductive support (“chip on board”), and the chip is not coated or sealed by an epoxy or other coating material. The openly exposed light source  12  then has direct contact with the surrounding cooling gas  22 .  
         [0010]    The support structure  14  may comprise metal support rods, or a common stem type support. Given the small size of the LED light source  12  and the relatively large size of the support structure  14 ; the mechanical leverage exerted on the light source  12  may be excessive. The preferred support structure  14  then includes a constraint  24  between the input lead  18  and the return lead  20  so bending and twisting moments between the leads  18 ,  20  are not or are only minimally transmitted through the light source  12 . An electrically insulating bridge, glass rod or stem support may be used. Preferably the mechanical support structure  14  is as thermally conductive as possible. Preferably both the electrical input lead  18  and return lead  20  are highly thermally conductive. Copper or a similarly high thermal conductivity material may be used as the electrical input lead  18  and return lead  20 . The support structure  14  may additionally include cooling features such as fins, plates or extended surfaces that spread or radiate heat over a greater area than simple straight rods. It is understood that large volume rods or similarly large mass, and large surface area supports may be used. The one electrical connector may include a reflector  26  or similarly mirrored body, wherein the reflector  26  also acts as a heat sink and thermal radiator. FIG. 1 shows a naked LED chip mounted on a thermally conductive plate, while two thermally conductive electric leads  18 ,  20  are coupled to the light source  12 , such as an LED chip.  
         [0011]    The light transmissive envelope  16  encloses the light source  12  and support structure  14 . The preferred envelope  16  is made of glass, as it is inexpensive, easily molded into useful shapes, and can contain most low molecular weight gases to a reasonable degree. Preferable the exterior surface area of the envelope  16  is much larger than the surface area of the light source  12 . Preferably the ratio of the exterior surface area of the envelope to the surface area of the light source  12  is greater than the ratio of the light source  12 &#39;s temperature in Celsius to the exterior (ambient) temperature in Celsius, (typically less than 35 degrees Celsius). The envelope  16  interior need not necessarily be a particularly clean environment. It only needs to contain the cooling gas  22  at the preferred pressure. In standard incandescent lamps, it is important to keep water and oxygen away from the hot filament. Epoxies are used to coat the LED in many common constructions, but the epoxies interfere with heat conduction and light projection. The envelope  16  environment need only be as clean as that provided by the epoxy, so as to provide the same relative degree of protection from any infringing water, oxygen or other possibly injurious material. The envelope  16  may be sealed by press sealing as is known in the industry, but it may also be sealed mechanically with a mechanical plug, hardenable cement (silicon rubber, epoxy, saurising cement or similar), coating or similar material to fill to close the a fill gas opening. The seal only needs to retain the cooling gas in place at the preferred pressure. The seal may be a simple plug  28  in the envelope  16 . A press seal, albeit more expensive, is preferred.  
         [0012]    The electrical input lead  18  and return lead  20  pass into the envelope  16  providing electrical energy to the light source  12 . These input lead  18  and return lead  20  may be straight rods sealed to the glass envelope  16  as is typical of a stem type. They may comprise a sealed foil input lead  18  and return lead  20  as is typical of tungsten halogen lamp assemblies. The seal need only be sufficient to reasonably contain the preferred gas  22  filling in the envelope  16 , at a preferred pressure for useful life for the lamp; and to similarly keep injurious material out of the envelope. The choice of a metal lead and the glass envelope  16  is in part a matter of design choice to achieve a sufficiently good seal.  
         [0013]    The thermally conductive gas  22  encloses the envelope  16  in thermal contact with the light source  12 . The preferred gas  22  filling is helium, but it could be hydrogen or other relatively molecularly lightweight gas  22 , meaning a gas with an average molecular weight that is ten percent less than the average molecular weight of air. Helium is approximately seven times more efficient as a heat conducting gas  22 , than is air. For pure heat conduction hydrogen even lighter and more thermally conductive, however can be explosive in some situations, so its use presents a theoretical danger. The preferred pressure is about 0.75×10 5  Pascals to 8.0×10 5  Pascals (0.75 to 8 atmospheres). If the pressure is too low, the fill gas effectively acts as an insulating vacuum, thereby defeating the intended purpose of using the gas  22  to actively conduct heat away from the light source  12 . If the fill pressure is too high, it offers the opportunity for the lamp to fail catastrophically, which is an undesirable result.  
         [0014]    The envelope  16  may be supported by a base  30 . The base  30  includes a mounting to receive and retain the envelope  16 . The base  30  additionally includes one or more channels for receiving the exterior ends of the input lead  18  and the return lead  20 . The leads  18 ,  20  are connected to the contacts as electrically isolated contact points for electrical connection in a correspondingly formed socket. The base  30  may be a pin, threaded, wedge or similarly shaped socket and may even be configured to fit existing sockets. Conforming the incoming power to that needed by the one or more LED&#39;s may require circuitry  32  as is known in the art that may be enclosed in the base  30 . For example the base  30  may have a threaded base  30  with contacts typical of a threaded miniature bulb, for example one used in a flashlight. Adapting the gas filled envelope to the various bases (threaded, pin, wedge, bayonet, etc.) and sockets is considered to be within the skill in the art of lamp making.  
         [0015]    It is understood that the use of only one solid state light source has been shown, a plurality may be mounted in the gas filled envelope, and that the gas cooling effect is more relevant where the number of sources is high or they are closely mounted so as to have a relatively high heat source density. While there have been shown and described what are at present considered to be the preferred embodiments of the invention, it will be apparent to those skilled in the art that various changes and modifications can be made herein without departing from the scope of the invention defined by the appended claims.