LED illumination devices
A lens element has a curved surface mounted adjacent an LED for improving the light transmission efficiency and the dispersal pattern of radiation emitted by the LED.
This application claims benefit under 35 USC Sections 119(e) and 120 to the filing date of U.S. Provisional Application Ser. No. 60/652,317 filed by Mark S. Olsson on Feb. 10, 2005.
FIELD OF THE INVENTIONThe present invention relates to lighting, and more particularly, to illumination devices that use light emitting diodes (LEDs) as a source of light.
BACKGROUND OF THE INVENTIONSemiconductor LEDs have replaced conventional incandescent, fluorescent and halogen light sources in many applications due to their small size, reliability, relatively inexpensive cost, long life and compatibility with other solid state devices. In a conventional LED, an N-type gallium arsenide substrate that is properly doped and joined with a P-type anode will emit light in visible and infrared wavelengths under a forward bias. In general, the brightness of the light given off by an LED is contingent upon the number of photons that are released by the recombination of carriers inside the LED. The higher the forward bias voltage, the larger the current and the larger the number of carriers that recombine. Therefore, the brightness of an LED can be increased by increasing the forward voltage. However due to many limitations, including the ability to dissipate heat, conventional LEDs are only capable of producing about six to seven lumens.
Recently a new type of LED has been developed for use as a flash in camera phones. The Luxeon® Flash LXCL-PWF1 and LXCL-PWF2 LEDs commercially available from Lumileds Lighting of San Jose, Calif., USA are capable of producing forty lumens at one ampere, and eighty lumens at one ampere, respectively. These surface mounted LEDs are only one millimeter in height and they have a very small footprint (2.0×1.6 mm or 3.2×1.6 mm, respectively). They are rated for 100,000 flashes at one ampere, and one hundred and sixty-eight hours of DC (flashlight/torch mode) at 350 milliamperes.
While these new flash LEDs offer increased brightness over conventional LEDs they still suffer from problems associated with heat dissipation and inefficient distribution of light.
SUMMARY OF THE INVENTIONIn accordance with an embodiment of the invention an illumination device includes an LED and a lens element with a curved surface positioned opposite a light emitting surface of the LED. A quantity of transparent material joins the lens element and the light emitting surface of the LED.
In accordance with another embodiment of the invention an illumination device includes at least one LED mounted on a substrate and having an exposed metal heat conduction surface. At least one aperture is formed in the substrate adjacent to the exposed metal heat conduction surface of the LED and a heat sink is mounted in the aperture.
In accordance with another embodiment of the invention a method of fabricating an illumination device includes the steps of removing a top section of an optically transparent cover of a high intensity LED package and leaving a remaining lower section having a height dimension less than about twice a longest dimension of a light emitting surface of an LED in the LED package. The method further includes the step of mounting a lens element on top of the lower section, the lens element having a curved surface that faces the light emitting surface of the LED.
BRIEF DESCRIPTION OF THE DRAWINGSThroughout the drawing figures, like numerals refer to like parts.
The entire disclosure of Provisional Application Ser. No. 60/652,317 of Mark S. Olsson filed Feb. 10, 2005, is hereby incorporated by reference.
Referring to
Besides sapphire, transparent ceramics such as Magnesia (MgO), magnesium aluminate spinel (Mg Al2O4), aluminum oxynitride spinel (AlON), cubic zirconia (ZRO2Si), spinel (MgO×Al2O3) and rutile (TiO2) can also be used for the transparent element 12 due to their a high thermal conductivity. It is preferable that the transparent element 12 be made of a material that has at least half or more of the thermal conductivity of sapphire. Sapphire has an additional advantage of having a high index of refraction, such that when element 12 is made of properly shaped sapphire, it can focus the radiation emitted by the flash LED 10 into a highly useful slightly diverging beam
Heat transfer is improved by using a body 16 of an optically transparent material to thermally couple the flash LED 10 and the transparent element 12. The body 16 may be transparent fluid, grease, gel or polymer. One suitable material is DOW CORNING® compound 4 (DC 4) which is stable up to four hundred degrees F (204 C.) which is above the maximum operating temperature of the flash LED 10. Certain fluorocarbon thermal management fluids such as 3M Novec® Engineered Fluids (HFE-7200) or 3M Fluorinertg Electronic Liquids. HFE-7000 has a boiling point of 76 C., which is well below the operating temperature of the flash LED 10. Boiling off of the cooling fluid, on and adjacent to the flash LED 10 can provide significant additional cooling. For additional cooling forced fluid flow and channels can be provided adjacent the flash LED 10. The flash LED 10 and body 16 can be pressed against the base of the transparent element 12 with a spring or using the resilience of the PCB 14, as indicated by the arrows 18.
