HK1079839A - A method and apparatus for producing untainted white light using off-white light emitting diodes - Google Patents

Description

Method and apparatus for producing white light without stray color using near white light emitting diode

Technical Field

The present invention relates to a method and apparatus for producing unpigmented white light using off-white Light Emitting Diodes (LEDs). More particularly, the present invention relates to a method of combining different hues (hue) of white light from complementary LEDs to produce a more "pure" white light.

Background

A white LED couples two luminescent materials. The first is a blue light emitting diode made of a semiconductor material capable of emitting radiation (i.e., "primary radiation") when an electric current flows through it. The second is a yellow fluorescent or luminescent wavelength converting material that absorbs a portion of the primary radiation and emits light of a different wavelength than the primary radiation (i.e., "secondary radiation"). The combined light is a combination of the secondary radiation and the unconverted part of the primary radiation. In a white LED, the diode emits blue light of the primary radiation and the wavelength converting material emits yellow light of the secondary radiation.

In white LEDs, one desirable resultant radiation is white light without mottling. There are many different types of white light, such as bluish white, also known as cool white, and yellowish white, also known as warm white. Where an equivalent to daylight is required, such as a flash for an image capture device, it is desirable to obtain "pure" white light, i.e., white light without mottle. "pure" white light has been quantified. Fig. 1 is a chromaticity diagram of 1931 CIE (Commission International d' Elchairge, International association for illumination). The dashed line 110 represents the bold curve. The color of radiation from a black body depends only on its temperature. In the lighting industry, white is often specified with a color temperature associated therewith. Point 100 is "pure" white light with no mottle and the color temperature associated with it is 6500 Kelvin. Incidentally, the white light of the point 100 is also a reference white of a National television system Committee (National television system Committee). The dots 100 are the desired hue for a white light emitting device such as an image capture device.

Most white LEDs employ a common yellow phosphor, such as cerium doped yttrium aluminum garnet (YAG: Ce), as the wavelength converting material. In order to obtain white light without mottling with such fluorescent agents, the initial radiation of the blue color typically has a wavelength falling between 465 and 470 nanometers. If the initially radiated blue light is too greenish (i.e., greater than 470 nanometers), the resultant white light will be slightly greenish. If the initially radiated blue light is too violet (i.e., less than 465 nanometers), the resultant white light will be purplish. Both of these mottled white shades are perceptible to the human eye and are referred to as "impure" whites. These mottled shades have color coordinates located away from the black body curve in fig. 1. If any of these impure white lights are used in the flash of an image capture device, the resulting image will also be mottled.

Despite the controlled process, the color of blue light emitted by blue semiconductor materials produced by epitaxial semiconductor growth processes typically varies in the range of 460 to 480 nanometers. Thus, only about 25% of the available blue semiconductor material produced by this process can be used in the diodes of "pure" white LEDs. The remaining 75% of the emitted blue light is either too green or too violet to be used for this purpose. The production costs of "pure" white LEDs are therefore very high.

Accordingly, there is a need in the industry for a method or apparatus that produces non-mottled white light from LEDs in a more economically feasible manner. The present invention addresses this problem by providing a unique and novel solution.

Disclosure of Invention

A white light emitting device using a near-white Light Emitting Diode (LED) is disclosed. The white light emitting device is not limited to using only pure white LEDs, but rather arranges the LEDs that appear near white in a manner such that the combination of light emitted from the near white LEDs produces radiation that appears substantially pure white to the human eye.

Drawings

The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:

fig. 1 is a representation of a 1931 CIE (international association for lighting) chromaticity diagram.

FIG. 2A shows a flow chart of a process for dividing blue diodes, assembling white LEDs with them, and arranging the LEDs such that their composite light is "pure" white light;

FIG. 2B shows a flow chart of a process for dividing near-white LEDs and arranging the LEDs so that their composite light is "pure" white light;

FIG. 3A is a top view of a 1 × 3 array of white LEDs on a substrate (substrate);

FIG. 3B is a side view of a 1 × 3 array of white LEDs on a substrate;

FIG. 4A is a top view of a 2 × 2 array of white LEDs on a substrate;

FIG. 4B is a side view of a 2 × 2 array of white LEDs on a substrate;

FIG. 5A is a top view of an array of white LEDs in a cavity (cavity) on a substrate;

FIG. 5B is a side view of the white LED array in a cavity on the substrate;

FIG. 6 is a representation of an image capture device, an exemplary embodiment of the present invention. In this case, the image capturing device is a cellular phone having a camera thereon, and the flash for the image capturing device is a 1 × 3 LED as shown in fig. 3A and 3B.

