Patent Description:
Light emitting diodes (LEDs) are widely known in lighting and display devices as a replacement for traditional incandescent bulbs and/or fluorescent lighting. It is desirable to generate white light with high color purity at high efficiency.

There are two main approaches to generating white light from an LED. The first is to use a combination of multiple LEDs with different emission color s at different intensities. For example, blue, red and green emitting LEDs can be combined to produce white light. However, a problem with this approach is that the spectral power distribution of the component LEDs may be relatively narrow i.e., may have a full width half maximum (FWHM) of approximately between <NUM>-<NUM>. Wavelength ranges, therefore, exist in which it may be difficult to obtain high efficiency e.g. <NUM>.

The other main approach is to use a single color LED (with emission at a particular wavelength) in combination with a wavelength conversion material such as a phosphor. In this way, the wavelength conversion material absorbs light from the LED of a particular wavelength and emits the light at a different wavelength, normally at a longer wavelength (i.e. of lower energy). For example, a blue LED could be used with a yellow-green phosphor. However, there are currently limits to the efficiencies achieved using this method.

Typical white light emitting devices have efficiencies in the range of <NUM>-<NUM> lm/W and the current densities of the LED chips required to achieve these efficiencies are relatively high (typically between <NUM> to <NUM> A/mm<NUM>). Accordingly, there is a need for a high efficiency white light emitting device using LEDs that does not suffer from the aforementioned problems.

In <CIT> wavelength conversion member is provided in which the following are dispersed in a thermoplastic resin: a LuYAG fluorescent material that is represented by (Y<NUM>-a- beta LuaCe beta )<NUM>Al<NUM>O<NUM>, that emits yellow-green light as a result of excitation by blue light, and a KSF fluorescent material that is represented by K<NUM>(Si<NUM>-xMnx)F<NUM> and that emits red light as a result of excitation by blue light. The content of the KSF fluorescent material in the wavelength conversion member is <NUM> to <NUM> times the content of the LuYAG fluorescent material by mass ratio. The wavelength conversion member makes it possible to provide a light-emitting device that has small color deviation, that is suitable as a lighting device, that emits white light, and that has good color rendering properties in a color temperature range of <NUM>,<NUM>-<NUM>,<NUM>, i.e., the color temperature range from white to daylight color.

<CIT> discloses an LED-filament comprising: a partially light-transmissive substrate; an array of LED chips on a front face of the substrate; first broad-band green to red photoluminescence materials and a first narrow-band manganese-activated fluoride red photoluminescence material covering the array of LED chips and the front face of the substrate; and second broad-band green to red photoluminescence materials covering the back face of the substrate. The LED-filament can comprise: no narrow-band manganese-activated fluoride red photoluminescence material on the back face of the substrate, or a second narrow-band manganese-activated fluoride red photoluminescence material on the back face of the substrate in an amount up to <NUM> wt percent of a total red photoluminescence material content on the back face of the substrate.

The invention in <CIT> provides a lighting device, configured to provide lighting device light, the lighting device comprising: - one or more light sources configured to provide light source radiation comprising deep blue radiation in the range of <NUM>-<NUM> and blue light in the range of <NUM>-<NUM>; - a first luminescent material configured to convert at least part of the light source radiation into first luminescent material light with light intensity in one or more of the green spectral region and yellow spectral region; a second luminescent material configured to convert (i) at least part of the light source radiation, or (ii) at least part of the light source radiation and at least part of the first luminescent material light into second luminescent material light with light intensity in the red spectral region, wherein the second luminescent material comprises a red luminescent material showing under excitation with at least part of the light source radiation, or (ii) at least part of the light source radiation and at least part of the first luminescent material light an emission in the range of <NUM>-<NUM>; wherein the lighting device is configured to provide at a first setting of the lighting device white lighting device light comprising deep blue radiation, blue light, first luminescent material light and second luminescent material light.

