Patent Description:
White light emitting LEDs ("white LEDs") include one or more photoluminescence materials (typically inorganic phosphor materials), which absorb a portion of the blue light emitted by the LED and re-emit visible light of a different color (wavelength). The portion of the blue light generated by the LED that is not absorbed by the phosphor material combined with the light emitted by the phosphor provides light which appears to the eye as being white in color. Due to their long operating life expectancy (><NUM>,<NUM> hours) and high luminous efficacy (<NUM> lumens per watt and higher), white LEDs are rapidly replacing conventional fluorescent, compact fluorescent and incandescent lamps.

Various metrics exist for quantifying the characteristics and quality of light generated by white lighting sources. The two most commonly used metrics within the solid-state lighting industry are Correlated Color Temperature (CCT) and International Commission on Illumination (CIE) General Color Rendering Index (CRI) Ra.

The CCT of a lighting source is measured in kelvin (K) and is the color temperature of a Plankian (black-body) radiator that radiates light of a color that corresponds to the color of the light generated by the lighting source.

The General CRI Ra characterizes how faithfully a lighting source renders the true colors of an object and is based on a measure of how well a lighting source's illumination of eight color test samples (R1 to R8) compares with the illumination provided by a reference source. In general, the higher the value indicates its closeness to a black radiator and natural sunlight. General CRI Ra can take negative values and has a maximum value of <NUM>. Since the color samples R1 to R8 are all pastel colors (low saturation colors "Light Grayish Red" to "Reddish Purple") the General CRI Ra gives a useful measure of subtle differences in light output of incandescent sources which generate a full spectrum that closely resembles sunlight. However, for white LEDs whose spectrum is composed of peaks, the General CRI Ra is proving to be inadequate as it is an average measure of color rendition over a limited range of colors and gives no information of the lighting source's performance for particular colors or highly saturated colors. Thus, when characterizing full spectrum solid-state white light emitting devices the CRI color samples R9 to R12 (saturated colors "Saturated Red", "Saturated Yellow", "Saturated Green", "Saturated Blue") and R13 to R15 ("Light Skin Tone", "Leaf Green", "Medium Skin Tone") should be taken into account to give a meaningful characterization of full spectrum light.

To address the limitations of General CRI Ra, the Illuminating Engineering Society (IES) recently published the TM-<NUM> standard for measuring and characterizing the color performance of lighting sources (<NPL>). Under the TM-<NUM>-<NUM> standard, two metrics are used to characterize the color rendering characteristics of a lighting source, Fidelity Index (Rf) and Gamut Index (Rg). It is believed that IES TM-<NUM>-<NUM> method has better correlation with people's color perception and, therefore, gives a more accurate characterization of a lighting source's light characteristics. The Fidelity Index Rf is similar to General CRI Ra and characterizes how faithfully a lighting source renders the true colors of an object and is based on a measure of how well a lighting source's illumination of <NUM> color samples compares with the illumination provided by a reference source. The Fidelity Index Rf value ranges from <NUM> to <NUM>. The new color samples have been selected to be more representative of objects that are likely to be encountered in real-life applications and, as a result, the Fidelity Index Rf is believed to be a more accurate measure of color rendering than the General CRI Ra. Since Rf is measured over a greater number of color samples, it will be more difficult to achieve high scores compared with the General CRI Ra. Moreover, due to the different testing procedures, General CRI Ra and Fidelity Index Rf values are not comparable against each other.

The Gamut Index Rg focuses on color saturation and is an average level of saturation compared with a reference source. The Gamut Index correlates to the vividness of the appearance of colored objects. The Gamut Index Rg value ranges from <NUM> to <NUM> where values below <NUM> indicate decreased saturation and values above <NUM> indicate increased saturation compared with the reference source.

A further problem with known white LEDs, that are commonly used in display backlights of cell phones, is the damage they potentially cause to the human eye and particularly in view of ever-increasing screen-time usage. The American Macular Degeneration Foundation (AMDF) have reported that the blue rays of the spectrum appear to accelerate age-related macular degeneration (AMD) more than any other rays in the spectrum. High Energy Visible (HEV) blue light in the region of <NUM> - <NUM> has been identified for years as the most dangerous light for the retina. Almost all visible blue light passes through the cornea and lens and reaches the retina. This light can affect vision and can prematurely age the eyes. Early research shows that too much exposure to blue light (HEV) can lead to digital eyestrain and retinal damage. This can cause vision problems such as age-related macular degeneration. This damage occurs when blue light (HEV) penetrates the macular pigment of the eye and causes a breakdown of the retina, leaving the eye more vulnerable to blue light exposure and cell degeneration. <CIT> discloses a light emitting device including: first and second blue light emitting elements having peak wavelengths different from each other. Each peak wavelength being in a wavelength range of <NUM> or more and <NUM> or less. A phosphor layer including a green phosphor which is excited by emission light of the first and second blue light emitting elements, and a red phosphor. <CIT> discloses a semiconductor light emitting device having a first semiconductor light emission element for emitting color light in a first wavelength range, a second semiconductor light emission element for emitting color light in the second wavelength range, a frame electrode for mounting the first and second semiconductor light emission elements, and a package <NUM> for molding them together. <CIT> discloses luminous means comprising at least one optoelectronic semiconductor device which emits electromagnetic radiation during operation, at least one first wavelength and at least one second wavelength. The first wavelength and the second wavelength differ from one another and are below <NUM>. Conversion means are also included which converts the first wavelength at least partly into radiation having a different frequency.

The present invention arose in an endeavor to improve the color rendition of full spectrum light emitting devices comprising photoluminescence conversion materials that generate white light having high color rendering characteristics such as a high CRI Ra and/or high Fidelity index Rf. The present invention also ameliorates problems associated with White LEDs causing damage to the human eye by exposure to HEV as discussed above.

The invention concerns full spectrum white light emitting devices for generating full spectrum white light having a spectral content from blue light to red light that resembles natural sunlight as closely as possible. Full spectrum white light emitting devices in accordance with the invention utilize broadband blue solid-state excitation sources, for example blue LEDs, which generate broadband blue excitation light with a dominant wavelength in a range from <NUM> to <NUM>. In this patent specification "broadband" blue light is used to denote blue light that has a FWHM (Full Width Half Maximum) at least <NUM>, preferably at least <NUM>; or may be used to denote blue light that is composed of a combination of at least two different wavelength blue light emissions in a wavelength range <NUM> to <NUM>. According to the present invention, there is envisaged a full spectrum white light emitting device as defined in Claim <NUM>.