Detailed Description

The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:

the result of combining the primary and secondary radiation in the LED can be shown on the chromaticity diagram (fig. 1). A line segment is drawn between coordinate points representing the color of the primary radiation and the color of the secondary radiation, in this case the colors of the primary radiation and the secondary radiation are blue and yellow, respectively. The resultant light has a color coordinate point located on the line segment. Point "B" is blue light. Point "Y" is yellow light. The color coordinate point of "pure" white light lies on line segment B-Y, in the vicinity of the black body curve. Point "GB" is greenish blue light. The point "GW", or greenish white light, lies on the line segment GB-Y. The point "PB" is violet blue light. The point "PW", or more violet white light, lies on the line segment PB-Y.

In one embodiment of the invention, the LEDs are selected such that one LED having color coordinates on one side of the black body curve is arranged in close proximity to another LED having color coordinates on the other side of the black body curve. The resulting color lies on the locus of a straight line connecting the two color coordinates and is therefore closer to the blackbody curve. The greenish white LEDs and the purplish white LEDs may be suitably arranged to produce radiation that appears to the eye to be substantially white.

In one embodiment of the invention, a greenish white LED is fabricated using a blue diode having a color of 480 nanometers, and a purplish white LED is fabricated using a blue diode having a color of 460 nanometers. In another embodiment, a greenish white LED is fabricated using a blue diode having a color of 475 nanometers, and a purplish white LED is fabricated using a blue diode having a color of 465 nanometers.

As such, a range of blue diodes greater than 5 nanometers may be used. Therefore, the utilization rate of the blue diode is improved, and the production cost is reduced.

Referring to fig. 1, the color coordinates of a combination of any two points on the chromaticity diagram are located on a line segment connecting the two points. Thus, point 100 is located in the vicinity of the blackbody curve on line segment GW-PW and is substantially "pure" white light. By suitably selecting the ratio between greenish white light and purplish white light, white light is generated at the point 100, close to or on the blackbody curve.

Fig. 2A shows a system for sorting blue diodes according to their emitted light wavelength. The white LED is assembled using divided blue diodes. The LEDs are then arranged on the device such that their combined light is white light without mottling. Thus, a white LED can be manufactured using 100% of the blue semiconductor material produced by the conventional process. The blue diodes are divided into three groups depending on the wavelength of blue light of each blue diode: PB, B and GB. Group PB consists of violet-biased blue diodes emitting light with a wavelength in the range of 460 to 465 nanometers. Group B consists of blue diodes emitting light with a wavelength in the range of 465 to 470 nanometers. Group GB consists of greenish blue diodes emitting light with a wavelength in the range 470 to 480 nanometers.

Fig. 2B shows another system that classifies near-white and white LEDs for creating "pure" white light. In this way, a white LED can be manufactured using 100% of the blue semiconductor material produced by conventional processes. Depending on the color coordinates of the white combined light of each LED, the white LEDs are divided into three groups: PW, W, and GW. Group PW consists of violet-biased white LEDs fabricated with diodes emitting light with wavelengths in the range of 460 to 465 nanometers. Group W consists of "pure" white LEDs, which are fabricated with diodes emitting light at wavelengths in the range 465 to 470 nanometers. Group GW consists of greenish white LEDs fabricated with diodes emitting light with wavelengths in the range of 470 to 480 nanometers.

Fig. 3A and 3B show possible arrangements of three white LEDs, one selected from each group. The array 300 is a 1 x 3 matrix. In a preferred embodiment, LED 310 is from group GW, LED320 is from group PW, and LED 330 is from group W (see FIG. 2B). The combination of the light of the three LEDs is pure white light, as shown on the chromaticity diagram. Experiments have shown that the actual arrangement of the LEDs 310, 320 and 330 is not important, and that the combined light of any arrangement is pure white.

In fig. 3A and 3B, the diode is coupled with a substrate 302 having conductive traces (not shown). A bond wire 304 is made from one end of the LED terminals to the conductive traces on the substrate. A layer of a mixture 306 of encapsulant and phosphor is coated over the diode.

