A WHITE LIGHT EMITTING DEVICE

Abstract

A white light emitting device with an efficiency of at least 230 lm/W at a blue LED chip input current density from 10 to 60 mA/mm.sup.2, preferably in the range from 15 to 40 mA/mm.sup.2 and more preferably in the range from 20 to 30 mA/mm.sup.2. The device comprises a substrate, at least one string of blue LED chips mounted on the substrate and a phosphor material composition. Said phosphor material composition comprises a narrow band red phosphor which generates light with a peak emission wavelength in a range from 625 nm to 635 nm. The weight percentages of the narrow band red phosphor are between 33 to 49 wt. % for a CCT of from 4000 to 6500K or in an amount of from 60 to 70 wt. % for a CCT of from 2700 to 3500K CCT.

Claims

1. A white light emitting device comprising: a substrate; at least one string of blue LED chips mounted on the substrate, with a dominant wavelength in the range from 445 nm to 460 nm; and a phosphor material composition comprising: a yellow green phosphor material which generates light with a peak emission wavelength in a range 520 nm to 580 nm; and a narrow band red phosphor material which generates light with a peak emission wavelength in a range 625 nm to 635 nm; wherein the phosphor material composition comprises the narrow band red phosphor material in an amount of from 33 to 49 wt. % for a CCT of from 4000 to 6500K or in an amount of from 60 to 70 wt. % for a CCT of from 2700 to 3500K CCT; and wherein the device is adapted to generate a white light output with an efficiency of at least 230 lm/W at a blue LED chip input current density in a range from 10 to 60 mA/mm.sup.2.

2. The device of claim 1, wherein the blue LED chip input current density is in a range of 20 to 30 mA/mm.sup.2.

3. The device of claim 1, wherein phosphor material composition comprises the narrow band red phosphor material in an amount of from 33 to 43 wt. % for a CCT of from 5000K to 6500K.

4. The device of claim 1, wherein the phosphor material composition comprises the yellow green phosphor material in an amount of from 44 to 74 wt. % for a CCT of from 4000 to 6500K or from 22-45 wt. % for a CCT of from 2700 to 3500K.

5. The device of claim 1, wherein the phosphor material composition comprises the yellow green phosphor material in an amount of from 51 to 67 wt. % and the narrow band red phosphor material in an amount of is from 33 to 49 wt. % for a CCT of from 4000 to 6500K.

6. The device of any of claim 1, wherein, for a CCT of between 2700 to 3500K, the phosphor material composition further comprises a broad spectrum red phosphor material; and wherein, for a CCT of between 2700 to 3500K, the phosphor material composition comprises: the broad spectrum red phosphor material in an amount of from 1 to 4 wt. %; the yellow green phosphor material in an amount of from 30 to 35 wt. %; and the narrow band red phosphor material in an amount of from 64 to 67 wt. %.

7. A white light emitting device comprising: a substrate. at least one string of blue LED chips mounted on the substrate, with a dominant wavelength in the range from 445 nm to 460 nm; and a phosphor material composition comprising: a yellow green phosphor material which generates light with a peak emission wavelength in a range 520 nm to 580 nm; and a narrow band red phosphor material which generates light with a peak emission wavelength in a range 625 nm to 635 nm; wherein the device is adapted to generate a white light output with an efficiency of at least 230 lm/W at a blue LED chip input current density in a range from 10 to 60 mA/mm.sup.2, and wherein a color point (x, y) of the white light output with respect to the chromaticity specification for SSL products defined in 7-Step Quadrangles of Annex A in ANSI standard C78.377 is within the range of: $0.3<x<0.5;\mathrm{and}$ $-2.3172x^2+2.3653x-0.170<y<-2.3172x^2+2.3653x-0.146;$ wherein, x and y are chromaticity coordinates according to CIE 1931 color diagram.

8. The device of claim 7, wherein the color point range of the white light output is above the black body locus and at a distance to the black body locus of at least 5 SDCM.

9. The device of claim 7, wherein the device is adapted to generate a white light output with an efficiency of at least 230 lm/W at a blue LED chip input current density in a range from 15 to 40 mA/mm.sup.2.

10. The device of claim 1, wherein the ccy position of the white light output is in a range 0.02-0.03 higher than the blackbody curve.