Broadband blue excitation light can be generated using a combination of blue light emissions of two or more different wavelengths; for example, a combination of shorter wavelength blue light in a wavelength range <NUM> to <NUM> and longer wavelength blue light in a wavelength range <NUM> to <NUM>. The different wavelength blue light emissions can be generated in two ways: (i) using multiple individual blue LEDs (narrowband LEDs) of different dominant wavelengths or (ii) individual LEDs (broadband LEDs) that generate multiple blue wavelength emissions using, for example, specially designed multiple different quantum wells in the active region. Thus, a broadband blue solid-state excitation source can be constituted by one
or more narrowband solid-state light sources; such as for example, LEDs or laser diodes, each of which "directly" generates narrowband blue light of different dominant wavelengths in a range from <NUM> to <NUM>. Alternatively, a broadband blue solid-state excitation source also encompasses a broadband blue solid-state light source; for example, a broadband blue LED such as an InGaN/GaN blue LED having an active region that directly generates blue light emissions of multiple different wavelengths, and in accordance with the invention at least three different wavelengths, using different quantum wells in
a multiple-quantum-well (MQW) structure. Broadband blue solid-state excitation sources of the invention are to be contrasted with known white LEDs that utilize narrowband blue LEDs that generate blue light of a single narrowband wavelength having a FWHM in a range <NUM> to <NUM>. The FWHM of broadband blue excitation light of the present invention is at least <NUM>; and the FWHM can for example be in a wavelength range <NUM>
nm to <NUM>, though it can be in ranges <NUM> to <NUM>, <NUM> to <NUM> or <NUM> to <NUM>. Broadband blue solid-state excitation sources of the invention are to be further contrasted with known white LEDs that utilize UV solid-state light sources (UV LEDs) in which the blue excitation light is generated indirectly through a process of photoluminescence conversion of UV light using a blue light emitting (<NUM> - <NUM>) photoluminescence material (phosphor). In other words, broadband blue solid-state excitation sources/white light emitting devices in accordance with the invention do not utilize/include a photoluminescence material to generate excitation light in a range <NUM> - <NUM>.

According to an aspect of the present invention, there is provided a full spectrum white light emitting device comprising: a first photoluminescence material which generates light with a peak emission wavelength in a range <NUM> to <NUM>, and a second photoluminescence material which generates light with a peak emission wavelength in a range <NUM> to <NUM>; and a broadband solid-state excitation source operable to generate excitation light with a dominant wavelength in a range from <NUM> to <NUM> and a FWHM greater than or equal to <NUM>.

According to another example, illustrating but not completely defining the invention, there is envisaged a full spectrum light emitting device that comprises : photoluminescence materials which generate light with a peak emission wavelength in a range <NUM> to <NUM> (green to red region of the visible spectrum) and a broadband blue solid-state excitation source operable to generate broadband blue excitation light with a dominant wavelength in a range from <NUM> to <NUM>, wherein the broadband blue excitation light comprises at least two different wavelength blue light emissions in a wavelength range <NUM> to <NUM>. Full spectrum light emitting devices formed in accordance with the invention and comprising a broadband blue solid-state excitation source which generates broadband blue excitation light (i.e. composed of multiple wavelength blue light emissions) are found to increase the color rendering of white light generated by the device in particular CRI R11 (saturated green) and CRI R12 (saturated blue). Known white LEDs that utilize narrowband (FWHM <NUM> - <NUM>) blue excitation sources and phosphor conversion in the green, yellow and red regions of the visible spectrum exhibit a strong narrow blue peak emission that exceeds that of sunlight and broadband phosphor emissions covering green, yellow and red spectrum for color temperature ranging from <NUM> to <NUM>. Moreover, there is a pronounced trough (valley) in the cyan region of the spectrum (<NUM> to <NUM>) between the blue LED emission and phosphor emission resulting in low values for CRI R11 and CRI R12, particularly for CCT in a range <NUM> to <NUM>. In contrast, in full spectrum light emitting devices in accordance with the invention that utilize broadband blue solid-state excitation sources, the broadband blue excitation light partially fills the cyan spectrum trough thereby significantly improving CRI R11 and CRI R12.

Light emitting devices in accordance with the invention can generate white light that more closely resembles natural sunlight than the known white LEDs. In some embodiments, light emitting devices may be characterized by generating white light with a CRI R1 to CRI R15 (full color spectrum) of greater than or equal to <NUM> and/or a general CRI Ra of greater than or equal to <NUM>. In some embodiments, the light emitting device may be characterized by generating white light with a CRI R1 to CRI R15 of greater than or equal to <NUM> and/or a general CRI Ra of greater than or equal to <NUM>. In embodiments, the light emitting device may be characterized by generating white light with a CRI R12 ("Saturated Blue") of greater than or equal to <NUM>. In embodiments, the light emitting device may be characterized by generating white light with a IEC TM-<NUM> fidelity index Rf of greater than or equal to <NUM>.

In embodiments, the light emitting device may be operable to generate white light with a color temperature in a range from about <NUM> to about <NUM>, a color temperature in a range from about <NUM> to about <NUM>, a color temperature in a range from about <NUM> to about <NUM>, or a color temperature in a range from about <NUM> to about <NUM>.

In some embodiments, there is a difference in wavelength between the at least two blue light emissions of at least <NUM> or at least <NUM>. The broadband blue solid-state excitation source can generate broadband blue excitation light with a FWHM in a range <NUM> to <NUM> and in accordance with the invention, at least <NUM>.

The broadband blue solid-state excitation source may, in illustrative examples not forming part of the invention, comprise two or more solid-state light sources which generate narrowband blue light emissions with a different respective dominant wavelength and the excitation light may comprise the combined light generated by the solid-state light sources. In one such embodiment, a solid-state excitation source comprises a first solid-state light source operable to generate a blue light emission with a first dominant wavelength in a range <NUM> to <NUM> and a second solid-state light source operable to generate blue light emission with a second dominant wavelength in a range from <NUM> to <NUM>. In such an arrangement, the broadband blue excitation light comprises combined light generated by the first and second solid-state light sources. In some embodiments, the first dominant wavelength is in a range from <NUM> to <NUM>; and the second dominant wavelength is in a range from <NUM> to <NUM>.

In other embodiments, the broadband blue solid-state excitation source may comprise an LED having an active region with at least two and in accordance with the invention at least three different quantum wells that each generate a respective one of the at least two different blue light emissions.