A low melting point metal could also be used as a heat conducting element all around the sides of the flash LED 10. Metals such as bismuth or gallium with a melting point well below the maximum operating temperature of the flash LED 10 can be used. Among these are ten specialty solders commercially available from Indium Corporation of America having melting points below 140 degrees C.
Another aspect of the present invention involves press fitting a sapphire sphere or a modified sapphire sphere into a surrounding metal structures. High thermal conductivity metals such as copper, brass, bronze and aluminum are particularly suitable in this application, but other metals such as stainless steel and titanium may suffice in particular environments. A press fit provides an optimal thermal coupling between the sapphire element and the metal structure. The metal structure may be in thermal contact with other structures to provide greater heat sink capabilities. Referring now to
While press fitting the sapphire sphere has certain advantages, it is not essential to the present invention. Other means for holding the transparent element 12 in place can be used, be they mechanical or adhesive. A thermal shrink fit can also be employed. By way of example only, mounting a sapphire sphere 12 in a bore in an aluminum alloy (7075, 6061 or 6262) or brass alloy (CA 360 ) with a press fit of about one percent smaller than the diameter of the pressed sphere has produced good results. With softer materials press fits as high as two percent have been successful.
In the embodiment of
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A further aspect of the present invention involves the use of the anodized coating as an electrical insulating layer between the conductive traces 96 on the PCB 14 and the anodized aluminum face plate 92. Bare, large surface area conductors can be used on the LED side of the PCB 14 and held in mechanical contact with the insulating surface of the face plate 92 to maximize thermal contact. The anodized layers 90 can be made very thin and therefore provide very good thermal conductors. The thermal grease 16 provides even further heat transfer efficiency. Extra thick copper traces 96 can further enhance heat extraction.
Conventional techniques to remove backside heat from the PCB 14 can also be used in addition to those illustrated. The efficiency and operating life of the flash LED 10 are improved if its operating temperature can be reduced. Conventional techniques include heavy copper traces, metal cores in the PCB 14, the inclusion of thermal vias, thermal fillers (T-Lam), multi-layer PCBs with copper flood planes, and conventional heat sinks.
Referring to
The shape of the beam formed by the transparent element 12 can be adjusted by various means. Where the transparent element 12 is a sapphire sphere and mounted completely or partially in a socket or recess in a front plate such as 80, the region above the transparent element 12 can be filled with a transparent compound. If this compound has a flat outer surface the beam will be spread into a wider, less focused beam. The higher the index of refraction of the potting material, the less focused, and hence the wider the beam will be. Alternately, a polished flat or facet can be ground or otherwise formed on the upper side of the sapphire sphere 12 before installation into the face plate 80. Generally, although not necessarily, the plane of this facet would be parallel with the outer plane of the face plate 80. The facet could be a small area at the apex of the sapphire sphere or a much larger facet if the sapphire is a hemisphere. The larger the area of the facet, the less focused the beam will be. The upper and/or lower surfaces of the transparent element 12 could be frosted by chemical etching or mechanical techniques such as sandblasting to diffuse and soften the beam. The lower apex of the transparent element 12 can be ground or polished to provide a small facet having an area that is approximately the same as the emitter area of the flash LED. In general, it has been found that larger diameter sapphire spheres provide higher optical coupling efficiencies (brighter beams) and smaller sapphire spheres produce more tightly focused beams. It is preferable to remove the reverse voltage protection die on the flash LED 10 in order to achieve maximum thermal coupling.