In light of this, an efficient white light emitting device is provided according to the claims. In a first aspect of the invention, 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 <NUM> to <NUM>; and a phosphor material composition comprising: a yellow green phosphor material which generates light with a peak emission wavelength in a range <NUM> to <NUM>; and a narrow band red phosphor material which generates light with a peak emission wavelength in a range <NUM> to <NUM>; wherein the phosphor material composition comprises the narrow band red phosphor material in an amount of from <NUM> to <NUM> wt. % for a CCT of from <NUM> to <NUM> or in an amount of from <NUM> to <NUM> wt. % for a CCT of from <NUM> to <NUM> CCT; and wherein the device is adapted to generate a white light output with an efficiency of at least <NUM> Im/W at a blue LED chip input current density in a range from <NUM> to <NUM> mA/mm<NUM>, preferably in the range from <NUM> to <NUM> mA/mm<NUM> and more preferably in the range from <NUM> to <NUM> mA/mm<NUM>.

Embodiments of the device have a high efficiency at a low LED input current density. This therefore provides a white LED that is significantly more efficient than existing LEDs (<NUM>-200lm/W) while also providing the required light color for general lighting applications. For example, the efficiency can be <NUM> Im/W to <NUM> lm/W, for example <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM> Im/W. As set out below, embodiments provide this improvement through use of a blue LED chip that is more efficient through application of the specific current density and the improvement of the white spectrum efficiency through the use of the recited narrow band red phosphor amounts in a wavelength conversion phosphor material (e.g. covering the blue LED chips so as to modify the wavelength of the light).

The main components relating to the white LED device efficiency (Lm/Wwhite) are shown in the below equation: <MAT>.

The efficiency of the device measured in lumens/watt and can be calculated by standard LED photometric techniques.

Referring to the first and second components of the white LED device efficiency mentioned above in equation (<NUM>), the combination of the blue LED chips at a low current density in a range from <NUM> to <NUM> mA/mm<NUM> with the phosphor material composition comprising a narrow band red phosphor in the specified weight percentages for different CCT ranges, contribute to the high efficiency of at least <NUM> Im/W in this device. The specified weight percentages of the narrow band red phosphor materials are important as they determine the ratio of the narrow band red phosphor material to the yellow green phosphor material. The white light emitted from the device is made up of different colored components from the interaction of the blue LED chip with the phosphor materials. By incorporating the narrow band red phosphor materials at the specified weight percentages, the phosphor material composition has been found to provide the improved device efficiency for white light emission.

The narrow band red phosphor material can have a FWHM of ≤ <NUM> in a peak emission wavelength range from <NUM> to <NUM>. Phosphor conversion efficiency is typically lower for broad red emitter phosphors (i.e. those which have a broader spectral emission profile than narrow band red phosphors) compared to green / yellow green phosphors. The narrow spectral profile of a narrow band red band phosphor helps reduce red spectrum efficiency loss at the same time as maintaining a high color rendering index (CRI). The CRI is a measure of the color purity and is defined as the ability of a light source to accurately illuminate the color of an object as if it were being illuminated by an incandescent bulb or natural light source. It has therefore been found that the specific combination of materials in the device results in the high efficiency of the white light emitting device with high color rendering index.

The weight percentages of the narrow band red phosphor material present in the phosphor material composition are specific depending on the desired correlated color temperature "CCT". The CCT is the temperature of a heated black body radiator with emission that matches the color of a white light source. CCTs in the range of <NUM> to <NUM> are described as warm white with a yellower hue. CCTs of <NUM> to <NUM> are described as neutral white to cool white. As such, in the first aspect, the device is either (i) a device having a CCT of from <NUM> to <NUM> (e.g. emitting light having a CCT of from <NUM> to <NUM>) and the narrow band red phosphor material is present in the composition in an amount of from <NUM> to <NUM> wt. %; or (ii) a device having a CCT of from <NUM> to <NUM> CCT (e.g. emitting light having a CCT of from <NUM> to <NUM>) and the narrow band red phosphor material is present in the composition in an amount of from <NUM> to <NUM> wt. It has been found that this narrower range of narrow band red phosphor material is particularly effective.

In some embodiments, the phosphor material composition comprises the narrow band red phosphor material in an amount of from <NUM> to <NUM> wt. % for a CCT of from <NUM> to <NUM>.

In some embodiments, the phosphor material composition comprises the yellow green phosphor material in an amount of from <NUM> to <NUM> wt. % for a CCT of from <NUM> to <NUM> or from <NUM>-<NUM> wt. % for a CCT of from <NUM> to <NUM>. The ratio of the yellow green phosphor material to the narrow band red phosphor material contributes to the white light color output and therefore the efficiency of the device in embodiments.