In embodiments, the photoluminescence materials can comprise a green to yellow photoluminescence material which generates light with a peak emission wavelength in a range <NUM> to <NUM> and a red photoluminescence material which generates light with a peak emission wavelength in a range <NUM> to <NUM>. Embodiments of the invention can further comprise an orange to red photoluminescence material which generates light with a peak emission wavelength in a range <NUM> to <NUM>.

In embodiments, the light emitting device is characterized by a luminous efficacy (LE) of greater than or equal to <NUM> lm/Wopt or by a luminous efficacy (LE) of greater than or equal to <NUM> lm/Wopt.

Embodiments of the invention find utility in a packaged device where the green to yellow photoluminescence material, red photoluminescence material and optional orange to red photoluminescence material are packaged with the broadband blue solid-state excitation source. In other embodiments, the photoluminescence material can be located remote to the broadband blue solid-state excitation source.

While the invention arose in relation to white light emitting devices for generating full spectrum white light having high color rendering qualities, that is a general CRI Ra of greater than or equal to <NUM>, the invention also finds utility for light emitting devices that generate light with lower CRI Ra, greater than or equal to <NUM>. In such applications, the use of a broadband blue solid-state excitation source can reduce damage to the human retina and/or reduce degeneration of the human macular compared with the known white LEDs that utilize narrow band blue excitation sources. This is because the same blue photon energy is distributed over a greater wavelength range thereby reducing the intensity of the blue peak.

In embodiments, there is envisaged a light emitting device as described herein for use in reducing damage to the human retina, or reducing degeneration of the human macula.

In embodiments, there is encompassed use of a light emitting device as described herein in reducing damage to the human retina, or reducing degeneration of the human macula.

These and other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures, wherein:.

Embodiments of and illustrative examples not forming part of the present invention will now be described in detail with reference to the drawings, which are provided as illustrative examples of the invention so as to enable those skilled in the art to practice the invention. Notably, the figures and examples below are not meant to limit the scope of the present invention to a single embodiment, but other embodiments are possible by way of interchange of some or all of the described or illustrated elements. Moreover, where certain elements of the present invention can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present invention will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the invention. In the present specification, an embodiment showing a singular component should not be considered limiting; rather, the invention is intended to encompass other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or claims to be ascribed an uncommon or special meaning unless explicitly set forth as such.

Throughout this specification, like reference numerals preceded by the figure number are used to denote like features.

Embodiments of the invention concern white light emitting devices that comprise a broadband solid-state excitation source, for example one or more LEDs, that is operable to generate broadband blue excitation light with a dominant wavelength in a range from <NUM> to <NUM>. In this patent specification "broadband" blue light is used to denote blue light that has a FWHM (Full Width Half Maximum) at least <NUM>, in accordance with the invention as claimed at least <NUM>; or may be used to denote blue light that is composed of a combination of at least two, or according to the invention a least three different wavelength blue light emissions, generated by a single InGaN/GaN LED, in a wavelength range <NUM> to <NUM>. More particularly, although not exclusively, embodiments of the invention concern white light emitting devices for generating full spectrum white light that closely resembles sunlight and has high color rendering properties. Embodiments of the invention also concern solid-state white light emitting devices with a broadband blue spectral content that ameliorate problems associated with high intensity of narrow band blue causing damage to the human eye by exposure to blue light (HEV) in the region of <NUM>-<NUM>.

<FIG> illustrate a remote phosphor solid-state full spectrum white light emitting device according to an embodiment in which <FIG> is a partial cross-sectional plan view and <FIG> is a sectional view through A-A. The device <NUM> is configured to generate warm white light with a CCT (Correlated Color Temperature) of between <NUM> and <NUM> and a CRI (Color Rendering Index) of greater than <NUM>. The device can be used alone or comprise a part of a downlight or other lighting arrangement. The device <NUM> comprises a hollow cylindrical body <NUM> composed of a circular disc-shaped base <NUM>, a hollow cylindrical wall portion <NUM> and a detachable annular top <NUM>. To aid in the dissipation of heat, the base <NUM> is preferably fabricated from aluminum, an alloy of aluminum or any material with a high thermal conductivity. The base <NUM> can be attached to the wall portion <NUM> by screws or bolts or by other fasteners or by means of an adhesive.

The device <NUM> further comprises a plurality (five in the example of <FIG>) of broadband blue solid-state excitation sources <NUM> that are mounted in thermal communication with a circular-shaped MCPCB (metal core printed circuit board) <NUM>. Various embodiments of the broadband blue solid-state excitation sources <NUM> are illustrated in <FIG>. To maximize the emission of light, the device <NUM> can further comprise light reflective surfaces <NUM> and <NUM> that respectively cover the face of the MCPCB <NUM> and the inner curved surface of the cylindrical wall <NUM>.

The device <NUM> further comprises a photoluminescence wavelength conversion component <NUM> that is located remotely to the excitation sources <NUM> and operable to absorb a portion of the excitation light generated by the excitation sources <NUM> and convert it to light of a different wavelength by a process of photoluminescence. The emission product of the device <NUM> comprises the combined light generated by the broadband blue excitation sources <NUM> and photoluminescence light generated by the photoluminescence wavelength conversion component <NUM>. The photoluminescence wavelength conversion component may be formed of a light transmissive material (for example, polycarbonate, acrylic material, silicone material, etc.) that incorporates a mixture of a yellow, red and/or green phosphor. Furthermore, in embodiments, the photoluminescence wavelength conversion component may be formed of a light transmissive substrate that is coated with phosphor material(s). The wavelength conversion component <NUM> is positioned remotely to the excitation sources <NUM> and is spatially separated from the excitation sources. In this patent specification, "remotely" and "remote" means in a spaced or separated relationship. Typically, wavelength conversion component and excitation sources are separated by air, while in other embodiments they can be separated by a suitable light transmissive medium, such as for example a light transmissive silicone or epoxy material. The wavelength conversion component <NUM> is configured to completely cover the housing opening such that all light emitted by the lamp passes through the wavelength component <NUM>. As shown, the wavelength conversion component <NUM> can be detachably mounted to the top of the wall portion <NUM> using the top <NUM> enabling the component and emission color of the lamp to be readily changed.