Over a range of about thirty to forty-five degrees, from the normal (Z-axis) to the face plate 80, the beam can be steered simply by laterally shifting (in X and Y) the position of the flash LED 10 relative to the central axis of the bore in the face plate 80. This results in greater de-focusing and an increasing separation between the sapphire sphere 12 and the flash LED 10. This may impair heat transfer, but this can be offset by introducing a component of Z axis movement in combination with X-Y scanning to keep the flash LED 10 as close as possible to the surface of the sapphire sphere 12.
Referring to
A pair of oppositely wound, flat spiral springs (not illustrated) can provide compliant mounting force needed to hold the flash LED 10 against the sapphire sphere 12, while at the same time providing an electrical connection to the PCB 14.
A larger sapphire sphere could be combined with a plurality of flash LEDs 10 (not illustrated) mounted in an array on one hemisphere or a section of the hemisphere. The beam projected from each flash LED may or may not overlap the beam from an adjacent LED 10.
RGB arrays of flash LEDs 10 can be employed to allow multi-colored beams to be produced. While presently only available in white, it is anticipated that flash LEDs of the type identified herein will be available that emit light in various colors. The phosphor coating on the commercially available flash LED 10 can be removed after SMT to PCB to produce a blue light emitting device.
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The embodiment 180 of
The high intensity LED and lens assemblies of
The spherical lens element may also be made of Cubic Zirconia with a high index of refraction, such as N=2.17. Whereas a spherical sapphire lens may create some secondary rings of light in the beam outside of the main central focus, the beam produced by a spherical lens element made of high index of refraction Cubic Zirconia is much cleaner. The Cubic Zirconia spherical lens element produces a high efficiency beam of light with superior control. More particularly, the use of such a Cubic Zirconia spherical lens element with a high lumen LED produces a focused convergent beam that allows one to easily add a molded plastic optic to collimate or diverge the beam to essentially any beam angle from a narrow spot to a wide flood.
Regardless of what material the spherical lens element is made of, preferably the surface of the spherical lens element is mounted adjacent the light emitting surface of the LED no further than twice the longest dimension of the light emitting surface. In addition, the spherical lens element should have an index of refraction relative to the light emitted by the high lumen LED greater than about 1.65. Moreover, excellent results can be achieved by using a spherical lens element having a diameter D greater than about three times the longest dimension of the light emitting surface. The light path optical space between the spherical lens element and the light emitting surface of the adjacent high lumen LED is preferably filled with an intervening optically transparent material selected from the group consisting of fluid, gel, elastomer or rubber-like material, having an index of refraction less than about 1.50.
A high index of refraction lens element material is particularly suited for underwater lighting applications using LED light sources, where, for example, N should be greater than about 1.6. When a spherical lens element is submerged in a fluid or plotting compound its refractive power is greatly reduced and therefore, the spherical lens element should be made of a material having a much higher index of refraction. A high index of refraction material is needed when a rear or lower side of a spherical lens element is pressed against silicone gel or other interface material covering the face of the LED.
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The substrate 216 (
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The thru-hull illumination device 262 (
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While various embodiments of improved LED illumination devices have been described in detail, it will be apparent to those skilled in the art that the invention can be modified in both arrangement and detail. For example, the lens element that directly gathers light from the high intensity LED 204 can have varying shapes and configurations; however, preferably the underside surface is round, ellipsoid, parabolic or some other curved surface for gathering the light. As another example, the embodiments of
Claims
1. An illumination device, comprising:
- an LED;
- a lens element with a curved surface positioned opposite a light emitting surface of the LED; and
- a quantity of transparent material joining the lens element and light emitting surface of the LED.
2. The illumination device of claim 1 and further comprising a second lens element mounted adjacent the lens element positioned opposite the light emitting surface of the LED.
3. The illumination device of claim 1 wherein the lens element is made of Cubic Zirconia.
4. The illumination device of claim 1 wherein a distance between a light emitting surface of the LED and the curved surface of the lens element is less than about two times a longest dimension of the light emitting surface of the LED.
5. The illumination device of claim 1 wherein the lens element is generally spherical and has a diameter greater than about three times a longest dimension of a light emitting surface of the LED.
6. The illumination device of claim 1 wherein the lens element has an index of refraction greater than about 1.65 and the silicone gel has an index of refraction less than about 1.50.