In some embodiments, the phosphor material composition comprises the yellow green phosphor material in an amount of from <NUM> to <NUM> wt. % and the narrow band red phosphor material in an amount of is from <NUM> to <NUM> wt. % for a CCT of from <NUM> to <NUM>.

In some embodiments, for a CCT of between <NUM> to <NUM>, the phosphor material composition further comprises a broad spectrum red phosphor material; and for a CCT of between <NUM> to <NUM>, the phosphor material composition comprises: the broad spectrum red phosphor material in an amount of from <NUM> to <NUM> wt. %; the yellow green phosphor material in an amount of from <NUM> to <NUM> wt. %; and the narrow band red phosphor material in an amount of from <NUM> to <NUM> wt.

In embodiments, the broad spectrum red phosphor material refers to a phosphor having a FWHM value of greater than or equal to <NUM> (at an emission range from <NUM> to <NUM>), for example this could be from <NUM>-<NUM>. Incorporation of this broad spectrum red phosphor material (e.g. a nitride phosphor such as CaAlSiN<NUM>:Eu<NUM>+ or Sr<NUM>Si<NUM>N<NUM>:Eu<NUM>+) into the phosphor composition is advantageous at the specified CCT ranges of between <NUM>-<NUM> to contribute to the provision of warmer white emission from devices.

In some embodiments, the phosphor material composition comprises the narrow band red phosphor material in an amount of: from <NUM> to <NUM> wt. % for a CCT of <NUM>; from <NUM> to <NUM> wt. % for a CCT of <NUM>; from <NUM> to <NUM> wt. % for a CCT of <NUM>; or from <NUM> to <NUM> wt. % for a CCT of <NUM>. These embodiments have been found to be particularly efficient for each respective CCT.

In some embodiments, the ccy position of the white light output is in a range <NUM>-<NUM> higher than the blackbody curve. The chromaticity of a particular light source may be referred to as the "color point" which has coordinates (ccx, ccy) in the CIE (Commission Internationale de l'eclairage in French, or International Commission on Illumination in English) color space diagram. In terms of white light, the "white point" may fall along a locus of chromaticity points corresponding to the color of light emitted by a black body radiator heated to a given temperature. This locus is termed the black body locus or BBL. It has been found that the specified increase of the ccy coordinate <NUM>-<NUM> above the BBL in this device can contribute to an improved efficiency. This efficiency of the device is improved as, at the specified ccy coordinate increase, the contribution from the yellow green phosphor emission is higher than that for the blackbody curve. Yellow green emission has high phosphor conversion efficiency and therefore, as this contribution is increased, the overall device efficiency is increased.

In embodiments, the white light (output) may be above the BBL and at a distance to the BBL of at least <NUM> SDCM, preferably at least <NUM> SDCM, more preferably at least <NUM> SDCM, even more preferably at least <NUM> SDCM, most preferably at least <NUM> SDCM. The obtained effect is improved performance of the white light emitting device according to the invention. The reason is that high quality white light (output) is obtained with a (relatively) low amount of red light in the white light. In this way, issues regarding quencing (of the red phosphor) is (further) reduced.

In embodiments, the white light (output) may have a color rendering index of at least <NUM>, preferably at least <NUM>, more preferably at least <NUM>, most preferably at least <NUM>. The white light emitting device according to the invention is particular suitable for achieving this high quality of light.

In some embodiments, the substrate and the string of blue LED chips are arranged as a LED filament. To generate sufficient lumen output, multiple blue LED chips on the substrate are needed and LED filaments have high design flexibility for chip size and substrate material combination. Incorporating an LED filament in the device can mimic the traditional configuration of an incandescent bulb, but with much improved efficiency. The use of a LED filament in embodiments is particularly beneficial as the efficiency is significantly improved without requiring, for example, a large heatsink. The efficiency associated with these LED filaments is, in part, owing to the presence of multiple smaller, lower-power LED chips than traditional LED filaments. Accordingly, it has been found that LED filament/filaments can contribute to higher efficiency of the device through lower driving currents.

A LED filament is providing LED filament light and comprises a plurality of light emitting diodes (LEDs) arranged in a linear array. Preferably, the LED filament has a length L and a width W, wherein L>5W. The LED filament may be arranged in a straight configuration or in a non-straight configuration such as for example a curved configuration, a 2D/3D spiral or a helix. Preferably, the LEDs are arranged on an elongated carrier like for instance a substrate, that may be rigid (made from e.g. a polymer, glass, quartz, metal or sapphire) or flexible (e.g. made of a polymer or metal e.g. a film or foil).