11. The device of claim 1, wherein the substrate and the string of blue LED chips are arranged as a LED filament.

12. The device of claim 1, wherein the yellow green phosphor material comprises YAG, GaYAG or LuYAG; and wherein the narrow band red phosphor material comprises K.sub.2SiF.sub.6:Mn.sup.4+.

13. The device of claim 1, wherein for a CCT of between 4000K to 6500K, the accumulated spectrum intensity ratio from 480 nm to 600 nm is higher than 50% of the total white spectrum from 380 nm to 780 nm; or wherein for a CCT of between 2700K to 3500K, the accumulated spectrum intensity ratio from 480 nm to 600 nm is higher than 45% of the total white spectrum.

14. The device of claim 1, wherein the blue LED chip size is in the range 0.18 mm.sup.2 to 0.30 mm.sup.2.

15. The device of claim 1, wherein the blue LED chip to chip distance is equal or greater than 0.4 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Embodiments of the invention will now be described with reference to the accompanying figures, in which:

[0057] FIG. 1 shows a schematic view of a white light emitting device according to an embodiment of the invention.

[0058] FIG. 2 shows a schematic view of a white light emitting device according to an embodiment of the invention.

[0059] FIG. 3A shows a substrate and string of blue LEDs as a LED filament in a device and

[0060] FIG. 3B shows the device configured as a LED filament bulb according to an embodiment of the invention.

[0061] FIGS. 4A-B show two and three interdigitating electrode tracks respectively on a substrate of a white light emitting device.

[0062] FIG. 5A shows a graph of efficiency versus current density of a white light emitting device comprising a series of blue LED chips.

[0063] FIG. 5B shows a graph of wall plug efficiency (WPE) of the series of blue LED chips (without phosphor covering over the LED chips) versus current density of the current flowing through these chips.

[0064] FIGS. 6A-C show graphs of relative radiant power versus wavelength for devices comprising a phosphor material composition comprising: in 6A) only a green phosphor; in 6B) a green phosphor and broad spectrum red phosphor; and in 6C) a green phosphor and a narrow band red phosphor.

[0065] FIGS. 7A and 7B show spectral power distribution for two different devices; in 7a) the device has a ccy on the black body locus and in 7b) the device has a ccy of around 0.03 higher than the black body locus according to an embodiment of the invention;

[0066] FIG. 8 shows the human eye sensitive function for different colors;

[0067] FIGS. 9 and 10 show the defined higher y color coordinates coverage above ANSI C78.377 bin range; and

[0068] FIG. 11 shows the parameters of MacAdam ellipse.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0069] In an aspect, there is provided a white light emitting device comprising: a substrate; at least one string of blue LED chips mounted on the substrate, with a dominant wavelength in the range from 445 nm to 460 nm; and a phosphor material composition comprising: a yellow green phosphor material which generates light with a peak emission wavelength in a range 520 nm to 580 nm; and a narrow band red phosphor material which generates light with a peak emission wavelength in a range 625 nm to 635 nm; wherein the phosphor material composition comprises the narrow band red phosphor material in an amount of from 33 to 49 wt. % for a CCT of from 4000 to 6500K or in an amount of from 60 to 70 wt. % for a CCT of from 2700 to 3500K CCT; and wherein the device is adapted to generate a white light output with an efficiency of at least 230 lm/W at a blue LED chip input current density in a range from 10 to 60 mA/mm.sup.2.

[0070] In embodiments, the weight percentages of the phosphor materials in the phosphor material compositions of the devices can vary and depend on the CCT that is desired.

[0071] For narrow band red phosphor, for a CCT of from 4000 to 6500 K, the weight percentage is from 26 to 56 wt. %. For example, the weight percentage can be from 33 to 49 wt. %. The weight percentage can also be from 44 to 54 wt. % in some embodiments. In further embodiments, this can be 49%, for a CCT of 4000K. The weight percentage can also be from 33 to 43 wt. %, and, in further embodiments, 38 wt. %, for a CCT of from 5000 to 6000K. For a CCT of from 2700 to 3500K, the weight percentage of the narrow band red phosphor is from 55 to 74 wt. %. For example, the weight percentage can be from 64 to 66 wt. %. More specifically, the weight percentages of the narrow band red phosphor materials for the corresponding CCTs can be: for 2700K, between 60 to 74 wt. % and, in further embodiments, 67 wt. %; for 3000K, between 55 to 69 wt. % and, in further embodiments, 62 wt. %; for 4000K, between 42 to 56 wt. % and, in further embodiments, 49 wt. %; and for 6500 K, between 26 to 40 wt. % and, in further embodiments, 33 wt. %.