7. An illumination device, comprising:
- a substrate;
- a least one LED mounted on the substrate and having an exposed metal heat conduction surface;
- at least one aperture formed in the substrate adjacent to the exposed metal heat conduction surface of the diode; and
- a heat sink mounted in the aperture.
8. The illumination device of claim 7 and further comprising a clamp structure for biasing the metal heat conduction surface against the heat sink.
9. A method of fabricating an illumination device, comprising the steps of:
- removing a top section of an optically transparent cover of a high intensity LED and lens assembly leaving a remaining lower section having a height dimension less than about twice a longest dimension of a light emitting surface of the LED; and
- mounting a lens element on top of the lower section, the lens element having a curved surface that faces the light emitting surface of the LED.
10. The method of claim 9 and further comprising the step of leaving a sufficient amount of transparent silicone gel to serve as an optical interface joining the light emitting surface and the generally spherical lens element.
11. An illumination device, comprising:
- a light emitting diode;
- a generally spherical lens mounted adjacent to a light emitting surface face of the light emitting diode and positioned no further away from the light emitting surface than twice the longest dimension of the light emitting surface;
- the spherical lens having an index of refraction relative to light emitted by the diode greater than about 1.65;
- the spherical lens having a diameter greater than three times the longest dimension of the light emitting surface; and
- a space between the spherical lens and the light emitting surface being filled with an intervening optically transparent material selected from the group consisting of fluid, grease, gel and elastomer having an index of refraction less than about 1.50.
12. The illumination device of claim 11, wherein the spherical lens is made of Cubic Zirconia.
13. The illumination device of claim 11, wherein the spherical lens is made of Sapphire.
14. The illumination device of claim 11, wherein the spherical lens is made of SF8 Optical Glass.
15. The illumination device of claim 11, wherein the intervening optically transparent material is silicone gel.
16. The illumination device of claim 11, wherein the intervening optically transparent material is silicone rubber.
17. The illumination device of claim 11 wherein the spherical lens is press fit into a thermally conductive metal support structure.
18. An illumination device, comprising:
- a substrate;
- a light emitting diode having an exposed metal heat conduction surface mounted on the substrate;
- an aperture formed in the substrate adjacent to the metal heat conduction surface; and
- heat sink means extending through the aperture for dissipating heat from the exposed diode metal heat conduction surface.
19. The illumination device of claim 18 wherein the heat sink means is made of anodized Aluminum.
20. The illumination device of claim 18 wherein the heat sink means is made of a material selected from the group consisting of Copper and Copper alloy.
21. The illumination device of claim 18 wherein the heat sink means is made of an insulated Copper alloy.
22. The illumination device of claim 18 wherein the heat sink means is made of a Copper alloy insulated with a diamond film.
23. The illumination device of claim 18 and further comprising means for clamping the metal heat conduction surface against the heat sink means.
24. The illumination device of claim 18 wherein the heat sink means includes an anodized Aluminum pin press fit into a second heat sink.
25. The illumination device of claim 18 wherein the metal heat sink means includes an anodized Aluminum pin that extends into the aperture.
26. An illumination device, comprising:
- a surface mounted light emitting diode with an exposed metal heat conduction surface;
- a heat sink; and
- a spring clamp for holding the metal heat conduction surface against the heat sink.
27. The illumination device of claim 26 wherein the spring clamp includes a metal disc spring.
28. The illumination device of claim 26 wherein the spring clamp includes a Beryllium Copper metal disc spring.
29. A illuminated device, comprising:
- a light emitting diode;
- a generally spherical lens element mounted adjacent to a light emitting surface of the light emitting diode;
- the spherical lens element having an index of refraction relative to light emitted by the diode that is greater than about 1.65; and
- a side of the spherical lens element opposite the light emitting surface being in contact with an optically transparent material with an index of refraction greater than about 1.20.
30. The illumination device of claim 29 wherein the optically transparent material is water.
31. The illumination device of claim 29 wherein the optically transparent material is mineral oil.
32. The illumination device of claim 29 wherein the optically transparent material is a 3M Fluorinert™ fluid.
33. The illumination device of claim 29 wherein the optically transparent material is a 3M Novec™ fluid.
34. The illumination device of claim 29 wherein the optically transparent material is silicone rubber.
35. The illumination device of claim 29 wherein the optically transparent material is silicone grease.
36. The illumination device of claim 29 wherein the optically transparent material is polyurethane rubber.
37. An illumination device, comprising:
- a light emitting diode;
- a spherical lens element mounted adjacent a light emitting surface of the light emitting diode;
- the spherical lens element having an index of refraction relative to light emitted by the diode of greater than about 1.80; and
- a negative focal length optical element placed in front of the spherical lens element to form the light into a beam having a predetermined shape.
