INTEGRATED LED BASED ILLUMINATION DEVICE
A light emitting diode (LED) based illumination device include a plurality of LEDS mounted to mounting board and includes a transmissive plate disposed above the LEDs. The transmissive plate includes an amount of wavelength converting material configured to change a wavelength of an amount of light emitted by the plurality of LEDs. A base reflector structure is coupled to the LED mounting board and the transmissive plate between at least two of the LEDs. In another configuration, a dam of reflective material surrounds the LEDs and is coupled to the LED mounting board and the transmissive plate, while a dam of thermally conductive material surrounds the dam of reflective material. In another configuration, the LED mounting board has a protrusion of thermally conductive material that surrounds the LEDs and is coupled to the transmissive plate, and has a void on the side opposite the protrusion.
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This application claims priority under 35 USC §119 to U.S. Provisional Application No. 61/697,712, filed Sep. 6, 2012, and U.S. Provisional Application No. 61/790,887, filed Mar. 15, 2013, both of which are incorporated by reference herein in their entireties.
TECHNICAL FIELDThe described embodiments relate to illumination modules that include Light Emitting Diodes (LEDs).
BACKGROUNDThe use of light emitting diodes in general lighting is still limited due to limitations in light output level or flux generated by the illumination devices. Illumination devices that use LEDs also typically suffer from poor color quality characterized by color point instability. The color point instability varies over time as well as from part to part. Poor color quality is also characterized by poor color rendering, which is due to the spectrum produced by the LED light sources having bands with no or little power. Further, illumination devices that use LEDs typically have spatial and/or angular variations in the color. Additionally, illumination devices that use LEDs are expensive due to, among other things, the necessity of required color control electronics and/or sensors to maintain the color point of the light source or using only a small selection of produced LEDs that meet the color and/or flux requirements for the application.
Consequently, improvements to illumination device that uses light emitting diodes as the light source are desired.
SUMMARYA light emitting diode (LED) based illumination device include a plurality of LEDS mounted to mounting board and includes a transmissive plate disposed above the LEDs. The transmissive plate includes an amount of wavelength converting material configured to change a wavelength of an amount of light emitted by the plurality of LEDs. A base reflector structure is coupled to the LED mounting board and the transmissive plate between at least two of the LEDs. In another configuration, a dam of reflective material surrounds the LEDs and is coupled to the LED mounting board and the transmissive plate, while a dam of thermally conductive material surrounds the dam of reflective material. In another configuration, the LED mounting board has a protrusion of thermally conductive material that surrounds the LEDs and is coupled to the transmissive plate, and has a void on the side opposite the protrusion.
Further details and embodiments and techniques are described in the detailed description below. This summary does not define the invention. The invention is defined by the claims.
Reference will now be made in detail to background examples and some embodiments of the invention, examples of which are illustrated in the accompanying drawings.
As depicted in
Light generated by LEDs in the LED based illumination device 100, is generally color converted to generate a desirable output light. Various embodiments are introduced herein to improve the light extraction efficiency from LED based illumination device 100 and to improve the dissipation of heat generated by the color conversion process. In one aspect a base reflector structure (shown in
As depicted in
As illustrated in
As depicted in
Base reflector structure 171 may have a high thermal conductivity to minimize thermal resistance. By way of example, base reflector structure 171 may be made with a highly thermally conductive material, such as an aluminum based material that is processed to make the material highly reflective and durable. By way of example, a material referred to as Miro®, manufactured by Alanod, a German company, may be used.
The optical surfaces of base reflector structure 171 may be treated to achieve high reflectivity. For example the optical surface of base reflector structure 171 may be polished, or covered by one or more reflective coatings (e.g., reflective materials such as Vikuiti™ ESR, as sold by 3M (USA), Lumirror™ E60L manufactured by Toray (Japan), or microcrystalline polyethylene terephthalate (MCPET) such as that manufactured by Furukawa Electric Co. Ltd. (Japan), a polytetrafluoroethylene PTFE material such as that manufactured by W.L. Gore (USA) and Berghof (Germany)). Also, highly diffuse reflective coatings can be applied to optical surfaces of base reflector structure 171. Such coatings may include titanium dioxide (TiO2), zinc oxide (ZnO), and barium sulfate (Ba5O4) particles, or a combination of these materials.
In some embodiments, base reflector structure 171 may be constructed from or include a reflective, ceramic material, such as ceramic material produced by CerFlex International (The Netherlands). In some embodiments, portions of any of the optical surfaces of base reflector structure 171 may be coated with a wavelength converting material.
