Multi-color phosphor converted LED package with single cavity

A lighting device includes a first LED configured to emit a first light, a second LED configured to emit a third light, a first phosphor disposed over the first LED and second LED, and arranged to absorb a portion of the first light and in response emit a second light of a longer wavelength than the first light, and a second phosphor disposed over the second LED, the second phosphor arranged to absorb a portion of the third light and in response emit a fourth light of a longer wavelength than the third light, and the fourth light exits the second phosphor into the first phosphor, and both the second light and fourth light exit the lighting device though the first phosphor.

FIELD OF THE INVENTION

This disclosure generally relates to lighting devices using combinations of phosphors and light emitting diodes to create a uniform source appearance.

BACKGROUND

Semiconductor light emitting diodes and laser diodes (collectively referred to herein as “LEDs”) are among the most efficient light sources currently available. The emission spectrum of an LED typically exhibits a single narrow peak at a wavelength determined by the structure of the device and by the composition of the semiconductor materials from which it is constructed. By suitable choice of device structure and material system, LEDs may be designed to operate at ultraviolet, visible, or infrared wavelengths.

LEDs may be combined with one or more wavelength converting materials (generally referred to herein as “phosphors”) that absorb light emitted by the LED and in response emit light of a longer wavelength. For such phosphor-converted LEDs (“pcLEDs”), the fraction of the light emitted by the LED that is absorbed by the phosphors depends on the amount of phosphor material in the optical path of the light emitted by the LED, for example on the concentration of phosphor material in a phosphor layer disposed on or around the LED and the thickness of the layer. Phosphors may be embedded in a silicone matrix that is disposed in the path of light emitted by the LED.

Phosphor-converted LEDs may be designed so that all of the light emitted by the LED is absorbed by one or more phosphors, in which case the emission from the pcLED is entirely from the phosphors. In such cases the phosphor may be selected, for example, to emit light in a narrow spectral region that is not efficiently generated directly by an LED. Alternatively, pcLEDs may be designed so that only a portion of the light emitted by the LED is absorbed by the phosphors, in which case the emission from the pcLED is a mixture of light emitted by the LED and light emitted by the phosphors. By suitable choice of LED, phosphors, and phosphor composition, such a pcLED may be designed to emit, for example, white light having a desired color temperature and desired color-rendering properties

A color point is a point in a chromaticity diagram characterizing a particular spectrum of light as a color perceived by a human with normal color vision. A correlated color temperature (“CCT”) is the temperature corresponding to the point on the blackbody curve in a chromaticity diagram to which a color point is most closely correlated.

SUMMARY

In one aspect a lighting device is disclosed, the lighting device including a first LED configured to emit a first light, a second LED configured to emit a third light, a first phosphor disposed over the first LED and second LED, and arranged to absorb a portion of the first light and in response emit a second light of a longer wavelength than the first light, and a second phosphor disposed over the second LED, the second phosphor arranged to absorb a portion of the third light and in response emit a fourth light of a longer wavelength than the third light, and the fourth light exits the second phosphor into the first phosphor, and both the second light and fourth light exit the lighting device though the first phosphor.

The first phosphor may include a light emitting surface opposite the second LED, the first phosphor, and the first LED, and the second light, fourth light, an unconverted portion of the first light, and an unconverted portion of the third light may pass through the light emitting surface.

The portion of third light absorbed by the second phosphor may be greater than the portion of first light absorbed by the first phosphor.

The first light may have a first wavelength range, a first spectral power distribution of the second light and unconverted first light may have at least 25% of total radiant power within the first wavelength range, and a second spectral power distribution of the fourth light and unconverted third light may have less than 3% of total radiant power in the first wavelength range.

The lighting device may further include a third LED configured to emit a fifth light, and a third phosphor disposed over the third LED and arranged to absorb the fifth light and emit a sixth light, where the sixth light exits the third phosphor into the first phosphor and exits the lighting device through the first phosphor.

The first light, the second light, and the fifth light may each be blue light having a wavelength range of 400-460 nm, the second phosphor may be a red phosphor, and the third phosphor may be a green phosphor.

The first LED, second LED, and third LED may all be mounted within a single lead frame on a mounting surface, the first phosphor comprising a light emitting surface opposite the mounting surface.

Substantially all of the light emitted by the first LED and the second LED that exits the lighting device may pass through the first phosphor.