In case the carrier comprises a first major surface and an opposite second major surface, the LEDs are arranged on at least one of these surfaces. The carrier may be reflective or light transmissive, such as translucent and preferably transparent.

The LED filament may comprise an encapsulant at least partly covering at least part of the plurality of LEDs. The encapsulant may also at least partly cover at least one of the first major or second major surface. The encapsulant may be a polymer material which may be flexible such as for example a silicone. Further, the LEDs may be arranged for emitting LED light e.g. of different colors or spectrums. The encapsulant may comprise a luminescent material that is configured to at least partly convert LED light into converted light. The luminescent material may be a phosphor such as an inorganic phosphor and/or quantum dots or rods.

The LED filament may comprise multiple sub-filaments.

In some embodiments, the LED filament comprises a sapphire substrate. It has been found that sapphire substrates are particularly effective and can help to provide an additional efficiency to the device.

Each of the blue LED chips in the device can generate an output flux in the range 2lm to 4lm. For example, one blue LED chip can contribute around 3lm flux output to the device.

In some embodiments, the device further comprises an encapsulant over the blue LED chips which encapsulant comprises the phosphor material composition. The encapsulant can help to seal the phosphor material composition in close proximity to the blue LED chip.

In some embodiments, the yellow green phosphor material comprises yttrium aluminum garnet (YAG), gallium modified yttrium aluminum garnet GaYAG or lutetium modified yttrium aluminum garnet LuYAG. In some embodiments, the narrow band red phosphor material comprises K<NUM>SiF<NUM>:Mn<NUM>+ (KSF). The KSF phosphor is relatively sensitive for high temperatures as the phosphor is susceptible for degradation at elevated temperatures. An advantage of the present invention is that as a result of the relatively low LED chip input current density, the LED chip has a relatively low temperature during operation of the white light emitting device.

In some embodiments, for a CCT of between <NUM> to <NUM>, the accumulated spectrum intensity ratio from <NUM> to <NUM> is higher than <NUM>% of the total white spectrum from <NUM> to <NUM>; or for a CCT of between <NUM> to <NUM>, the accumulated spectrum intensity ratio from <NUM> to <NUM> is higher than <NUM>% of the total white spectrum.

In some embodiments, the blue LED chip size is in the range <NUM><NUM> to <NUM><NUM>. It has been found that this is the optimal size range for the blue LED chips in the device to contribute to the high efficiency.

In some embodiments, wherein the device comprises either two or three electrodes provided on the substrate. This type of arrangement can be termed a two-finger or three-finger layout. It has been found that by arranging electrodes on the substrate in this way, the forward voltage, Vf, can be reduced. Typically, the greater the number of electrode tracks/fingers, the lower the Vf. There is, however, a fine balance between the reduction in the forward voltage and an increase in forbidden light excitation. Embodiments providing two tracks have been found to be particularly efficient.

In some embodiments, the blue LED chip to chip distance is equal or greater than <NUM>. The blue-chip emitting pattern is omnidirectional and therefore, by having the chip to chip distance of greater than or equal to <NUM>, the efficiency can be greatly improved. It has been found that at this distance, side emitting blue light absorbance by an adjacent chip is reduced. As a result, the PEwhite is increased which contributes to the overall efficiency of the device discussed with reference to equation (<NUM>). This may be, for example, greater than or equal to <NUM> and less than <NUM>. For example, the distance could be in the range of <NUM> to <NUM>, <NUM> to <NUM> or <NUM> to less than <NUM>. The distance can be any value within these ranges, e.g. <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>. In an embodiment, the blue LED chip to chip distance is equal or greater than <NUM>.

In a second 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 <NUM> to <NUM>, wherein each blue LED chip is separated from an adjacent blue LED chip by a blue LED chip to chip distance; and a phosphor material composition comprising: a yellow green phosphor material which generates light with a peak emission wavelength in a range <NUM> to <NUM>; and a narrow band red phosphor material which generates light with a peak emission wavelength in a range <NUM> to <NUM>, wherein the blue LED chip to chip distance is equal or greater than <NUM>. This can generate a white light output with an efficiency of at least 230lm/W at a blue LED chip input current density in a range from <NUM> to <NUM> mA/mm<NUM>, preferably in the range from <NUM> to <NUM> mA/mm<NUM> and more preferably in the range from <NUM> to <NUM> mA/mm<NUM>.