[0072] For the yellow green phosphor material, for a CCT of from 4000K to 6500K, the yellow green phosphor weight material percentage can be from 44 to 74 wt. %. For a CCT of from 2700 to 3500 K, the yellow green phosphor material weight percentage can be from 22 to 45 wt. %.

[0073] Examples of the weight percentages in embodiments of the invention can therefore be, for a CCT of 4000K, 49 wt. % narrow band red phosphor and 51 wt. % yellow green phosphor and, for a CCT of 6500K, 33 wt. % narrow band red phosphor and 67 wt. % yellow green phosphor.

[0074] The weight percentage of the broad spectrum red phosphor material may be from 1 to 4 wt. %. For example the weight percentage may be 3 wt. %. An example of a device in accordance with an embodiment of the invention comprising a broad red phosphor for a CCT of 2700K can therefore comprise: a narrow band red phosphor at 67 wt. %; a yellow green phosphor at 30 wt. % and a broad spectrum red phosphor at 3 wt. %. An example of another device in accordance with an embodiment of the invention comprising a broad red phosphor for a CCT of 3000K can comprise: a narrow band red phosphor at 62 wt. %; a yellow green phosphor at 35 wt. % and a broad spectrum red phosphor at 3 wt. %.

[0075] Embodiments for which the device comprises a LED filament can comprise a single or multiple LED filaments arranged in multiple ways. For example, a single or multiple LED filament(s) could be arranged in various shapes such as spiral(s), coil(s), ring(s), or rod(s) inside a bulb or any alternative housing shape such as a cube, cylinder or ellipsoid. The LED filament can comprise multiple types of substrate such as glass or ceramic or sapphire. Particularly, sapphire substrates in LED filaments can provide an additional 1-2% efficiency gain owing to their increased transparency (compared to glass or ceramic substrates) which contributes to more backside white light output.

[0076] Embodiments which comprise either a two or three-finger layout can be arranged in a variety of ways and the device can comprise single two or three-finger layouts or multiple two or three-finger-layouts.

[0077] The size of the blue LED chip in embodiments of the invention can also vary. In some cases the size is between 0.18-0.30 mm.sup.2. In some embodiments the size of the chip is 0.2 mm.sup.2.

[0078] The invention will be described with reference to the Figures. A first embodiment of the invention is shown in FIG. 1. A white light emitting device 1 comprises blue LED chips 2 mounted on a substrate 3. A phosphor material composition comprising a yellow green phosphor material 4 and a narrow band red phosphor material 5 is deposited over blue LED chips 2. The blue LED chips 2 and phosphor material composition of this device are sealed inside the device by an encapsulant 7. Wiring 6 is provided to connect blue LEDs 2.

[0079] In one specific implementation of the embodiment of FIG. 1, the device has a CCT of 4000K and the phosphor material composition comprises 49 wt. % narrow band red phosphor 5 and 51 wt. % yellow green phosphor 4.

[0080] A further embodiment of the invention is shown in FIG. 2. A white light emitting device 101 comprises blue LED chips 102 mounted on a substrate 103. A phosphor material composition comprising: a yellow green phosphor material 104; a narrow band red phosphor material 105; and a broad spectrum red phosphor material 108 is deposited over blue LED chips 102. The blue LED chips 102 and phosphor material composition of this device are sealed inside the device by an encapsulant 107. Wiring 106 is provided to connect blue LEDs 102.

[0081] In one specific implementation of the embodiment of FIG. 2, the device has a CCT of 2700K and the phosphor material composition of this embodiment comprises: a narrow band red phosphor at 67 wt. %; a yellow green phosphor at 30 wt. % and a broad spectrum red phosphor at 3 wt. %.