In another aspect, a lighting device includes a first LED, a second LED, a first phosphor disposed over the first LED and second LED; and a second phosphor disposed over the second LED, between the second LED and the first phosphor, and between the second LED and the first LED.

The first phosphor may include a light emitting surface opposite the second LED, the first phosphor, and the first LED.

The first phosphor may be in direct contact with the first LED and the second phosphor.

The first phosphor may include a light emitting surface, a first light emitted by the first LED enters the first phosphor from the first LED and exits the first phosphor from the light emitting surface, and a second light emitted by the second LED enters the second phosphor from the second LED, exits the second phosphor into the first phosphor, and exits the first phosphor through the light emitting surface.

The first phosphor may include a first phosphor material mixed into a first carrier material and the second phosphor may include a second phosphor material mixed into a second carrier material, and a concentration of second phosphor in second carrier material is higher than a concentration of first phosphor in first carrier material.

The first and second carrier materials may be silicone.

The first LED and second LED may both be mounted within a single lead frame on a mounting surface, the first phosphor having a light emitting surface opposite the mounting surface.

The mounting surface may include a barrier surrounding the second LED and the second phosphor is contained within the barrier.

The lighting device may further include a third LED and a third phosphor, the third phosphor disposed over the third LED, between the first phosphor and the third LED, and between the third LED and the first LED, the first phosphor disposed between the second phosphor and the third phosphor.

The first LED, second LED, and third LED may be semiconductor diode structures configured to emit blue light having a wavelength in the range of 400-460 nm, the second phosphor may be configured to absorbs blue light and emit green light, and the third phosphor may be configured to absorb blue light and emit red light.

The first LED, second LED, and third LED may all be mounted within a single lead frame on a mounting surface, the first phosphor may include a light emitting surface opposite the mounting surface.

The first LED may include a first plurality of semiconductor diode structures and the second LED comprises a second plurality of semiconductor diode structures.

DETAILED DESCRIPTION

The following detailed description should be read with reference to the drawings, in which identical reference numbers refer to like elements throughout the different figures. The drawings, which are not necessarily to scale, depict selective embodiments and are not intended to limit the scope of the invention. The detailed description illustrates by way of example, not by way of limitation, the principles of the invention.

A particular color or white light CCT value of light from a single lighting device can be achieved by means of mixing two or more different colors of light that are emitted from two or more differently colored light sources. Using two or more differently colored light sources (which may be referred to as “primaries”) in a lighting device is particularly useful for a tunable lighting device. In such tunable lighting devices, the color or white light CCT value of the emitted light can be adjusted by varying the amount of light output by the differently colored light sources, or primaries, to achieve varying colors or white light CCT values of the overall emitted light from the lighting device. For instance, color tuning with desaturated red, green, and blue pcLED primaries (as used, for example, in Lumileds Holdings B.V.'s LUXEON Fusion® lighting devices) is an effective approach to achieving high efficacy and flux of white light over a wide CCT range while also providing high color fidelity.

The light sources, or primaries, used in such color tunable and white light CCT tunable lighting devices are typically implemented as discrete LED packages. Thus, two or more discrete LED packages, each emitting a different color of light, are combined to form the tunable lighting device. For example, a white light CCT tunable lighting device may include two discrete LED packages, which may be standard white LED packages, one having a CCT value of 2700K and the other having a CCT value of 6500K.

Combining discrete LED packages can, however, cause a large degree of color variation on the total light emitting surface (“LES”) of the lighting device. This large degree of color variation can be a disadvantage in various optical designs. In directional lighting, color variation of the LES may be visible in the far field, and use of specifically designed secondary optics are required to provide color mixing and reduce color variation. The use of such secondary optics can cause optical efficiency losses and/or an increase in size and volume of the lighting device. In non-directional lighting, it is often desirable for the lighting device to have a uniform appearance, which is typically achieved by use of optical diffusers. As the color variation increases, however, a larger mixing distance and/or stronger optical diffusers, which increase light loss, are needed to achieve a uniform appearance.

FIG. 1Aillustrates an example embodiment of a lighting device that combines two or more primaries and achieves a uniform appearance of light. The lighting device100ofFIG. 1Aincludes a first LED110and a second LED120. First LED110and second LED120may be mounted on a mounting surface150of, for instance, a base151. A first phosphor115is disposed over both the first LED110and the second LED120. A second phosphor125is disposed over only the second LED120, such that the second phosphor is disposed between the first phosphor115and the second LED120, and is also disposed between the first LED110and the second LED120. As show inFIG. 1A, the second phosphor125may be in contact with the first phosphor115.