In some embodiments, the phosphor material composition comprises the narrow band red phosphor material in an amount of from <NUM> to <NUM> wt. % for a CCT of from <NUM> to <NUM> or in an amount of from <NUM> to <NUM> wt. % for a CCT of from <NUM> to <NUM> CCT.

The combination of the blue LED chip spacing and the narrow band red phosphor material weight percentages has been found to contribute to high efficiency of the device in this aspect. As discussed above, the specific narrow band red phosphor material weight percentages determine the ratio of the yellow green to narrow band red phosphor in the phosphor material composition. Moreover, when the blue LED chip spacing distance is greater than or equal to <NUM>, the side emitting blue light absorbance by another chip is reduced and the packaging efficiency of the device is increased according to equation (<NUM>). Accordingly, it has been found that, at the resulting yellow green: narrow band red ratios, when the blue LED chip spacing is greater than or equal to <NUM>, the overall efficiency of the device is extremely high.

In some embodiments, the phosphor converted efficiency (CEphosphor) can be enhanced by optimizing the phosphor recipe to increase the green relative spectrum ratio. Because green spectrum has a higher weight percentage of eye sensitive function, the calculated lumen output and efficiency is higher than normal white spectrum. The white spectrum color coordinate is calculated by the spectrum ratio of red/green/blue spectrum. Higher green spectrum content will lead to the LED having relatively higher y coordinate than normal white spectrum. In our study, the white LED efficiency can have <NUM>-<NUM> percentage improvement while shifting the y-coordinate <NUM> - <NUM> higher than the center in y-coordinate at <NUM> defined in ANSI standard C78.

ANSI standard C78. <NUM> is American National Standard for Electric Lamps - Specifications for the Chromaticity of Solid-State Lighting Products. Referring to Section <NUM>, Chromaticity, the chromaticity coordinates and correlated color temperature (CCT) values used are based on the CIE colorimetry system. While the chromaticity of light is expressed by chromaticity coordinates such as (x, y). The chromaticity of nominally white light can also be expressed by CCT and the distance from the Planckian locus. In present disclosure, CIE <NUM> (x-y) Diagram is used.

The coverage of higher y-coordinate color points can be described as below: <MAT> and <MAT>.

This can generate a white light output with an efficiency of at least 230lm/W at a blue LED chip input current density in a range from <NUM> to <NUM> mA/mm<NUM> and preferably from <NUM> to <NUM> mA/mm<NUM>.

In some embodiments, the defined higher y-coordinate color points coverage can be described by MacAdam ellipses according to ANSI C78. MacAdam ellipses is a common language to define white color points coverage. The Macadam ellipses coverage can be defined with below parameters, including reference point color coordinate (Reference x, Reference y), the ellipse parameters (G11/G12/G22), SDCM size (K). Because different CCT have different reference point, the formula of Macadam ellipses coverage is: <MAT> <MAT> <MAT> <MAT>.

Yet further, in embodiments the correlated color temperature (CCT) is especially within about <NUM> SDCM (standard deviation of color matching) from the BBL (black body locus), especially within about <NUM> SDCM from the BBL, even more especially within about <NUM> SDCM from the BBL (black body locus) or blackbody curve.

Another method to describe MacAdam ellipses coverage is to use SDCM size (K), the ellipse major axis (a), the ellipse minor axis (b), the ellipse rotation angle(θ). The translation formula between G1 <NUM>/G12/G22 vs. a/b/ <NUM> be listed below.

The MacAdam ellipses coverage is changed with CCT, below is the examplar coverage of higher y-coordinate color points for various CCT ranges.

The term "luminescent material" herein especially relates to inorganic luminescent materials, which are also sometimes indicated as phosphors. These terms are known to the person skilled in the art.

