Thermally efficient LED bulb

[0001] This invention relates to light sources and more particularly to solid-state light sources. Still more particularly it relates to solid-state light sources that can be employed with a reflector to mimic the light distribution of an incandescent light. Still more particularly, it relates to solid-state light sources useable as direct replacements for automotive signal lighting, such as taillights and to such light sources having a viable heat transfer mechanism.

[0002] Solid-state lighting, for example, light emitting diodes (hereinafter, LED) are renowned for their long life and their ability to resist shock. They have been used for some time as the high-mount stop light in automobiles, where no particular amplification or reflection of the light is needed. Attempts have been made in the past to adapt LEDs for other purposes such as taillight units; however, these attempts have applied LEDs typically encased in plastic beads to flat surfaces, which were then ganged on the cylindrical end of, for example, a bayonet base. Little or no light was directed to the reflector for proper light distribution. For the most part, these devices do not meet Federal regulations. Further, it has been found necessary to greatly multiply the number of individual LED units to increase the light output to meet Federal regulations; however, this increase in number has also increased the amount of heat generated and this excess heat has a deleterious effect on the lamp employing the LEDs.

[0003] It is, therefore, an object of the invention to obviate the disadvantages of the prior art.

[0004] It is another object of the invention to enhance LED light sources.

[0005] It is yet another object of the invention to provide an LED light source that can be used as an after-market replacement for existing incandescent lamps.

[0006] These objects are accomplished, in one aspect of the invention by the provision of a solid-state light source compatible with existing sockets normally reserved for filamented lamps that comprises a hollow base formed to mechanically and electrically adapt to a socket and a sub-assembly adapted to cooperate with and fit into the hollow base. The sub-assembly comprises a metal core having a bulbous body and a narrow foot depending therefrom. A circuit board substantially surrounds the metal core on two sides. The circuit board has a bulbous body positioned about the bulbous body of the metal core and it has two spaced apart legs lying adjacent either side of the narrow foot. A plurality of solid-state light sources is mechanically and electrically connected to one side of the circuit board and external electrical contacts are positioned on the circuit board for connection to an electrical circuit. A glass dome covers the bulbous body of the circuit board and metal core and is sealed to the hollow base.

[0007] This construction allows for multiple solid-state devices to be employed to insure adequate light output and the metal core provides adequate heat removal.

[0013] For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims taken in conjunction with the above-described drawings.

[0014] Referring now to the drawings with grater particularity, there is shown in FIG. 1 a solid-state light source 10 compatible with existing sockets normally reserved for filamented lamps. The light source 10 comprises a hollow base 12 formed to mechanically and electrically adapt to a socket. The base 12 is preferably formed of plastic; however, in the event that additional heat dissipation is required, metal, with suitable insulating features, can be employed. A sub-assembly 14 that is adapted to cooperate with and fit into the hollow base 12 comprises a metal core 16 having a bulbous body 18 and a narrow foot 20 depending therefrom. The metal core 16 is preferably made from solid copper; however, other metals can be used, for example, aluminum will function as the core and can be used if weight is a concern. A circuit board 22 substantially surrounds the metal core 16 on two sides. The circuit board 22 has a bulbous body portion 24 that is positioned about the bulbous body 18 of the metal core 16 and has two spaced apart legs 26, 28 lying adjacent either side of the narrow foot 20. The board 22 is preferably formed from a flexible printed circuit board material capable of sustaining a bend radius of at least 0.25 inches (6 mm). For the primary benefits to be obtained, the circuit board 22 must be positioned around the metal core 16 to be in good thermal contact to conduct the heat generated by the LEDs away. For this purpose a thermal glue or paste can be employed between the board and the core.

[0015] A plurality of solid-state light sources 30, for example, light emitting diodes (LEDs) are mechanically and electrically connected to one side of the circuit board by suitable electrically conductive traces, not shown. External electrical contacts 32 are positioned on the circuit board 22 on the legs 26, 28, for connection to an electrical circuit via a suitable socket, into which the light source 10 will be inserted. A glass dome 34 covers the sub-assembly 14 after it is inserted into the hollow base 12 and is sealed thereto. While any suitable glass can be employed it is preferred that the glass be an efficient radiator for infrared emissions. Such a glass is alumina silicate.

[0016] To further aid in the elimination of generated heat, a thermally efficient fluid can fill the interior of the dome. Such a thermally efficient fluid can be a gas, such as hydrogen or helium, a liquid such as silicon, or a vacuum.

[0017] The sides 36 of the metal core 16 not covered by the circuit board 22 can be provided with heat radiating ribs 38. The heat radiating ribs have large exposures going sideways from the lamp providing a large heat-radiating surface.

[0018] The hollow base 12 includes a locking receptacle 40 and depending arms 50, 52 that cover the edges 54, 56 of the narrow foot 20 when the sub-assembly 14 is placed in the base 12. The metal core 16 includes a matching lock 42 for engaging the locking receptacle 40.

[0019] At least one of the legs 26, 28 (preferably, both legs) of the circuit board 22 is provided with a latch 44 and the hollow base 12 has a latch receiver 58 to mate therewith.

[0020] The color emission of the LEDs will be chosen to be suitable for the ultimate purpose of the light source. For example, if the light source is designed for use as a taillight for an automobile, re emitting LEDs will be used. A mix of red, green and blue light emitting LEDs can generate white light

[0021] There is thus provided a solid-state light source that is acceptable for use as an automobile taillight, as original equipment or as a replacement item.

[0022] While there have been shown and described what are 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 as defined by the appended claims.