Lighting device100may include sidewalls155, which may surround the lighting device100. The base151and side walls155may be formed by a single lead frame. First LED110and second LED120are mounted within the single lead frame on the mounting surface150of base151. The first LED and second LED may be connected to a power source through the lead frame as is understood by a person having ordinary skill in the art. The first LED and second LED may have a common anode, common cathode or each have an individually addressable anode and cathode.

The first phosphor115forms a light emitting surface140on lighting device100that is opposite to the first LED110and second LED125, and opposite to the mounting surface150. The entire light emitting surface may be formed from an optically uniform material composed of the first phosphor115. The light emitting surface140may be continuous, unbroken, and regular across the entire surface. The light emitting surface140may be substantially flat. The light emitting surface140may entirely fill an area contained within sidewalls151, for instance, within a lead frame package. The light emitting surface140is the surface through which light output by the first LED110and second LED120exits the lighting device100, creating a uniform source appearance due to the scattering properties of the first phosphor115.

FIG. 1Billustrates the light path through lighting device100. First LED110is configured to emit a first light170which enters the first phosphor115. At least a portion of first light170is absorbed by first phosphor115, which down-converts the portion of first light170to a second light172. Second light172has longer wavelengths than first light170. Second light172exits lighting device100through the light emitting surface140.

First phosphor115may be formed such that a portion of first light170emitted from the first LED enters the first phosphor115and is not down-converted by phosphor115. The unconverted first light174passes through the first phosphor115and exits the light emitting surface140having the same range of wavelengths as the first light170.

Second LED120is configured to emit a third light180, which enters the second phosphor125. At least a portion of third light180is absorbed by the second phosphor125, which down-converts the portion of third light180to a fourth light182. Fourth light182has longer wavelengths than third light180. Fourth light182enters the first phosphor115from the second phosphor125.

The first phosphor115and second phosphor125may be chosen so that the fourth light182is not absorbed by the first phosphor115, in which case fourth light182passes through the first phosphor115and exits lighting device100through the light emitting surface140.

Second phosphor125may be formed such that a portion of third light180emitted from the second LED120enters the second phosphor125and is not down-converted by phosphor125. The unconverted third light184has the same range of wavelengths as third light180. The unconverted third light184enters the first phosphor115from the second phosphor125. Upon entering the first phosphor115, a portion of the unconverted third light184may remain unconverted. In such case any unconverted third light184not further converted by the first phosphor115exits the light emitting surface having the same range of wavelengths as the second light180. Depending on the wavelength range of third light180and the characteristics of the first phosphor, unconverted third light184, or a portion thereof, may be absorbed by first phosphor115, and down-converted to light188having longer wavelengths than unconverted third light184, and which may have a same range of wavelengths as second light172.

The second light172, unconverted first light174, fourth light182, and any unconverted third light184and light188, combine to form the desired color or white light CCT value of the lighting device100. The second light172, unconverted first light174, fourth light182, as well as any unconverted third light184and light188, pass through at least a portion of the first phosphor115and through the light emitting surface140, which gives lighting device100the appearance of a uniform color of light, due to the scattering properties of the first phosphor115and because the light is emitted through the single surface of uniform material, instead of through discrete LED packages. All of the light that leaves the lighting device100passes through some portion of the first phosphor115and through the uniform light emitting surface140.

First phosphor115and second phosphor125may be arranged to convert different amounts of first light170and third light180. Second phosphor125may be arranged such that most or all of the third light180is down-converted by the second phosphor125, and none of, or only a small portion of third light180is not down-converted by second phosphor125. That is, little or no unconverted third light184enters the first phosphor115. For example, the second phosphor125may convert more than 90% of third light180to fourth light182, and 10% or less of third light180may enter the first phosphor115as unconverted third light184. For example, second phosphor may convert more than 97% of third light180to fourth light182, and 3% or less of third light180may enter the first phosphor115as unconverted third light184. Increasing the amount of conversion of third light180reduces the effect of the first phosphor115on the color points, so that the first phosphor115mostly causes scattering of fourth light182.