In embodiments, quantum dots may be applied, and may optionally be embedded in transmissive matrices like e.g. polymers, like PMMA, or polysiloxanes, etc. etc. Quantum dots are small crystals of semiconducting material generally having a width or diameter of only a few nanometers. When excited by incident light, a quantum dot emits light of a color determined by the size and material of the crystal. Light of a particular color can therefore be produced by adapting the size of the dots. Most known quantum dots with emission in the visible range are based on cadmium selenide (CdSe) with a shell such as cadmium sulfide (CdS) and zinc sulfide (ZnS). Cadmium free quantum dots such as indium phosphide (InP), and copper indium sulfide (CuInS<NUM>) and/or silver indium sulfide (AgInS<NUM>) can also be used. Quantum dots show very narrow emission band and thus they show saturated colors. Furthermore, the emission color can easily be tuned by adapting the size of the quantum dots. Any type of quantum dot known in the art may be used in the present invention. However, it may be preferred for reasons of environmental safety and concern to use cadmium-free quantum dots or at least quantum dots having a very low cadmium content. Instead of quantum dots or in addition to quantum dots, also other quantum confinement structures may be used. The term "quantum confinement structures" should, in the context of the present application, be understood as e.g. quantum wells, quantum dots, quantum rods, tripods, tetrapods, or nano-wires, etcetera.

Especially, the luminescent material is configured to convert at least part of the light source light into luminescent material light having an emission band having wavelengths in one or more of (a) the green spectral wavelength range and (b) the yellow spectral wavelength range, wherein the luminescent material comprises a (garnet) luminescent material of the type A<NUM>B5O<NUM>:Ce, wherein A comprises one or more of Y, La, Gd, Tb and Lu, and wherein B comprises one or more of Al, Ga, In and Sc. Hence, the luminescent material light may e.g. green light or yellow light (or in specific embodiments even orange (dependent upon the composition of the garnet and cerium concentration)). However, other embodiments are also possible, see below. In embodiments, <NUM>-<NUM>% of the A elements comprise Ce, even more especially <NUM>-<NUM>%, such as <NUM>-<NUM>%. Especially, embodiments, <NUM>-<NUM>% of the A elements comprise Ce, such as up to <NUM>%, like selected from the range of <NUM>-<NUM>%, such as at least above <NUM>%.

Alternatively or additionally, the luminescent material may e.g. be M<NUM>Si<NUM>N<NUM>:Eu<NUM>+ and/or MAlSiN<NUM>:Eu<NUM>+ and/or Ca<NUM>AlSi<NUM>O<NUM>N<NUM>:Eu<NUM>+, etc., wherein M comprises one or more of Ba, Sr and Ca, especially in embodiments at least Sr. In specific embodiments, the first luminescent may comprise one or more materials selected from the group consisting of (Ba,Sr,Ca)S:Eu, (Ba,Sr,Ca)AlSiN<NUM>:Eu and (Ba,Sr,Ca)<NUM>Si<NUM>N<NUM>:Eu. In these compounds, europium (Eu) is substantially or only divalent, and replaces one or more of the indicated divalent cations. In general, Eu will not be present in amounts larger than <NUM>% of the cation; its presence will especially be in the range of about <NUM> to <NUM>%, more especially in the range of about <NUM> to <NUM>% relative to the cation(s) it replaces. The term ":Eu", indicates that part of the metal ions is replaced by Eu (in these examples by Eu<NUM>+). For instance, assuming <NUM>% Eu in CaAlSiN<NUM>:Eu, the correct formula could be (Ca<NUM>Eu<NUM>)AlSiN<NUM>.

Any of the aspects described above may be provided alone or in combination with any of the embodiments as described above.

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

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 <NUM> to <NUM>; and a phosphor material composition comprising: a yellow green phosphor material which generates light with a peak emission wavelength in a range <NUM> to <NUM>; and a narrow band red phosphor material which generates light with a peak emission wavelength in a range <NUM> to <NUM>; wherein the phosphor material composition comprises the narrow band red phosphor material in an amount of from <NUM> to <NUM> wt. % for a CCT of from <NUM> to <NUM> or in an amount of from <NUM> to <NUM> wt. % for a CCT of from <NUM> to <NUM> CCT; and wherein the device is adapted to generate a white light output with an efficiency of at least 230lm/W at a blue LED chip input current density in a range from <NUM> to <NUM> mA/mm<NUM>.

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.