[0082] FIG. 3A shows a LED filament 200 of a white light emitting device. The LED filament 200 comprises a substrate 203 and a string of blue LED chips 202. The string of blue LED chips 202 are mounted onto substrate 203. Each blue LED chip 202 has a size of 0.18 mm.sup.2 to 0.30 mm.sup.2 and is separated from the adjacent blue LED chip 202 by a distance d of at least 0.4 mm.

[0083] FIG. 3B shows a further embodiment of the invention in which a white light emitting device 204 comprises four of the LED filaments 200 of FIG. 3A. In alternative embodiments a different number of LED filaments may be used. Although not depicted, the device 204 further comprises a phosphor material composition comprising a yellow green phosphor material and a narrow band red phosphor material is deposited over blue LED chips 016. As shown in FIG. 3b shows the multiple LED filaments 200 arranged in a bulb-shaped housing to mimic a traditional incandescent light bulb appearance. Substrate 203 is a sapphire substrate.

[0084] Alternatively, in a different embodiment, the device 3 of FIGS. 3A and 3B comprises an alternative phosphor material composition comprising: a yellow green phosphor material; a narrow band red phosphor material; and a broad spectrum red phosphor material, that is deposited over blue LED chips. The device has a CCT of 2700K, the phosphor material composition of this embodiment comprises: a narrow band red phosphor at 67 wt. %; a yellow green phosphor at 30 wt. % and a broad spectrum red phosphor at 3 wt. %.

[0085] FIG. 4A shows two electrodes arranged as two interdigitating elongate tracks 310 on a substrate 302 of a white light emitting device 300. This arrangement of the electrode tracks is termed a two-finger layout. Two soldering pads 311 are arranged on the substrate 302 and connect to the interdigitating electrode tracks 310. Alternatively, FIG. 4B shows three electrodes arranged as three interdigitating elongate tracks 410 on a substrate 402 of a white light emitting device 400. This arrangement is termed a three-finger layout. Two soldering pads 411 are arranged on the substrate 402 and connect to the interdigitating electrode tracks 410. In embodiments, white light emitting devices can comprise the two or three-finger layouts 300 and 400 of FIGS. 4A and 4B. Such devices 300 and 400 can further comprise blue LED chips mounted on a substrate. Phosphor material compositions comprising a yellow green phosphor material and a narrow band red phosphor material are deposited over blue LED chips. The devices have a CCT of 4000K, the phosphor material compositions of these embodiments comprise 49 wt. % narrow band red phosphor and 51 wt. % yellow green phosphor.

[0086] FIG. 5A shows an efficiency curve at applied current densities of a white light emitting device comprising a series of blue LED chips. It has been found through experimentation that the range of the applied current densities that gives the optimum efficiency of devices according to embodiments of this invention is between 10-60 mA/mm.sup.2 and preferably 20-30 mA/mm.sup.2 and in some embodiments it is 25 mA/mm.sup.2. After this range, the efficiency of the device falls off. Where used with the specific phosphor material composition and/or the other efficiency improvements disclosed herein, it has been found that this can be unexpectedly be further improved at this current density to provide an increased lm/W output. FIG. 5B shows the wall plug efficiency (WPE) curve of the series of blue LED chips, without phosphor covering over the LED chips, at applied current density. It can be seen that, comparing with the curve in FIG. 5A, when the current density increases over the peak, the WPE (of blue LED chips) decreases much slower than efficiency (of white light emitting device) does, for example, in FIG. 5A, both around 10 and 60 mA/mm.sup.2 reach 230 lm/W, but in FIG. 5B, the WPE of 60 mA/mm.sup.2 is higher than that of 10 mA/mm.sup.2, at a gap G. The reason of such a quick decrease of efficiency with respect to current density in the white light emitting device is the thermal sensitivity of narrow band red phosphor material, e.g., KSF phosphor. The combination of the phosphor composition and the setting of the specific current density according to the present disclosure to gather contribution to the increased lm/W output as high as 230 lm/W.

[0087] FIG. 6A shows a spectral power distribution for a device, not in accordance with the invention, comprising a yellow green phosphor material only in the phosphor material composition. Using only a yellow green phosphor material can achieve relatively high efficiency, but this is to the detriment of the color-rendering index. FIG. 6B shows a spectral power distribution for a device comprising a phosphor material composition comprising both a green and broad red phosphor materials, not in accordance with the invention. The color-rendering index properties are improved compared to the distribution for the device shown in FIG. 6A. FIG. 6C shows a spectral power distribution for a device with a green phosphor and a narrow band red phosphor in the phosphor material composition in accordance with the invention. In this embodiment, the color-rendering index properties of the device are much improved and the radiant powder of the red is seen to be much higher than for the other two devices.