<FIG> is a schematic representation of a broadband blue solid-state excitation source <NUM>, according to an illustrative example falling outside the scope of the invention. The broadband blue solid-state excitation source <NUM> is configured to generate broadband blue excitation light with a dominant wavelength in a range <NUM> to <NUM>, that is, in the blue region of the visible spectrum. In this embodiment, it also has a FWHM in a range <NUM> to <NUM>. In accordance with an embodiment of the invention, the broadband blue solid-state excitation source <NUM> comprises a first solid-state light source <NUM> and a second solid-state light source <NUM>, which in this example are narrowband blue LED chips (e.g. blue-emitting GaN -based LED chips). The first solid-state light source <NUM> generates a blue light emission having a first dominant wavelength λd1 in a range from <NUM> to <NUM> and the second solid-state light source <NUM> generates a blue light emission having a second dominant wavelength λd2 in a range from <NUM> to <NUM>. The first and second solid-state light sources are selected such that the dominant wavelengths of light generated by the sources are different (i.e. λd1 is different to λd2). The combination of light from the first and second solid-state light sources <NUM>/<NUM> constitutes the broadband blue excitation light output <NUM> of the broadband blue solid-state excitation source <NUM> and has a dominant wavelength in a range <NUM> to <NUM> and has a FWHM in a range <NUM> to <NUM>. It will be understood that in other embodiments the solid-state excitation source may comprise a single solid-state light source. In this specification, a single solid-state light source is defined as one or more solid-state light sources each of which generates light with the same (i.e. single/solitary) dominant wavelength and with a FWHM of at least <NUM>.

As indicated in <FIG>, the broadband blue solid-state excitation source <NUM> can comprise a surface mountable device (SMD), such as for example an SMD <NUM> LED package, in which the first and second solid-state light sources are flip-chip bonded on a top face of a substrate <NUM>. Electrical contacts <NUM>, <NUM> can be provided on the bottom face of the substrate <NUM> for operating the excitation source. The first and second solid-state light sources <NUM>, <NUM> can be encapsulated with a light transmissive optical encapsulant <NUM>, such as for example a silicone or epoxy material.

<FIG> is a schematic representation of a broadband blue solid-state excitation source <NUM>, according to an embodiment of the invention. The solid-state excitation source <NUM> is configured to generate excitation light with a dominant wavelength in a range <NUM> to <NUM>, that is, in the blue region of the visible spectrum. In this embodiment, it also has a FWHM in a range <NUM> to <NUM>. In accordance with an embodiment of the invention, the solid-state excitation source <NUM> comprises a broadband solid-state light source <NUM>, which in this example is a single broadband LED such as for example an InGaN/GaN blue LED having an active region with multiple-quantum-wells (MQWs), as disclosed in <NPL>". The broadband solid-state light source <NUM> generates broadband blue light comprising multiple overlapping blue light emissions of at least three peak wavelengths in a range from <NUM> to <NUM>. Thus, the single solid-state light source <NUM> generates light with a single/solitary dominant wavelength and with a FWHM of at least <NUM>.

As indicated in <FIG>, the solid-state excitation source <NUM> can comprise a surface mountable device (SMD), such as for example an SMD <NUM> LED package, in which the solid-state light source is flip-chip bonded on a top face of a substrate <NUM>. Electrical contacts <NUM>, <NUM> can be provided on the bottom face of the substrate <NUM> for operating the excitation source. The solid-state light source <NUM> can be encapsulated with a light transmissive optical encapsulant <NUM>, such as for example a silicone or epoxy material.

<FIG> is a schematic cross-sectional representation of a packaged full spectrum white light emitting device 310a, according to an illustrative example falling outside the scope of the invention. The device 310a is configured to generate warm white light with a CCT (Correlated Color Temperature) of in a range <NUM> to <NUM> and a General CRI (Color Rendering Index) CRI (Ra) of <NUM> and higher.

In accordance with embodiments of the invention, the device 310a comprises a broadband blue solid-state excitation source constituted by first and second solid-state light sources <NUM>, <NUM>, for example blue-emitting GaN (gallium nitride)-based LED chips, that are housed within a package <NUM>. In a similar/same manner as described above, the first solid-state light source <NUM> can generate a blue light emission having a first dominant wavelength λd1 in a range from <NUM> to <NUM> and the second solid-state light source <NUM> can generate a blue light emission having a second dominant wavelength λd2 in a range from <NUM> to <NUM>. The dominant wavelength λd1 of the first solid-state light source is different from the dominant wavelength λd2 of the second solid-state light source. The package, which can for example comprise Surface Mountable Device (SMD) such as an SMD <NUM> LED package, comprising upper portion <NUM> and base portion <NUM>. The upper body part <NUM> defines a recess <NUM> which is configured to receive the solid-state light sources <NUM>, <NUM>. The package <NUM> can further comprise electrical connectors <NUM> and <NUM> on an exterior face of the base of the package <NUM>. The electrical connectors <NUM>, <NUM> can be electrically connected to electrode contact pads <NUM>, <NUM> and <NUM> on the floor of the recess <NUM>. Using adhesive or solder, the solid-state light sources (LED chips) <NUM>, <NUM> can be mounted to a thermally conductive pad <NUM> located on the floor of the recess <NUM>. The LED chip's electrode pads can be electrically connected to corresponding electrode contact pads <NUM>, <NUM> and <NUM> on the floor of the package <NUM> using bond wires <NUM>. Alternatively, the LED chips can be flip-chip mounted in and electrically connected to the package. The recess <NUM> is filled with a light transmissive optical encapsulant <NUM>, typically an optically clear silicone, which is loaded with a mixture of photoluminescence materials such that the exposed surfaces of the LED chips <NUM>, <NUM> are covered by the photoluminescence/silicone material mixture. To enhance the emission brightness of the device the walls of the recess <NUM> can be inclined and have a light reflective surface. Of course, it will be understood that in other embodiments the one or more solid-state light sources (LED chips <NUM>, <NUM>) each generate light with the same (i.e. single/solitary) dominant wavelength and with a FWHM of at least <NUM>.

<FIG> is another embodiment. It is similar to <FIG> except that the first and second narrowband solid-state light sources are replaced by two broadband blue LEDs 341a/341b having an active region with multiple-quantum-wells. Typically, the first and second broadband blue solid-state light sources 341a/341b each generate broadband blue excitation light having dominant wavelengths λd which are the same.

<FIG> illustrate a Chip On Board (COB) packaged full spectrum white light emitting device <NUM> according to an embodiment in which <FIG> is a plan view and <FIG> is a sectional view through B-B. The device <NUM> is configured to generate warm white light with a CCT (Correlated Color Temperature) of between <NUM> and <NUM> and a CRI (Color Rendering Index) of greater than <NUM>.