For narrow band red phosphor, for a CCT of from <NUM> to <NUM>, the weight percentage is from <NUM> to <NUM> wt. For example, the weight percentage can be from <NUM> to <NUM> wt. The weight percentage can also be from <NUM> to <NUM> wt. % in some embodiments. In further embodiments, this can be <NUM> %, for a CCT of <NUM>. The weight percentage can also be from <NUM> to <NUM> wt. %, and, in further embodiments, <NUM> wt. %, for a CCT of from <NUM> to <NUM>. For a CCT of from <NUM> to <NUM>, the weight percentage of the narrow band red phosphor is from <NUM> to <NUM> wt. For example, the weight percentage can be from <NUM> to <NUM> wt. More specifically, the weight percentages of the narrow band red phosphor materials for the corresponding CCTs can be: for <NUM>, between <NUM> to <NUM> wt. % and, in further embodiments, <NUM> wt. %; for <NUM>, between <NUM> to <NUM> wt. % and, in further embodiments, <NUM> wt. %; for <NUM>, between <NUM> to <NUM> wt. % and, in further embodiments, <NUM> wt. %; and for <NUM>, between <NUM> to <NUM> wt. % and, in further embodiments, <NUM> wt.

For the yellow green phosphor material, for a CCT of from <NUM> to <NUM>, the yellow green phosphor weight material percentage can be from <NUM> to <NUM> wt. For a CCT of from <NUM> to <NUM>, the yellow green phosphor material weight percentage can be from <NUM> to <NUM> wt.

Examples of the weight percentages in embodiments of the invention can therefore be, for a CCT of <NUM>, <NUM> wt. % narrow band red phosphor and <NUM> wt. % yellow green phosphor and, for a CCT of <NUM>, <NUM> wt. % narrow band red phosphor and <NUM> wt. % yellow green phosphor.

The weight percentage of the broad spectrum red phosphor material may be from <NUM> to <NUM> wt. For example the weight percentage may be <NUM> wt. An example of a device in accordance with an embodiment of the invention comprising a broad red phosphor for a CCT of <NUM> can therefore comprise: a narrow band red phosphor at <NUM> wt. %; a yellow green phosphor at <NUM> wt. % and a broad spectrum red phosphor at <NUM> wt. An example of another device in accordance with an embodiment of the invention comprising a broad red phosphor for a CCT of <NUM> can comprise: a narrow band red phosphor at <NUM> wt. %; a yellow green phosphor at <NUM> wt. % and a broad spectrum red phosphor at <NUM> wt.

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 <NUM>-<NUM> % efficiency gain owing to their increased transparency (compared to glass or ceramic substrates) which contributes to more backside white light output.

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.

The size of the blue LED chip in embodiments of the invention can also vary. In some cases the size is between <NUM>-<NUM><NUM>. In some embodiments the size of the chip is <NUM><NUM>.

A first embodiment of the invention is shown in <FIG>. A white light emitting device <NUM> comprises blue LED chips <NUM> mounted on a substrate <NUM>. A phosphor material composition comprising a yellow green phosphor material <NUM> and a narrow band red phosphor material <NUM> is deposited over blue LED chips <NUM>. The blue LED chips <NUM> and phosphor material composition of this device are sealed inside the device by an encapsulant <NUM>. Wiring <NUM> is provided to connect blue LEDs <NUM>.

In one specific implementation of the embodiment of <FIG>, the device has a CCT of <NUM> and the phosphor material composition comprises <NUM> wt. % narrow band red phosphor <NUM> and <NUM> wt. % yellow green phosphor <NUM>.

A further embodiment of the invention is shown in <FIG>. A white light emitting device <NUM> comprises blue LED chips <NUM> mounted on a substrate <NUM>. A phosphor material composition comprising: a yellow green phosphor material <NUM>; a narrow band red phosphor material <NUM>; and a broad spectrum red phosphor material <NUM> is deposited over blue LED chips <NUM>. The blue LED chips <NUM> and phosphor material composition of this device are sealed inside the device by an encapsulant <NUM>. Wiring <NUM> is provided to connect blue LEDs <NUM>.

In one specific implementation of the embodiment of <FIG>, the device has a CCT of <NUM> and the phosphor material composition of this embodiment comprises: a narrow band red phosphor at <NUM> wt. %; a yellow green phosphor at <NUM> wt. % and a broad spectrum red phosphor at <NUM> wt.

<FIG> shows a LED filament <NUM> of a white light emitting device. The LED filament <NUM> comprises a substrate <NUM> and a string of blue LED chips <NUM>. The string of blue LED chips <NUM> are mounted onto substrate <NUM>. Each blue LED chip <NUM> has a size of <NUM><NUM> to <NUM><NUM> and is separated from the adjacent blue LED chip <NUM> by a distance d of at least <NUM>.