This difference in conversion between the first phosphor115and second phosphor125can be observed in the light output by lighting device100. The “first primary” of lighting device100is defined as light emitted by first LED110that passes through first phosphor115and exits lighting device100through light emitting surface140, (that is, second light172and unconverted second light174). The “second primary” of lighting device100is defined as light from the second LED120that passes through the second phosphor125and then first phosphor115, and exits lighting device100through the light emitting surface140, (that is fourth light182and any unconverted third light186and light188that exits the lighting device100). If the first light170emitted by the first LED110has a first wavelength range, the spectral power distribution of the second primary may contain less than 3% of the total radiant power within the wavelength ranges of the unconverted second light174(i.e., within the first wavelength range). The spectral power distribution of the first primary, may have at least 25% of total radiant power within the wavelength ranges of the unconverted second light174(i.e., within the first wavelength range). The second phosphor125is arranged so that this difference in spectral power distribution between the first and second primaries remains even when the second LED120is configured to emit light in the first wavelength range, i.e., within the same wavelength range as the first LED110.

Any appropriate method may be used to form first phosphor115and second phosphor125. For example, first phosphor115may be formed by mixing a first phosphor material into a carrier material, such as silicone, to form a silicone slurry. Second phosphor125may be formed separately by mixing a second phosphor material into a carrier material, such as a silicone, to also form a silicone slurry. The second phosphor125mixture of the second phosphor material and carrier is deposited over the second LED120mounted on mounting frame150to form second phosphor125. The second phosphor125mixture of the second phosphor material and carrier is deposited in such a way that it is contained over and around the second LED120(methods for containment of the second phosphor are described in more detail below with respect toFIG. 2andFIG. 4). After the second phosphor125mixture is deposited, the first phosphor115mixture is deposited over the first LED110mounted on mounting surface150, the second phosphor125and the second LED120.

In another example method for forming first phosphor115and second phosphor125, the carrier is a ceramic, and the phosphor material is mixed into the ceramic and formed into a ceramic platelet. The ceramic platelet of the second phosphor125is sized to cover the second LED120, and is then positioned on the second LED120, but not the first LED110. The ceramic platelet of the first phosphor115is sized to cover both the first LED110and the second LED120, and is positioned over the first LED110, the second phosphor125ceramic plate, and the second LED120, such that the second phosphor125ceramic plate is positioned between the second LED120and the first phosphor115ceramic plate. If the first phosphor115and second phosphor125are formed as ceramic platelets, they may or may not be formed so as to also be positioned between first LED110and second LED120, but the two LEDs may instead be separated by an optical barrier, so the that ceramic platelets are positioned only on the top of the LEDs.

A person having ordinary skill in the art will understand how to achieve the difference in conversion between the first phosphor115and second phosphor125described above. For example, the first phosphor115may have a lower concentration of phosphor material than the second phosphor125, which concentration of phosphor material will depend on the particular phosphor material used. The size of the phosphor particle in the phosphor material used can also be used to adjust the extent of conversion.

The first phosphor115may also include a scattering agent, for example scattering particles such as TiO2or ZrO2to enhance the scattering performance of the first phosphor115and further increase the uniformity of light.

Any LED may be used as first LED110and second LED120depending on the desired color or white light CCT, and if applicable, the desired tuning range, of the lighting device100. For instance, first LED110and second LED120may be semiconductor diodes structures, or LED dies, such as III-nitride LEDs based on the InGaN materials system. First LED110and second LED120may be the same, emitting first light170and third light180having the same wavelength range, or first LED110and second LED120may be different, and first light170may have a different wavelength range than third light180.

The particular LEDs and particular phosphor materials chosen for use in lighting device100are selected to provide the desired color or white light CCT value of the lighting device, or range of colors and white light CCTs of lighting device100if lighting device100is tunable.

The lighting device100may configured to be tunable by varying the driving current provided to the first LED110and second LED120, such that the color or white light CCT value varies as more or less first light170and third light180are emitted. Because all light emitted from the lighting device100is emitted through the light emitting surface140, the light has a uniform appearance even as the different primaries are mixed to form different colors or white light CCT values.

Lighting devices as disclosed herein may be useful for producing a tunable white light lighting device having a uniform appearance. Such a lighting device may be made, for example, in a single LED package (a single lead frame) with three phosphor-converted colors that serve as the primaries for the color-tunable lighting device.