As illustrated in
In another aspect, a shaped lens element is optically coupled to LEDs 102 and thermally coupled to LED mounting board 104. The shaped lens element may include at least one wavelength converting material. In this manner, light extraction efficiency is improved by the shaped lens element and heat generated by the wavelength converting material on the shaped lens element has a direct thermal path to a heat sinking device.
LEDs 102 can emit different or the same colors, either by direct emission or by phosphor conversion, e.g., where phosphor layers are applied to the LEDs as part of the LED package. The illumination device 100 may use any combination of colored LEDs 102, such as red, green, blue, amber, or cyan, or the LEDs 102 may all produce the same color light. Some or all of the LEDs 102 may produce white light. In addition, the LEDs 102 may emit polarized light or non-polarized light and LED based illumination device 100 may use any combination of polarized or non-polarized LEDs. In some embodiments, LEDs 102 emit either blue or UV light because of the efficiency of LEDs emitting in these wavelength ranges. The light emitted from the illumination device 100 has a desired color when LEDs 102 are used in combination with wavelength converting materials on transmissive plate 174 or shaped lens 172, for example. By tuning the chemical and/or physical (such as thickness and concentration) properties of the wavelength converting materials and the geometric properties of the coatings on the surfaces of transmissive plate 174 or shaped lens 172, specific color properties of light output by LED based illumination device 100 may be specified, e.g., color point, color temperature, and color rendering index (CRI).
For purposes of this patent document, a wavelength converting material is any single chemical compound or mixture of different chemical compounds that performs a color conversion function, e.g., absorbs an amount of light of one peak wavelength, and in response, emits an amount of light at another peak wavelength.
By way of example, phosphors may be chosen from the set denoted by the following chemical formulas: Y3Al5O12:Ce, (also known as YAG:Ce, or simply YAG) (Y,Gd)3Al5O12:Ce, CaS:Eu, SrS:Eu, SrGa2S4:Eu, Ca3(Sc,Mg)2Si3O12:Ce, Ca3Sc2Si3O12:Ce, Ca3Sc2O4:Ce, Ba3Si6O12N2:Eu, (Sr,Ca)AlSiN3:Eu, CaAlSiN3:Eu, CaAlSi(ON)3:Eu, Ba2SiO4:Eu, Sr2SiO4:Eu, Ca2SiO4:Eu, CaSc2O4:Ce, CaSi2O2N2:Eu, SrSi2O2N2:Eu, BaSi2O2N2:Eu, Ca5(PO4)3Cl:Eu, Ba5(PO4)3Cl:Eu, Cs2CaP2O7, Cs2SrP2O7, Lu3Al5O12:Ce, Ca8Mg(SiO4)4Cl2:Eu, Sr8Mg(SiO4)4Cl2:Eu, La3Si6N11:Ce, Y3Ga5O12:Ce, Gd3Ga5O12:Ce, Tb3Al5O12:Ce, Tb3Ga5O12:Ce, and Lu3Ga5O12:Ce.
In one example, the adjustment of color point of the illumination device may be accomplished by adding or removing wavelength converting material from transmissive plate 174 or shaped lens 172, which similarly may be coated or impregnated with one or more wavelength converting materials. In one embodiment a red emitting phosphor 181 such as an alkaline earth oxy silicon nitride covers a portion of transmissive plate 174 or shaped lens 172, and a yellow emitting phosphor 180 such as YAG covers another portion of transmissive plate 174 or shaped lens 172, as illustrated in
In some embodiments, the phosphors are mixed in a suitable solvent medium with a binder and, optionally, a surfactant and a plasticizer. The resulting mixture is deposited by any of spraying, screen printing, blade coating, jetting, or other suitable means. By choosing the shape and height of the transmissive plate 174 or shaped lens 172, and selecting which portions of transmissive plate 174 or shaped lens 172 will be covered with a particular phosphor or not, and by optimization of the layer thickness and concentration of a phosphor layer on the surfaces, the color point of the light emitted from the device can be tuned as desired.