The device <NUM> comprises a plurality (twelve in the example of <FIG>) broadband blue solid-state excitation sources <NUM>, for example broadband blue-emitting GaN (gallium nitride)-based LED flip-chip dies, mounted in thermal communication with a square-shaped MCPCB <NUM>.

As indicated in <FIG>, the excitation sources <NUM> can be configured as a generally circular array. The solid-state excitation sources (broad-band LED dies) <NUM> can each generate excitation light having a dominant wavelength λd in a range from <NUM> to <NUM>. In this embodiment, theyhave a FWHM (Full Width Half Maximum) in a range <NUM> to <NUM>. Electrical contacts <NUM>, <NUM> can be provided on the top face of the MCPCB <NUM> for operating the white light emitting device <NUM>. As shown, the broad-band LED flip-chip dies <NUM> are encapsulated with a light transmissive optical encapsulant <NUM>, such as for example a silicone or epoxy material, which is loaded with a mixture of photoluminescence materials such that the exposed surfaces of the LED dies <NUM> are covered by the photoluminescence/silicone material mixture. As shown, the light transmissive encapsulant/photluminescence material mixture <NUM> can be contained within an annular-shaped wall <NUM>. Of course, it will be understood that in other embodiments, the arrangement depicted in <FIG> could comprise, in embodiments not forming part of the claimed invention, solid-state excitation sources <NUM> constituted by two or more LEDs rather than a single broadband InGaN/GaN blue LED having an active region with multiple-quantum-wells.

In this patent specification, a green to yellow photoluminescence material refers to a material which generates light having a peak emission wavelength (λpe) in a range ~<NUM> to ~<NUM>, that is in the green to yellow region of the visible spectrum. Preferably, the green to yellow photoluminescence material has a broad emission characteristic and preferably has a FWHM (Full Width Half Maximum) of ~<NUM> or wider. The green to yellow photoluminescence material can comprise any photoluminescence material, such as for example, garnet-based inorganic phosphor materials, silicate phosphor materials and oxynitride phosphor materials. Examples of suitable green to yellow phosphors are given in Table <NUM>.

In some embodiments, the green to yellow photoluminescence materials comprises a cerium-activated yttrium aluminum garnet phosphor of general composition Y<NUM>(Al,Ga)<NUM>O<NUM>:Ce (YAG) such as for example a YAG series phosphor from Intematix Corporation, Fremont California, USA which have a peak emission wavelength of in a range <NUM> to <NUM> and a FWHM of ~<NUM>. In this patent specification, the notation YAG# represents the phosphor type - YAG - based phosphors - followed by the peak emission wavelength in nanometers (#). For example, YAG535 denotes a YAG phosphor with a peak emission wavelength of <NUM>. The green to yellow photoluminescence material may comprise a cerium-activated yttrium aluminum garnet phosphor of general composition (Y,Ba)<NUM>(Al,Ga)<NUM>O<NUM>:Ce (YAG) such as for example a GNYAG series phosphor from Intematix Corporation, Fremont California, USA. In some embodiments, the green photoluminescence material can comprise an aluminate (LuAG) phosphor of general composition Lu<NUM>Al<NUM>O<NUM>:Ce (GAL). Examples of such phosphors include for example the GAL series of phosphor from Intematix Corporation, Fremont California, USA which have a peak emission wavelength of <NUM> to <NUM> and a FWHM of ~<NUM>. In this patent specification, the notation GAL# represents the phosphor type (GAL) - LuAG - based phosphors - followed by the peak emission wavelength in nanometers (#). For example, GAL520 denotes a GAL phosphor with a peak emission wavelength of <NUM>.

Examples of green to yellow silicate phosphors include europium activated ortho-silicate phosphors of general composition (Ba, Sr)<NUM>SiO<NUM>: Eu such as for example G, EG, Y and EY series of phosphors from Intematix Corporation, Fremont California, USA which have a peak emission wavelength in a range <NUM> to <NUM> and a FWHM of ~<NUM> to ~<NUM>. In some embodiments, the green to yellow phosphor can comprise a green-emitting oxynitride phosphor as taught in <CIT> entitled "Green-Emitting (Oxy) Nitride-Based Phosphors and Light Emitting Devices Using the Same". Such a green-emitting oxynitride (ON) phosphor can have a general composition Eu<NUM>+:M<NUM>+Si<NUM>AlOxN(<NUM>-2x/<NUM>) where <NUM> ≤ x ≤ <NUM> and M<NUM>+ is one or more divalent metal selected from the group consisting of Mg, Ca, Sr, Ba, and Zn. In this patent specification, the notation ON# represents the phosphor type (oxynitride) followed by the peak emission wavelength (λpe) in nanometers (#). For example, ON495 denotes a green oxynitride phosphor with a peak emission wavelength of <NUM>.

The orange to red photoluminescence material can comprise any orange to red photoluminescence material, typically a phosphor, that is excitable by blue light and operable to emit light with a peak emission wavelength λpe in a range about <NUM> to about <NUM> and can include, for example, a europium activated silicon nitride-based phosphor, α-SiAlON, Group IIA/IIB selenide sulfide-based phosphor or silicate-based phosphors. Examples of orange to red phosphors are given in Table <NUM>.

In some embodiments, the europium activated silicon nitride-based phosphor comprises a Calcium Aluminum Silicon Nitride phosphor (CASN) of general formula CaAlSiN<NUM>:Eu<NUM>+. The CASN phosphor can be doped with other elements such as strontium (Sr), general formula (Sr,Ca)AlSiN<NUM>:Eu<NUM>+. In this patent specification, the notation CASN# represents the phosphor type (CASN) followed by the peak emission wavelength (λpe) in nanometers (#). For example, CASN615 denotes an orange to red CASN phosphor with a peak emission wavelength of <NUM>.

In one embodiment, the orange to red phosphor can comprise an orange to red-emitting phosphor as taught in <CIT> entitled "Red-Emitting Nitride-Based Calcium-Stabilized Phosphors". Such a red emitting phosphor comprises a nitride-based composition represented by the chemical formula MaSrbSicAldNeEuf, wherein: M is Ca, and <NUM> ≤ a ≤ <NUM>; <NUM> < b < <NUM>; <NUM> ≤ c ≤ <NUM>; <NUM> ≤ d ≤ <NUM>; <NUM> < e < <NUM>; and <NUM> < f < <NUM>; wherein a+b+f ><NUM>+d/v and v is the valence of M.