38. The illumination device of claim 37 wherein the negative optical element has a prismatic component to redirect the light beam off axis.
39. The illumination device of claim 37 wherein the negative focal length optical element has a cylindrical component to change an aspect ratio of the light beam.
40. A method of constructing an illumination device, comprising the steps of:
- cutting off a section of an optically transparent cover that encapsulates a light emitting diode, leaving a remaining section above a light emitting surface of the diode no greater than twice the longest dimension of the light emitting surface; and
- mounting a generally spherical Cubic Zirconia lens element having an index of refraction relative to the diode emitted light greater than about 1.65, and having a diameter greater than about three times the longest dimension of the light emitting surface.
41. The method of constructing an illumination device of claim 40 wherein the optically transparent cover is made of silicone rubber.
42. The method of constructing an illumination device of claim 40 wherein the optically transparent cover is made of a silicone rubber dome-like cover that encloses a silicone gel filled volume surrounding the light emitting diode.
43. A method of controlling the output light pattern of a light emitting diode source, comprising the steps of:
- using a Cubic Zirconia spherical lens element to converge the light from a light emitting diode; and
- using a second diverging optical element to diverge the light by a predetermined amount.
44. The method of claim 43 wherein the diverging optical element is a molded transparent plastic.
45. The method of claim 43 wherein the diverging optical element is a molded acrylic plastic.
46. The method of claim 43 wherein an aperture of predetermined size is placed between the Cubic Zirconia spherical lens element and the second diverging optical element to remove light from the edges of the beam.
47. The method of claim 43 wherein a space between the spherical lens element and the diverging optical element is filled with a transparent incompressible material selected from the group consisting of fluid, grease, gel, elastomer and rubber-like material.
48. The method of claim 46 wherein a space between the spherical lens element and the diverging optical element is filled with a transparent incompressible material from the group of fluid, grease, gel or elastomer or rubber-like material.
49. An illumination device, comprising:
- a light emitting diode;
- a generally spherical lens element mounted adjacent a light emitting surface face of the light emitting diode and placed no further away from said light emitting surface than about twice the longest dimension of said light emitting surface;
- the spherical lens element having an index of refraction relative to light emitted by the diode of greater than about 1.80 to converge the light to a focus;
- the spherical lens element having a diameter greater than about three times the longest dimension of the light emitting surface;
- a light path optical space between the spherical lens element and the light emitting surface being filled with an intervening optically transparent material selected from the group consisting of fluid, grease, gel elastomer and rubber-like material having an index of refraction less than about 1.60; and
- an aperture placed approximately at a plane of focus smaller than a diameter of the spherical lens.
50. The illumination device of claim 49 wherein the spherical lens element is made of Cubic Zirconia.
51. An illumination device, comprising:
- a light emitting diode;
- a generally spherical lens element mounted adjacent to a light emitting surface face the light emitting diode and placed no further away from the light emitting surface than about twice a longest dimension of the light emitting surface;
- the spherical lens element having an index of refraction relative to light emitted by the diode greater than about 1.80 to converge the light to a focus;
- the spherical lens element having a diameter greater than about three times the longest dimension of the light emitting surface;
- a light path optical space between the spherical lens element and the light emitting surface being filled with an intervening optically transparent material selected from the group consisting of fluid, grease, gel, elastomer or rubber-like material having an index of refraction less than about 1.60; and
- a spacer to set the distance between the spherical lens element and the light emitting surface to a predetermined distance.
52. The illumination device of claim 51 wherein the inside surface of the spacer is reflectorized.
Type: Application
Filed: Feb 9, 2006
Publication Date: Aug 24, 2006
Inventor: Mark Olsson (La Jolla, CA)
Application Number: 11/350,627
International Classification: F41G 1/34 (20060101);