In one example, a single type of wavelength converting material may be patterned on a portion of transmissive plate 174 or shaped lens 172. By way of example, a red emitting phosphor 181 may be patterned on different areas of the transmissive plate 174 or shaped lens 172 and a yellow emitting phosphor 180 may be patterned on other areas of transmissive plate 174 or shaped lens 172. In some examples, the areas may be physically separated from one another. In some other examples, the areas may be adjacent to one another. The coverage and/or concentrations of the phosphors may be varied to produce different color temperatures. It should be understood that the coverage area of the red and/or the concentrations of the red and yellow phosphors will need to vary to produce the desired color temperatures if the light produced by the LEDs 102 varies. The color performance of the LEDs 102, red phosphor and the yellow phosphor may be measured and modified by any of adding or removing phosphor material based on performance so that the final assembled product produces the desired color temperature. In some examples, the color of an assembled LED based illumination device is measured after final assembly and an appropriate change in phosphor content to reach the desired color temperature is determined based on the measured color. The appropriate change in phosphor content can be realized by either removing phosphor material (e.g., laser ablation, mechanical abrasion, etc.) or by adding phosphor material (e.g., by any of spraying, screen printing, blade coating, jetting, etc.). In some other examples, the color of an LED based illumination device is measured before final assembly. The appropriate change in phosphor content can be realized by either removing phosphor material or by adding phosphor material to the transmissive plate 174 or shaped lens 172. After changing the phosphor content, the LED based illumination device 100 undergoes final assembly where the transmissive window 174 or shaped lens 172 is permanently fixed into position.
Transmissive plate 174 and shaped lens 172 may be constructed from a suitable optically transmissive material (e.g., sapphire, alumina, crown glass, polycarbonate, and other plastics).
Transmissive plate 174 and shaped lens 172 are spaced above the light emitting surface of LEDs 102 by a clearance distance. In some embodiments, separation is desirable to allow clearance for wire bond connections from the LED package submount to the active area of the LED. In some embodiments, a clearance of one millimeter or less is desirable to allow clearance for wire bond connections. In some other embodiments, a clearance of two hundred microns or less is desirable to enhance light extraction from the LEDs 102.
In some other embodiments, the clearance distance may be determined by the size of the LED 102. For example, the size of the LED 102 may be characterized by the length dimension of any side of a single, square shaped active die area. In some other examples, the size of the LED 102 may be characterized by the length dimension of any side of a rectangular shaped active die area. Some LEDs 102 include many active die areas (e.g., LED arrays). In these examples, the size of the LED 102 may be characterized by either the size of any individual die or by the size of the entire array. In some embodiments, the clearance should be less than the size, e.g., the length of a side, of the LED 102. In some embodiments, the clearance should be less than twenty percent of the size of the LED 102. In some embodiments, the clearance should be less than five percent of the size of the LED. As the clearance is reduced, light extraction efficiency may be improved, but output beam uniformity may also degrade.
In some other embodiments, it is desirable to attach transmissive plate 174 or shaped lens 172 directly to the surface of the LED 102. In this manner, the direct thermal contact between transmissive plate 174 or shaped lens 172 and LEDs 102 promotes heat dissipation from LEDs 102. In some other embodiments, the space between mounting board 104 and transmissive plate 174 or shaped lens 172 may be filled with a solid encapsulate material. By way of example, silicone may be used to fill the space. In some other embodiments, the space may be filled with a fluid to promote heat extraction from LEDs 102.
In the embodiment illustrated in
In some embodiments, multiple, stacked transmissive layers are employed. Each transmissive layer includes different wavelength converting materials. For example, as illustrated in
In some embodiments, any of the wavelength converting materials may be applied as a pattern (e.g., stripes, dots, blocks, droplets, etc.). For example, as illustrated in
As illustrated in
As illustrated in
In the illustrated embodiments, wavelength converting materials are located on the surface of transmissive layer 174. However, in some other embodiments, any of the wavelength converting materials may be embedded within transmissive layer 174.
The area between LEDs 102 and transmissive plate 174 or shaped lens 172 may be filled with a non-solid material, such as air or an inert gas, so that the LEDs 102 emits light into the non-solid material. By way of example, the cavity may be hermetically sealed and Argon gas used to fill the cavity. Alternatively, Nitrogen may be used. In other embodiments, the area between LEDs 102 and transmissive plate 174 or shaped lens 172 may be filled with a solid encapsulate material. By way of example, silicone may be used to fill the cavity. In some other embodiments, color conversion cavity 160 may be filled with a fluid to promote heat extraction from LEDs 102. In some embodiments, wavelength converting material may be included in the fluid to achieve color conversion.
In some embodiments, the dam of thermally conductive material 190 is spaced apart from the dam of reflective material 192. The space allows excess optically translucent material 177 to pour over the dam of reflective material 192 when transmissive plate 174 is attached without interfering with the thermal connection between thermally conductive material 190 and transmissive plate 174. In some other embodiments, the dam of reflective material is in contact with the dam of thermally conductive material 190. In one example, the reflective material is a flowable material (e.g., silicone based material) that is dispensed within the dam of thermally conductive material 190. The reflective material wicks up the edge of the dam of thermally conductive material 190 to shield the dam of thermally conductive material from exposure to light emitted from LEDs 102. In some embodiments, the dam of thermally conductive material 190 envelopes the edge of transmissive plate 174, which provides a larger surface area of thermal contact and also allows the effective aperture of the LED based illumination device to be defined by the dam of thermally conductive material 190.