Alternatively, the orange to red phosphor can comprise an orange to red emitting nitride-based phosphor as taught in <CIT> entitled "Red-Emitting Nitride-Based Phosphors". Such a red emitting phosphor comprising a nitride-based composition represented by the chemical formula M(x/v)M'<NUM>Si<NUM>-xAlxN<NUM> :RE, wherein: M is at least one monovalent, divalent or trivalent metal with valence v; M' is at least one of Mg, Ca, Sr, Ba, and Zn; and RE is at least one of Eu, Ce, Tb, Pr, and Mn; wherein x satisfies <NUM>≤ x<<NUM>, and wherein said red-emitting phosphor has the general crystalline structure of M'<NUM>Si<NUM>N<NUM>:RE, Al substitutes for Si within said general crystalline structure, and M is located within said general crystalline structure substantially at the interstitial sites. An example of one such a phosphor is XR610 red nitride phosphor from Intematix Corporation, Fremont California, USA which has a peak emission wavelength of <NUM>.

Orange to red phosphors can also include Group IIA/IIB selenide sulfide-based phosphors. A first example of a Group IIA/IIB selenide sulfide-based phosphor material has a composition MSe<NUM>-xSx:Eu, wherein M is at least one of Mg, Ca, Sr, Ba and Zn and <NUM> < x < <NUM>. A particular example of this phosphor material is CSS phosphor (CaSe<NUM>-xSx:Eu). Details of CSS phosphors are provided in co-pending United States patent application Publication Number <CIT>. The CSS orange to red phosphors described in United States patent publication <CIT> can be used in the present invention. The emission peak wavelength of the CSS phosphor can be tuned from <NUM> to <NUM> by altering the S/Se ratio in the composition and exhibits a narrow-band red emission spectrum with FWHM in the range ~ <NUM> to ~ <NUM> (longer peak emission wavelength typically has a larger FWHM value). In this patent specification, the notation CSS# represents the phosphor type (CSS) followed by the peak emission wavelength in nanometers (#). For example, CSS615 denotes a CSS phosphor with a peak emission wavelength of <NUM>. To improve reliability, the CSS phosphor particles can be coated with one or more oxides, for example: aluminum oxide (Al<NUM>O<NUM>), silicon oxide (SiO<NUM>), titanium oxide (TiO<NUM>), zinc oxide (ZnO), magnesium oxide (MgO), zirconium oxide (ZrO<NUM>), boron oxide (B<NUM>O<NUM>) or chromium oxide (CrO). Alternatively, and/or in addition, the narrow-band red phosphor particles may be coated with one or more fluorides, for example: calcium fluoride (CaF<NUM>), magnesium fluoride (MgF<NUM>), zinc fluoride (ZnF<NUM>), aluminum fluoride (AlF<NUM>) or titanium fluoride (TiF<NUM>). The coatings may be a single layer, or multiple layers with combinations of the aforesaid coatings. The combination coatings may be coatings with an abrupt transition between the first and second materials, or may be coatings in which there is a gradual/smooth transition from the first material to the second material thus forming a zone with mixed composition that varies through the thickness of the coating.

In some embodiments, the orange to red phosphor can comprise an orange-emitting silicate-based phosphor as taught in United States Patent <CIT> entitled "Silicate-Based Orange Phosphors". Such an orange-emitting silicate-based phosphor can have a general composition (Sr<NUM>-xMx)yEuzSiO<NUM> where <NUM> < x ≤ <NUM>, <NUM> ≤ y ≤ <NUM>, <NUM> ≤ z ≤ <NUM> and M is one or more divalent metal selected from the group consisting of Ba, Mg, Ca, and Zn. In this patent specification, the notation O# represents the phosphor type (orange silicate) followed by the peak emission wavelength (λpe) in nanometers (#). For example, O600 denotes an orange silicate phosphor with a peak emission wavelength of <NUM>.

As described above, the broadband blue solid-state excitation source can comprise solid-state light sources (for example LEDs) of two or, in accordance with the invention three or more different dominant wavelengths.

<FIG> is a measured emission spectrum, normalized intensity (a. ) versus wavelength (nm), for a <NUM> narrowband LED (Prior art) and <FIG> is a measured emission spectrum, normalized intensity (a. ) versus wavelength (nm), for a broadband blue solid-state excitation source comprising a combination of two LEDs with dominant wavelengths λd1 = <NUM> and λd2 = <NUM>. It can be seen that both emission spectra (FIFG. 5a and 5b) exhibit a single maximum peak <NUM> and <NUM> respectively. Comparing the figures visually illustrates the increase in FWHM when using a combination of LEDs with two different dominant wavelengths compared with an LED of a single dominant wavelength. More specifically, for a broadband blue solid-state excitation source in accordance with the invention comprising a combination of LEDs with two different dominant wavelengths (λd1= <NUM> and λd2 = <NUM>), the dominant wavelength of the excitation light generated by the source is <NUM> with a FWHM of about <NUM>. For comparison, a solitary narrowband LED with substantially the same dominant wavelength (<NUM>) generates light with a FWHM of only <NUM>. As described below, it is the increase in FWHM of the excitation light (i.e. <NUM> to <NUM>) that advantageously gives rise to the enhanced optical performance of light emitting devices in accordance with the invention.

In accordance with the invention, the broadband blue solid-state excitation source comprises solid-state light sources (for example LEDs) with three or more different dominant wavelengths. <FIG> shows measured emission spectra, normalized intensity (a. ) versus wavelength (nm), for broadband blue excitation sources in accordance with the invention comprising (i) a combination of blue LEDs with two different dominant wavelengths λd1 = <NUM> and λd2 = <NUM> (solid line) and (ii) a combination of blue LEDs with three different dominant wavelengths λd1 = <NUM>, λd2 = <NUM> and λd3 = <NUM> (dotted line). <FIG> visually indicates the effect of using a combination of LEDs with three different dominant wavelengths compared with an excitation source comprising a combination of LEDs with two different dominant wavelengths. For a solid-state excitation source comprising a combination of LEDs with two different dominant wavelengths (λd1 = <NUM> and λd2 = <NUM>), the dominant wavelength of the excitation light generated by the source is <NUM> with a FWHM of <NUM>. However, as will be noted in <FIG>, the excitation source comprising LEDs with two different dominant wavelengths generates excitation light whose spectrum exhibits two distinct peaks 682a, 682b. The FWHM of the excitation source is defined as the wavelength range corresponding to half of the maximum peak. For comparison, an excitation source comprising a combination of LEDs with three different dominant wavelengths generates excitation light with a dominant wavelength of <NUM> and has a FWHM of <NUM>. However, as will be noted in <FIG>, the excitation source comprising LEDs with three different dominant wavelengths generates excitation light whose spectrum exhibits a single peak <NUM>. Exhibiting a single peak compared with a dual peak can be attributed to the LEDs having a smaller range in wavelength; that is <NUM> - <NUM> compared with <NUM> - <NUM>.