FIG. 2illustrates a lighting device200useful for producing white light lighting devices in a single LED package, including white light lighting devices in a single LED package that are tunable between varying white light CCT values. The lead frame260contains first LED210, second LED220and third LED230disposed on mounting surface250. Second phosphor225is disposed over second LED220. Third phosphor235is disposed over third LED230. The first phosphor215is disposed over the first LED210, the second phosphor225and second LED210, and the third phosphor235and third LED230. The first phosphor215is disposed between the first LED210and the second LED220, as well as between the first LED210and the third LED230. The second phosphor225is disposed between the first phosphor215and the second LED220. The third phosphor235is disposed between the first phosphor215and the first LED210.

The first phosphor215covers the entire surface of the lead frame260LED package, to form the light emitting surface240, which creates a uniform appearance of the light due to the scattering properties of the first phosphor215, as described above with respect toFIGS. 1A and 1B.

Similar to the second LED120and second phosphor inFIG. 1B, the third LED230is configured to emit light, a fifth light, which is absorbed, or mostly absorbed, by third phosphor235and down-converted to a sixth light having longer wavelengths than the fifth light. The sixth light exits the third phosphor235and enters and passes through the first phosphor215. The light emitted by the lighting device200through the light emitting surface240includes the sixth light, in addition to light emitted and down converted from the first LED210and first phosphor215, and second LED220and second phosphor225, and any unconverted light, as described above with respect toFIG. 1B.

The first LED210, second LED220, third LED230, first phosphor215, second phosphor225, and third phosphor235may be selected to produce white light with a tunable CCT. For example, reference is made to U.S. patent application Ser. No. 16/431,094, titled “LED and Phosphor Combinations for High Luminous Efficacy Lighting with Superior Color Control,” for a detailed description of white light tuning with desaturated RGB primaries (incorporated herein by reference). The first LED210, second LED220, and third LED230may be LED dies configured to emit violet or blue light with a peak wavelength in the range of 400-460 nm. The phosphor mixtures may have different compositions of green and/or red phosphors. In particular, for example, second phosphor225may include a red phosphor material, and third phosphor235may include a green phosphor material. The first phosphor115may also include a green phosphor material, but at a low enough concentration that the combination of the unconverted first light emitted by LED210, and second light converted by the first phosphor215is substantially blue, that is, has a peak wavelength in the range of 400-460 nm (as shown, for example, inFIG. 3described below). The light emitted by each LED die210,220, and230is at least partly down-converted by the respective phosphors215,225,235to longer wavelengths; thus, three primary spectra are formed. For example, the three primary spectra for such a white light lighting device200may have substantially blue, red, and green color points and other spectral characteristics described in more detail in U.S. patent application Ser. No. 16/431,094.FIG. 3shows example primary spectra of blue301, red,302, and green303. The red and green primaries, those emitted from second LED220through the second phosphor225, and third LED230through third phosphor235, are almost fully converted. Therefore, having the light from those primaries pass through the first phosphor215of the blue primary has very little effect on the red and green primary color points and results mostly in scattering. This property is utilized in the embodiments of this disclosure by having the first phosphor215cover the entire light emitting surface240of the LED package260, to create a uniform source appearance.

As described above, the light from first LED210that passes through the first phosphor115that forms the light emitting surface240is less converted than that from the second and third LEDs220,230underneath the first phosphor215and, respectively, the second phosphor225and third phosphor235. Preferably, primary spectra of the light emitted by the second LED220and third LED230and having passed through the second phosphor225and third phosphor235, respectively, and the first phosphor215to exit the lighting device200through the light emitting surface240have a spectral power distribution that contains less than 3% of total radiant power in the wavelength range of 400-460 nm of the LED dies used for the first, second and third LEDs210,220, and230, and the primary spectra of the light emitted by the first LED210and having passed through the first phosphor215to exit the lighting device200through the light emitting surface240has a spectral power distribution with more than 25% of total radiant power in this wavelength range (400-460 nm).

Lighting device200may be formed by forming three mixtures of phosphor materials dispensed in a silicone carrier to form a silicone slurry, one for each of the first, second, and third phosphor215,225, and235, respectively. The second phosphor225mixture and third phosphor235mixture, which are the red and green phosphor silicone slurries, respectively, are deposited on top of the respective LED dies,220,230, and are contained over and around the respective LED dies220,230due to surface tension and viscosity of the silicon slurry. After being deposited on the respective LED dies,220,230, the red phosphor and green phosphor silicone slurries may be partially or fully cured to preserve the shape of the deposited phosphor silicone slurry and to also help contain the phosphor silicone slurries over the respective LEDs. The mixture of the first phosphor material dispensed in a silicon slurry is then deposited over the first LED210, and the second and third phosphors225and235, and fills the cavity263of the lead frame260LED package.