In general, the dam of reflective material 192 is constructed from a highly reflective material. The emphasis is on selection of materials with high reflectivity to minimize optical losses in LED based illumination device 100. The thermal conductivity of the highly reflective material 192 is of secondary importance due to the presence of the dam of thermally conductive material 190. In contrast, the dam of thermally conductive material 190 is constructed from a material with high thermal conductivity. The emphasis is on selection of materials with high thermal conductivity to minimize the thermal resistance between transmissive plate 174 and mounting board 104. The reflectivity of the thermally conductive material 190 is of secondary importance due to the presence of the dam of highly reflective material 192 that is in the optical path of LEDs 102. In this manner, a first dam of material, e.g., dam of highly reflective material 192, surrounds the LEDs 102 with the objective of minimizing optical losses, and a second dam of material, e.g., dam of thermally conductive material 190, surrounds the first dam with the objective of focusing on thermal performance. Importantly, the thermal dam is optically shielded from LEDs 102 by the optical dam; hence, the optical performance of the thermal dam is not critical. Rather than being forced to select a dam material that is neither optically nor thermally optimal, this approach allows the designer to choose separate materials, one optimized for optical performance, and the other optimized for thermal performance for each respective dam of material.
In some embodiments, the dam of reflective material 192 is a highly reflective silicone, and the dam of thermally conductive material 190 is a thermally conductive silicone. However, other materials may be contemplated. For example, as illustrated in
In one example, LED based illumination device 100 is constructed in part by bonding the dam of thermally conductive material 190 to LED mounting board. For example, the dam of thermally conductive material 190 is a metal structure (e.g., nickel plated aluminum, copper, etc.) that is bonded onto LED board 104 (e.g., reflow solder, epoxy, etc.). The LED board 104 is populated with LEDs 102 and electrical connections are made between the LED die and LED board 104. Flowable, reflective material is deposited within the dam of thermally conductive material 190 and in the space between the LEDs 102. The reflective material wicks up the edge of the dam of thermally conductive material 190 to shield the dam of thermally conductive material from exposure to light emitted from LEDs 102. The transmissive plate 174 is bonded to the dam of thermally conductive material 190 (e.g., using glue, epoxy, etc.).
In general, base reflector structure 200 is constructed from a reflective material with high thermal conductivity. In some embodiments, a highly reflective, thermally conductive silicone material is employed. By controlling the spatial distribution of the silicone as it is dispensed on LED mounting board 104, a cup-like shape can be formed around the LEDs 102. In this manner, large angle light emission from the LEDs 102 is directed toward transmissive plate 174 by base reflector structure 200.
In another aspect, transmissive plate 174 is coupled to LED mounting board 104 by a thermally conductive structure and an optically reflective structure to promote heat transfer from transmissive plate 174 to mounting board 104 and to promote light extraction from the LED based illumination device.
Although certain specific embodiments are described above for instructional purposes, the teachings of this patent document have general applicability and are not limited to the specific embodiments described above. For example, although LED based illumination device 100 is depicted as emitting from the top of the device (i.e., the side opposite the LED mounting board 104), in some other embodiments, LED based illumination device 100 may emit light from the side of the device (i.e., a side adjacent to the LED mounting board 104). In another example, any component of LED based illumination device 100 may be patterned with phosphor. Both the pattern itself and the phosphor composition may vary. In one embodiment, the illumination device may include different types of phosphors that are located at different areas of LED based illumination device 100. For example, a red phosphor may be located on the bottom side of transmissive plate 174 and yellow and green phosphors may be located on the top of transmissive plate 174. In one embodiment, different types of phosphors, e.g., red and green, may be located on different areas on transmissive plate 174 or shaped lens 172. For example, one type of phosphor may be patterned on transmissive plate 174 or shaped lens 172 at a first area, e.g., in stripes, spots, or other patterns, while another type of phosphor is located on a different second area of on transmissive plate 174 or shaped lens 172. If desired, additional phosphors may be used and located in different areas. Additionally, if desired, only a single type of wavelength converting material may be used and patterned on transmissive plate 174 or shaped lens 172. In another example, LED based illumination device 100 is depicted in
Claims
1. An LED based illumination device comprising:
- a plurality of LEDs mounted to an LED mounting board;
- a first transmissive plate disposed above the plurality of LEDs, the first transmissive plate includes a first amount of a first wavelength converting material configured to change a wavelength of an amount of light emitted by the plurality of LEDs; and
- a base reflector structure coupled to the LED mounting board between at least two of the plurality of LEDs and extending to the first transmissive plate over a contact area.