<FIG> shows a further embodiment of the invention in which a white light emitting device <NUM> comprises four of the LED filaments <NUM> of <FIG>. In alternative embodiments a different number of LED filaments may be used. Although not depicted, the device <NUM> 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 <NUM>. As shown in <FIG> shows the multiple LED filaments <NUM> arranged in a bulb-shaped housing to mimic a traditional incandescent light bulb appearance. Substrate <NUM> is a sapphire substrate.

Alternatively, in a different embodiment, the device <NUM> of <FIG> 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 <NUM>, the phosphor material composition of this embodiment comprises: a narrow band red phosphor at <NUM> wt. %; a yellow green phosphor at <NUM> wt. % and a broad spectrum red phosphor at <NUM> wt.

<FIG> shows two electrodes arranged as two interdigitating elongate tracks <NUM> on a substrate <NUM> of a white light emitting device <NUM>. This arrangement of the electrode tracks is termed a two-finger layout. Two soldering pads <NUM> are arranged on the substrate <NUM> and connect to the interdigitating electrode tracks <NUM>. Alternatively, <FIG> shows three electrodes arranged as three interdigitating elongate tracks <NUM> on a substrate <NUM> of a white light emitting device <NUM>. This arrangement is termed a three-finger layout. Two soldering pads <NUM> are arranged on the substrate <NUM> and connect to the interdigitating electrode tracks <NUM>. In embodiments, white light emitting devices can comprise the two or three-finger layouts <NUM> and <NUM> of <FIG>. Such devices <NUM> and <NUM> 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 <NUM>, the phosphor material compositions of these embodiments comprise <NUM> wt. % narrow band red phosphor and <NUM> wt. % yellow green phosphor.

<FIG> 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 <NUM>-<NUM> mA/mm<NUM> and preferably <NUM>-<NUM> mA/mm<NUM> and in some embodiments it is <NUM> mA/mm<NUM>. 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> 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>, 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>, both around <NUM> and <NUM> mA/mm<NUM> reach <NUM> lm/W, but in <FIG>, the WPE of <NUM> mA/mm<NUM> is higher than that of <NUM> mA/mm<NUM>, 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 togather contribution to the increased lm/W output as high as <NUM> Im/W.

<FIG> 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> 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> 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.

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.

<FIG> shows a spectral power distribution for a device not in accordance with an embodiment of the invention for a CCT of <NUM>. <FIG> 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 <NUM>.

The following are examples of devices in accordance with embodiments of the invention, with the current density and resulting efficiency as shown in <FIG>.

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 (<NUM>).

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

Accordingly, it has been found that a device comprising: a chip size of <NUM><NUM>; a two-finger layout; a chip spacing of greater than <NUM> and an input current density of the blue LED chip at <NUM>. 025A/mm<NUM> can have the highest maximum white LED efficiency point with the specified weight percentages given in Table <NUM>.

<FIG> shows the human eye sensitive function for different color. The green spectrum has highest weight percentage than red or blue colors.

<FIG> show the defined higher y color coordinates coverage above ANSI C78. <NUM> 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. <NUM>, "<NUM>-Step Quadrangles". In <FIG> the CIE <NUM> diagram shows the upper and lower limited color range that have higher ccy coordinate than ANSI C78. <NUM> bin range. In <FIG>, the CIE <NUM> diagram shows examples of MacAdam ellipse ranges according to ANSI standard C78. <NUM> that have higher ccy coordinate than ANSI C78. <NUM> bin range.

<FIG> shows the parameters a/b/θ of a Macadam ellipse.

Claim 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 <NUM> to <NUM>; and
a phosphor material composition comprising:
a yellow green phosphor material which generates light with a peak emission wavelength in a range <NUM> to <NUM>; and
a narrow band red phosphor material which generates light with a peak emission wavelength in a range <NUM> to <NUM>;
wherein the phosphor material composition comprises the narrow band red phosphor material in an amount of from <NUM> to <NUM> wt. % for a CCT of from <NUM> to <NUM> or in an amount of from <NUM> to <NUM> wt. % for a CCT of from <NUM> to <NUM> CCT; and
wherein the device is adapted to generate a white light output with an efficiency of at least <NUM> lm/W at a blue LED chip input current density in a range from <NUM> to <NUM> mA/mm<NUM>.