As described above, and in accordance with the invention, the broadband blue solid-state excitation source comprises one or more broadband blue solid-state light sources (for example MQW LED chips). <FIG> shows measured emission spectrum, normalized intensity (a. ) versus wavelength (nm) for a broadband blue excitation source comprising a broadband MQW LED. The MQW LED comprises nine quantum wells and generates light with a FWHM <NUM>, thus falling within the FWHM range of <NUM> to <NUM> in accordance with the invention. As depicted in <FIG>, the spectrum exhibits three peaks 782a, 782b and 782c which is attributable to the multiple different quantum wells generating three different peak wavelengths (blue light emissions).

The remote phosphor test method involves measuring total light emission of a remote phosphor white light emitting device (<FIG>) in an integrating sphere.

The photoluminescence wavelength conversion component (<NUM> - <FIG>) comprises a ϕ <NUM> diameter circular borosilicate glass disc. The phosphor materials are mixed with an optical encapsulant OE6370 from Dow Corning (silicone resin) and the resulting mixture applied as a layer to one face of the glass disc and cured.

In this specification, the following nomenclature is used to denote remote phosphor light emitting devices: Com. # denotes a comparative light emitting device in which each excitation source comprises one or more solid-state light sources of a single dominant wavelength and Dev. # denotes a light emitting device in accordance with an embodiment in which each excitation source comprises solid-state light sources of two different dominant wavelengths. Comparative light emitting devices (Com. #) comprise eight solid-state excitation sources each of which comprises a <NUM>, <NUM> packaged LED chip. Therefore, Com. # comprises a total of eight LED chips. Light emitting devices in accordance with the embodiment (Dev. #) comprise six solid-state excitation sources (<NUM> - <FIG>) each of which comprises a <NUM> package containing two LED chips of dominant wavelength λd1 = <NUM> and λd2 = <NUM>. Therefore, Dev. # comprises a total of twelve LED chips.

Table <NUM> tabulates phosphor compositions for nominal <NUM> light emitting devices for a comparative device denoted Com. <NUM> and a remote phosphor full spectrum white light emitting device in accordance with the embodiment, denoted Dev.

As can be seen from Table <NUM>, in terms of phosphor composition: Com. <NUM> and Dev. <NUM> each comprise <NUM> wt% ON495 (Eu<NUM>+:M<NUM>+Si<NUM>AlOxN(<NUM>-2x/<NUM>) - λpe=<NUM>), <NUM> wt% GAL520 (Lu<NUM>-x(Al<NUM>-yGay)<NUM>O<NUM>:Cex - λpe=<NUM>), <NUM> wt% O600 ((Sr<NUM>-xMx)yEuzSiO<NUM> - λpe=<NUM>) and <NUM> wt% CASN670 (Ca<NUM>-xSrxAlSiN<NUM>:Eu - λpe=<NUM>). As described above, Com. <NUM> comprises eight solid-state excitation sources each of which comprises a <NUM>, <NUM> packaged LED chip, while Dev. <NUM> comprises six broadband blue solid-state excitation sources each of which comprises a <NUM> package containing two LED chips of dominant wavelength λd1 = <NUM> and λd2 = <NUM>.

Tables <NUM>, <NUM> and <NUM> tabulates measured optical test data for light emitting devices Com. <NUM> and Dev. <NUM> and illustrate the effect on light emitting device optical performance of using a broadband blue solid-state excitation source in accordance with the embodiment comprising a combination of two or more solid-state LEDs of different dominant wavelengths (λd1 = <NUM> and λd2 = <NUM>) compared with using a solid-state excitation source comprising solid-state LEDs of a single dominant wavelength (λd = <NUM>). It is to be noted from these tables that device Dev. <NUM> produces white light in which (i) each of CRI R1 to CRI R15 is <NUM> or higher, (ii) there is a substantial increase in CRI R11 ("Saturated Green") - <NUM> compared with <NUM>, (iii) there is a substantial increase in CRI R12 ("Saturated Blue") - <NUM> compared with <NUM>, (iv) there is a substantial increase in general color rendering index CRI Ra - <NUM> compared with <NUM>, (v) there is a substantial increase in color rendering index CRI Rall (average of R1 to R15) - <NUM> compared with <NUM>, (vi) there is a substantial increase in IEC TM-<NUM> fidelity index Rf - <NUM> compared with <NUM>. Further, it is to be noted that while the invention results in a substantial increase in the quality (color rendering) of light, there is only a small reduction <NUM>% in luminous efficacy LE, and Dev. <NUM> has a high luminous efficacy LE of <NUM> lm/Wopt.

<FIG> shows normalized intensity versus wavelength (nm) for (i) Dev. <NUM> (thick solid line), (ii) Com. <NUM> (dashed line), (iii) Plankian spectrum (thin solid line) for a CCT that is the same as that of Dev. <NUM> (<NUM>), and (iv) Plankian spectrum (dotted line) for a CCT that is the same as that of Com. <NUM> (<NUM>). To make a meaningful comparison of the spectra, each spectra has been normalized such each has a CIE <NUM> XYZ relative luminance Y=<NUM>. The data are normalized using the CIE <NUM> luminosity function y(λ) of a standard observer which takes account of the photopic response of an observer. The Plankian spectrum (curve) or black-body spectra in <FIG> represents the spectrum for a General CRI Ra equal to <NUM> for a given color temperature (CCT). Accordingly, for a white light emitting device of a given color temperature to have the highest color rendering possible, its emission spectrum should match as closely as possible the black-body spectrum of the same color temperature.