2. The LED based illumination device of claim 1, wherein the contact area between the base reflector structure and the first transmissive plate is shaped as a grid pattern between the plurality of LEDs.
3. The LED based illumination device of claim 1, wherein the contact area between the base reflector structure and the first transmissive plate is a matrix of contact points between the plurality of LEDs.
4. The LED based illumination device of claim 1, further comprising:
- a plurality of total internal reflection (TIR) lens elements disposed between each of the plurality of LEDs and the first transmissive plate, wherein each of the TIR lens elements are disposed within the base reflector structure.
5. The LED based illumination device of claim 1, further comprising:
- an encapsulant material disposed between the base reflector structure and the first transmissive plate over the plurality of LEDs.
6. The LED based illumination device of claim 1, further comprising:
- a second transmissive plate disposed above the first transmissive plate, the second transmissive plate includes a second amount of a second wavelength converting material configured to change the wavelength of a second amount of light emitted by the plurality of LEDs.
7. The LED based illumination device of claim 1, wherein the first transmissive plate includes a second amount of a second wavelength converting material configured to change a wavelength of the amount of light emitted by the plurality of LEDs.
8. An LED based illumination device comprising:
- a plurality of LEDs mounted to an LED mounting board;
- a first transmissive plate disposed above the plurality of LEDs, the first transmissive plate includes a first amount of a first wavelength converting material configured to change a wavelength of an amount of light emitted by the plurality of LEDs;
- a dam of reflective material surrounding the plurality of LEDs and coupled to the LED mounting board and the first transmissive plate; and
- a dam of thermally conductive material surrounding the dam of reflective material, wherein the dam of thermally conductive material is coupled to the LED mounting board and the first transmissive plate.
9. The LED based illumination device of claim 8, wherein the dam of thermally conductive material is spaced apart from the dam of reflective material.
10. The LED based illumination device of claim 8, wherein the dam of thermally conductive material is in contact with the dam of reflective material.
11. The LED based illumination device of claim 8, wherein the dam of reflective material optically shields the dam of thermally conductive material from the amount of light emitted by the plurality of LEDs.
12. The LED based illumination device of claim 8, further comprising:
- a plurality of total internal reflection (TIR) lens elements disposed between each of the plurality of LEDs and the first transmissive plate.
13. The LED based illumination device of claim 8, further comprising:
- an encapsulant material disposed between the plurality of LEDs and the first transmissive plate.
14. The LED based illumination device of claim 8, further comprising:
- a second transmissive plate disposed above the first transmissive plate, the second transmissive plate includes a second amount of a second wavelength converting material configured to change a wavelength of the amount of light emitted by the plurality of LEDs.
15. The LED based illumination device of claim 8, wherein the first transmissive plate includes a second amount of a second wavelength converting material configured to change a wavelength of the amount of light emitted by the plurality of LEDs.
16. An LED based illumination device comprising:
- a plurality of LEDs;
- an optically transmissive element disposed above the plurality of LEDs, the optically transmissive element includes a first amount of a first wavelength converting material configured to change a wavelength of an amount of light emitted by the plurality of LEDs; and
- an LED mounting board, the plurality of LEDs mounted on a first side of the LED mounting board, the LED mounting board having a protrusion of thermally conductive material on the first side of the LED mounting board surrounding the plurality of LEDs, wherein the LED mounting board is coupled to the optically transmissive element at the protrusion, and wherein the LED mounting board includes a void on a second side of the LED mounting board opposite the protrusion.
17. The LED based illumination device of claim 16, wherein the protrusion is formed on the first side of the LED mounting board by forming the void on the second side of the LED mounting board.
18. The LED based illumination device of claim 16, wherein the optically transmissive element is a transmissive plate.
19. The LED based illumination device of claim 16, wherein the optically transmissive element is a shaped lens element.
20. The LED based illumination device of claim 16, further comprising:
- an encapsulant material disposed between the plurality of LEDs and the optically transmissive element.
Type: Application
Filed: Sep 3, 2013
Publication Date: Jan 2, 2014
Applicant: Xicato, Inc. (San Jose, CA)
Inventors: Gerard Harbers (Sunnyvale, CA), Tyler Robin Kakuda (Stockton, CA), Serge J. A. Bierhuizen (San Jose, CA), Stefan Eberle (Mountain View, CA)
Application Number: 14/017,201
International Classification: F21K 99/00 (20060101);