Fig. 4A and 4B show an array 400 of four white LEDs arranged in a 2 x 2 matrix. In the preferred embodiment, LEDs 410 and 420 are from group GW and LEDs 430 and 44 are from group PW (see FIG. 2B). In a preferred embodiment, as shown in fig. 4A and 4B, LEDs 410 and 430 are arranged in a first row, while LEDs 420 and 440 are arranged in a second row. Experiments have shown that the actual arrangement of the LEDs 410, 420, 430 and 440 is not important, and the combined light of any arrangement of these four LEDs is pure white light.

In fig. 4A and 4B, the diodes of the LEDs are coupled with a substrate 402 having conductive traces (not shown). Wiring 404 is made from one end of the LED terminals to conductive traces on the substrate. A layer of a mixture 406 of encapsulant and phosphor is coated over the diode.

Fig. 5A and 5B show another preferred embodiment in which the diode is placed in a cavity in the substrate. These cavities act as reflectors, concentrating the light and directing it in the desired direction. The cavity also acts as a container so that it can be first filled with the encapsulant/phosphor mixture and the diode sandwiched between the mixture and the lens containing only the encapsulant. A secondary optical lens placed over the diode is advantageous to further control and enhance the radiation pattern of the light. In a preferred embodiment, a fresnel lens is used.

Preferably, the encapsulant is an epoxy material, but polymers such as thermoplastics and thermosets are also generally suitable. Silicone or glass may also be used. Preferably, the sealant is produced by injection or transfer molding (transfer molding). Casting (casting) processes may also be used. Alternatively, the encapsulant may be a cap (cap) placed over the diode.

In fig. 5A and 5B, the diode is coupled with a substrate 502 having conductive traces (not shown). The substrate has a cavity 501 that acts as a reflector. Wiring 504 is made from one end of the LED terminals to conductive traces on the substrate. A layer of encapsulant/phosphor mixture is coated over the diode and at least partially fills the cavity. A second layer in the shape of a lens containing only encapsulant 506 at least partially covers each diode. Alternatively, encapsulant 506 comprises an encapsulant/phosphor mixture. An auxiliary lens 508 is fitted to the lens side of the LED array.

The arrangement of the LEDs is not limited to a 1 × 3 or 2 × 2 matrix. Any m n array may be used as long as the LEDs from group PW are supplemented by LEDs from group GW, and vice versa (see fig. 2B). The minimum is two LEDs arranged in a 1 x 2 matrix. The LEDs from group W do not need complementary LEDs, since they themselves produce pure white light. In addition, the present invention is not limited to an ordered array of rows and columns, but is equally effective in any systematic two-or three-dimensional class of LED arrays.

The complementary white LEDs may be arranged on a substrate such as a lead frame (leadframe), a printed circuit board, a flexible substrate, glass or ceramic. Alternatively, a plurality of complementary white LED device components such as a via-type or chip LED (chip LED) lamp and a surface mount type PLCC may be arranged on another substrate such as a printed circuit board to generate pure white light. These components are typically placed on the substrate using automated pick and place equipment and then soldered in place using heat exposure.

FIG. 6 is a representation of an image capture device, an exemplary embodiment of the present invention. The image capturing device shown here is a cellular telephone with a camera on it. A 1 x 3 array 601 (see fig. 3A and 3B) provides a flash so that photographs can be taken in cloudy, dark, or night conditions as well.

Claims (27)

1. A light generating device, comprising:

a first light emitting diode that emits light in a first frequency band;

a second light emitting diode that emits light in a second frequency band, wherein a combination of light emitted from the first light emitting diode and the second light emitting diode appears substantially white to a human eye.

2. The apparatus of claim 1, wherein the first light emitting diode emits a purplish-white light corresponding to the first frequency band and the second light emitting diode emits a greenish-white light corresponding to the second frequency band.

3. The apparatus of claim 1, wherein the first light emitting diode has color coordinates on one side of a black body curve and the second light emitting diode has color coordinates on the other side of the black body curve.

4. The device of claim 1, wherein the combination of light from the first light emitting diode emitting the purplish white light and light from the second light emitting diode emitting the greenish white light produces pure white light.

5. The device of claim 1, wherein the first light emitting diode comprises a blue light emitting diode covered by an encapsulant containing a yellow phosphor wavelength converting material.