FIGS. 4A and 4Billustrate, respectively, a cross-sectional view and a plan view of a lighting device400which utilizes an alternative method for containing the separate phosphors. In lighting device400, the mounting surface450of lead package460is shaped to include inner walls (or dams)470,471inside the main cavity463of the lead frame460LED package. The first LED410is disposed on the mounting surface450of the lead package460between two the inner walls470,471. The second LED420is disposed on mounting surface450between inner wall471and the sidewall451of lead frame460. The third LED430is disposed on mounting surface450between inner wall470and sidewall451of lead frame460. A mixture of the second phosphor material and silicone slurry used to form second phosphor425is deposited over the second LED420and between the inner wall471and sidewall451, such that the mixture is contained by the inner wall471and sidewall451. Similarly, a mixture of the third phosphor material and carrier, such as a silicone slurry, used to form the third phosphor435is deposited over the third LED430and between inner wall470and sidewall451, such that the mixture is contained between inner wall470and sidewall451. A mixture of the first phosphor material and carrier, such as a silicon slurry, used to form the first phosphor415is then deposited over the first LED410to fill the cavity463between sidewalls451, covering the second phosphor425and third phosphor435, and forming light emitting surface440.

FIG. 4Billustrates a plan view of lighting device400. The lead frame460is rectangular. The inner walls470,471divide the cavity463into three rectangular wells481,482, and483which contain, respectively, the first LED410, second LED420, and third LED430. Second phosphor425is disposed within second well482and third phosphor435is contained within third well483. First phosphor415fills the first well481and the remainder of the cavity, forming the light emitting surface440within light emitting surface edge441.

Lighting devices according to the disclosure may have a variety of different geometries.FIG. 5illustrates a lighting device500having a circular geometry. In lighting device500there are three inner walls570,571, and572. The three inner walls570,571, and572divide the circular cavity563in lead frame560into three wells,581,582, and583which contain, respectively, the first LED510, second LED520, and third LED530. The three wells581,582, and583are shown inFIG. 5as having approximately equal volume, however, any suitable relationship of volumes may be used. Two inner walls570and572, along with the sidewall551of lead frame560contain the third phosphor235. Two inner walls572and571, along with the sidewall551of the lead frame560contain the second phosphor225.

In addition to providing a uniform light source, another advantage of the lighting device disclosed herein, is that it allows all of the primaries to be contained within a single LED package, which reduces the size of the device as compared to using multiple LED packages, and also simplifies the use of the device. For instance, a three primary conventional white light source would need three individual LED packages, one for red, green, and blue, which may be 3.5 mm×2.8 mm each. In the lighting devices disclosed herein, for instance lighting devices400(FIGS. 4A and 4B) and500(FIG. 5), all three primaries are contained in a single LED package which may be 3.0 mm×3.0 mm, which is significantly smaller. The size is further reduced because there is no need for additional optics that are required when the individual LED packages are used for each color to create uniform light.

Although described above in terms of red, green and blue primaries, in other embodiments primaries having different colors, and/or additional primaries may be employed. For example, a fourth LED may be included having a fourth phosphor also situated over the fourth LED and under the first phosphor material may be used. Any number of primaries (>1) may be used.

Other implementations of the lighting device disclosed herein, in addition to the single lead frame LED package disclosed above, may be utilized. For example, each of the first LED, second LED, and third LED may be a group of LEDs, which may be utilized in, for example, a chip-on-board configuration. A chip-on-board configuration may include an array of LED dies, e.g. 36 dies, 96 dies, 450 dies and up, mounted onto a metal-core printed circuit board. In such a chip-on-board configuration which uses three primaries, the group of second LED dies and group of third LED dies are covered by a second and third phosphor, respectively, and the group of first LED dies is covered by a first phosphor which also covers the second and third phosphors and the second and third group of LED dies.

This disclosure is illustrative and not limiting. Further modifications will be apparent to one skilled in the art in light of this disclosure and are intended to fall within the scope of the appended claims.