[0088] Radiant power is measured in Watts and is defined as the amount of light emitted from a source irrelevant of the direction it is emitted at each wavelength. In embodiments, radiant power measurement is carried out using of a spectrophoto- or spectroradiometer connected to an integrating sphere.

[0089] FIG. 7A shows a spectral power distribution for a device not in accordance with an embodiment of the invention for a CCT of 4000K. FIG. 7B shows a spectral power distribution for a device in accordance with an embodiment of the invention. This device is seen to have much higher efficiency owing to the incorporation of the narrow band red phosphor in the specified phosphor weight percentage range at the CCT of 4000K.

Examples of Phosphor Material Compositions within Devices

[0090] The following are examples of devices in accordance with embodiments of the invention, with the current density and resulting efficiency as shown in FIG. 5A.

TABLE-US-00002 TABLE 1 CCT Yellow green Broad spectrum red Narrow band red No. (K) phosphor (wt. %) phosphor (wt. %) phosphor (wt. %) 1 2700 30 3 67 2 3000 35 3 62 3 4000 51 0 49 4 6500 67 0 33

[0091] These examples comprise the preferred amounts of narrow band red phosphor material in the device for a given CCT. The resulting ratios of the narrow band red phosphor to the yellow green phosphor within the phosphor material composition have been found to exhibit the highest device efficiency at low blue LED chip input current densities in the specified range. This contributes to the overall device efficiency owing to the increase in the phosphor conversion efficiency as described with reference to equation (1).

[0092] By incorporating other above-mentioned features into the device, such as a LED filament, blue LED chip spacing of greater than 0.4 mm and a two-finger layout (in addition to the preferred narrow band red phosphor material weigh percentages in Table 1), the efficiency of the device can be further improved above 230 lm/W. This is due to the corresponding increases in wall plug efficiency and package efficiency as discussed with reference to equation (1).

[0093] Accordingly, it has been found that a device comprising: a chip size of 0.2 mm.sup.2; a two-finger layout; a chip spacing of greater than 0.5 mm and an input current density of the blue LED chip at 0.025 A/mm.sup.2 can have the highest maximum white LED efficiency point with the specified weight percentages given in Table 1.

[0094] These examples comprise the preferred amounts of narrow band red phosphor material in the device for a given CCT. The resulting ratios of the narrow band red phosphor to the yellow green phosphor within the phosphor material composition have been found to exhibit the highest device efficiency at low blue LED chip input current densities in the specified range. This contributes to the overall device efficiency owing to the increase in the phosphor conversion efficiency as described with reference to equation (1).

[0095] By incorporating other above-mentioned features into the device, such as a LED filament, blue LED chip spacing of greater than 0.4 mm and a two-finger layout (in addition to the preferred narrow band red phosphor material weigh percentages in Table 1), the efficiency of the device can be further improved above 230 lm/W. This is due to the corresponding increases in wall plug efficiency and package efficiency as discussed with reference to equation (1).

[0096] FIG. 8 shows the human eye sensitive function for different color. The green spectrum has highest weight percentage than red or blue colors.

[0097] FIGS. 9 and 10 show the defined higher y color coordinates coverage above ANSI C78.377 bin range to get higher efficiency in white color. The bin range refers to the chromaticity specification for SSL products defined in Annex A of ANSI C78.377, 7-Step Quadrangles. In FIG. 9 the CIE 1931 diagram shows the upper and lower limited color range that have higher ccy coordinate than ANSI C78.377 bin range. In FIG. 10, the CIE 1931 diagram shows examples of MacAdam ellipse ranges according to ANSI standard C78.376 that have higher ccy coordinate than ANSI C78.377 bin range.

[0098] FIG. 11 shows the parameters a/b/ of a Macadam ellipse.

[0099] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality.

[0100] The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0101] If the term adapted to is used in the claims or description, it is noted the term adapted to is intended to be equivalent to the term configured to.

[0102] Any reference signs in the claims should not be construed as limiting the scope.