6. The device of claim 1, wherein the second light emitting diode is covered by an encapsulant containing the yellow phosphor wavelength converting material.

7. The device of claim 2, wherein the first light emitting diode comprises a wavelength of violet-biased blue light between 460 and 465 nanometers.

8. The device of claim 2, wherein the second light emitting diode comprises a greenish blue light wavelength between 470 and 480 nanometers.

9. The apparatus of claim 1, further comprising a plurality of violet-white light emitting diodes and an equal number of green-white light emitting diodes arranged in a complementary manner to the plurality of violet-white light emitting diodes to produce the pure white light.

10. The apparatus of claim 1, wherein light generated by the first and second light emitting diodes is used to illuminate an object for an image capture device.

11. A light emitting device comprising:

an array of arranged light emitting diodes, wherein a light emitting diode having a color coordinate on one side of a black body curve is positioned adjacent to a light emitting diode having a color coordinate on the other side of the black body curve, and wherein the resulting color is located on the locus of a straight line connecting the two color coordinates.

12. The light emitting apparatus of claim 11, wherein the color coordinates comply with colorimetry standards defined by the international association for lighting.

13. The light emitting apparatus of claim 11, wherein the light generated by the light emitting diode is complementary radiation.

14. The light emitting apparatus of claim 11 wherein white light emitting diodes having greenish white and purplish white are arranged in the array to produce radiation that appears substantially white to a human eye.

15. The light emitting apparatus of claim 14 wherein the white light has a color temperature of about one of 6500 kelvin or 9300 kelvin.

16. The light emitting apparatus of claim 11 wherein the greenish white light emitting diode comprises a blue light emitting diode having a 480 nanometer color and the purplish white light emitting diode comprises a blue light emitting diode having a 460 nanometer color.

17. The light emitting apparatus of claim 16 wherein the greenish white light emitting diodes comprise blue light emitting diodes having a color greater than 470 nanometers and the purplish white light emitting diodes comprise blue light emitting diodes having a color less than 465 nanometers.

18. The light emitting apparatus of claim 11 wherein the array comprises a 1 x 3 matrix of light emitting diodes having three light emitting diodes, a first light emitting diode having a color coordinate located on an upper side of the black body curve, a second light emitting diode having a color coordinate located near the black body curve, and a third light emitting diode having a color coordinate located on a lower side of the black body curve.

19. The light emitting apparatus of claim 11 wherein the array comprises at least a 1 x 2 matrix of light emitting diodes having a first light emitting diode having a color coordinate located on an upper side of a black body curve and a second light emitting diode having a color coordinate located on a lower side of the black body curve.

20. The light emitting apparatus of claim 11 wherein the array comprises an LED apparatus assembly.

21. The light emitting apparatus of claim 11 wherein the array comprises a 2 x 2 matrix of light emitting diodes having four light emitting diodes:

a first light emitting diode at an upper left corner having a color coordinate located at an upper side of the black body curve;

a second light emitting diode having a color coordinate located at the upper side of the black body curve at a lower right corner;

a third light emitting diode having a color coordinate located at a lower side of the black body curve at an upper right corner;

a fourth light emitting diode having a color coordinate located on the lower side of the black body curve in the lower left corner.

22. A light emitting device comprising an array of white light emitting diodes having color coordinates that are distant from a black body curve, wherein the combined light has color coordinates that are closer to the black body curve.

23. A white light emitting device comprising:

a substrate having conductive traces;

an array comprising at least one green-blue LED and one violet-blue LED for each green-blue LED, wherein the green-blue LED and the violet-blue LED are attached to the substrate;

an encapsulant covering each LED, the encapsulant containing a yellow phosphor wavelength converting material;

a circuit for providing current to each LED.

24. The white light emitting device of claim 23, wherein there is a cavity on the substrate on which the green-blue LED and the violet-blue LED are disposed, the cavity acting as a reflector in the collection of light and directing the light out in a desired direction.

25. The white light emitting device of claim 23, wherein the encapsulant and the yellow phosphor wavelength converting material are molded into a lens structure to provide a desired radiation pattern of emitted light.

26. The white light emitting device of claim 23, further comprising an optical lens disposed over the LED array to enhance the radiation pattern of the emitted light.

27. The white light emitting device of claim 23, wherein light produced by the green-blue LED and the violet-blue LED is used to illuminate an object for an image capture device.