Referring to <FIG>, it will be noted that the most pronounced effect on the emission spectral energy content - of the device in accordance with the embodiment (i.e. broadband blue excitation source comprising two solid-state light sources with different dominant wavelengths) compared with the comparative device (i.e. excitation source comprising solid-state light sources with a single dominant wavelength) are: (i) a reduction in the intensity of the blue emission peak <NUM> and (ii) a decrease in trough (valley) <NUM> in the cyan region of the spectrum at about <NUM>. As can be seen from the figure, the reduction of the blue emission peak <NUM> of Dev. <NUM> (compared with peak <NUM> of Com. <NUM>) and decrease in trough <NUM> results in the emission spectrum more closely resembling the Plankian spectrum, that is more closely resembling natural sunlight. It is believed that this change in spectral energy content resulting from the use of a broadband blue excitation source, in this embodiment comprising two solid-state light sources, with different dominant wavelengths (blue light emissions) partially fills the trough in the cyan region of the spectrum accounts for the superior color rendering properties of the devices of the invention; in particular, the increase in CIE CRI R11 and CRI R12, General CRI Ra and IEC TM-<NUM> fidelity index Rf.

A further advantage of the present invention is that white light emitting devices according to the invention can reduce or possibly prevent the likelihood of damage to the human retina and macula by reducing High Energy Visible (HEV) blue light in the wavelength region <NUM> - <NUM>. The blue photon energy (area under the peak) for the blue peaks <NUM> (Com. <NUM>) and <NUM> (Dev. <NUM>) are substantially the same. However, in the case of the peak <NUM> this energy is distributed over a greater wavelength range thereby reducing the intensity of the blue peak compared with the peak <NUM>. Since the white light emitting device of the present invention exhibits a reduction in the blue emission peak (i.e. HEV), the likelihood of damage being caused to the human retina and degeneration of the human macula is reduced or prevented.

Table <NUM> tabulates phosphor compositions for nominal <NUM> light emitting devices for a comparative device denoted Com. <NUM> and a remote phosphor light emitting device in accordance with the embodiment, denoted Dev.

As can be seen from Table <NUM>, in terms of phosphor composition: Com. <NUM> comprises <NUM> wt% GAL520 (Lu<NUM>-x(Al<NUM>-yGay)<NUM>O<NUM>:Cex - λpe=<NUM>), <NUM> wt% CASN628 (Ca<NUM>-xSrxAlSiN<NUM>:Eu - λpe=<NUM>) and <NUM> wt% CASN670 (Ca<NUM>-xSrxAlSiN<NUM>:Eu λpe=<NUM>) while Dev. <NUM> comprises <NUM> wt% GAL520, <NUM> wt% CASN628 and <NUM> wt% CASN670. As described above, Com. <NUM> comprises eight solid-state excitation sources each of which comprises a <NUM>, <NUM> packaged LED chip, while Dev. <NUM> comprises six broadband blue solid-state excitation sources each of which comprises a <NUM> package containing two LED chips of dominant wavelength λd1 = <NUM> and λd2 = <NUM>.

Tables <NUM>, <NUM> and <NUM> tabulates measured optical test data for light emitting devices Com. <NUM> and Dev. <NUM> and illustrate the effect on light emitting device optical performance of using a broadband blue excitation source in accordance with the embodiment comprising a combination of two or more solid-state LEDs of different dominant wavelengths (λd1 = <NUM> and λd2 = <NUM>) compared with using an excitation comprising solid-state LEDs of a single dominant wavelengths (λd = <NUM>). It is to be noted from these tables that device Dev. <NUM> produces white light in which (i) each of CRI R1 to CRI R15 is <NUM> or higher having (ii) there is an increase in CRI R11 ("Saturated Green") - <NUM> compared with <NUM> (ii) there is a substantial increase in CRI R12 ("Saturated Blue") - <NUM> compared with <NUM> and (ii) a substantial increase in IEC TM-<NUM> fidelity index Rf - <NUM> compared with <NUM>. Further it is to be noted, that while the invention results in a substantial increase in the quality (color rendering) of light, there is no reduction in luminous efficacy LE - rather, there is an increase of <NUM>% in luminous efficacy LE and Dev. <NUM> has a high luminous efficacy (LE) of <NUM> lm/Wopt.

<FIG> shows normalized intensity versus wavelength (nm) for (i) Dev. <NUM> (thick solid line), (ii) Com. <NUM> (dashed line), (iii) Plankian spectrum (thin solid line) for a CCT that is the same as that of Dev. <NUM> (<NUM>), and (iv) Plankian spectrum (dotted line) for a CCT that is the same as that of Com. <NUM> (<NUM>). Referring to <FIG>, it will be noted that the most pronounced effect on the emission spectra - spectral energy content - of the device in accordance with the embodiment (i.e. broadband blue solid-state excitation source comprising two solid-state light sources with different dominant wavelengths) compared with the comparative device (i.e. excitation source comprising solid-state light sources with a single dominant wavelength) are: (i) a reduction in the intensity of the blue emission peak <NUM> and (ii) a decrease in trough <NUM> in the cyan region of the spectrum at about <NUM>. As can be seen from the figure, the reduction of the blue emission peak <NUM> of Dev. <NUM> (compared with peak <NUM> of Com. <NUM>) and decrease in trough <NUM> results in the emission spectrum more closely resembling the Plankian spectrum, that is more closely resembling natural sunlight. It is believed that this change in spectral energy content resulting from the use of a broadband blue excitation source, in this embodiment comprising two solid-state light sources, with different dominant wavelengths (blue light emissions) partially fills the trough in the cyan region of the spectrum accounts for the superior color rendering properties of the devices of the invention; in particular, the increase in CRI R12, General CRI Ra and IEC TM-<NUM> fidelity index Rf.

As can be seen from Table <NUM>, in terms of phosphor composition: Com. <NUM> comprises <NUM> wt% GAL520, <NUM> wt% CASN628 and <NUM> wt% CASN670 while Dev. <NUM> comprises <NUM> wt% GAL520, <NUM> wt% CASN628 and <NUM> wt% CASN670. As described above, Com. <NUM> comprises eight solid-state excitation sources each of which comprises a <NUM>, <NUM> packaged LED chip, while Dev. <NUM> comprises six broadband blue solid-state excitation sources each of which comprises a <NUM> package containing two LED chips of dominant wavelength λd1 = <NUM> and λd2 = <NUM>.

Tables <NUM>, <NUM> and <NUM> tabulates measured optical test data for light emitting devices Com. <NUM> and Dev. <NUM> and illustrate the effect on light emitting device optical performance of using a broadband blue excitation source comprising a combination of two or more solid-state LEDs of different dominant wavelengths (λd1 = <NUM> and λd2 = <NUM>) compared with using an excitation comprising solid-state LEDs of a single dominant wavelengths (λd = <NUM>). It is to be noted from these tables that device Dev. <NUM> produces white light in which (i) each of CRIR1 to CRI R15 is <NUM> or higher, (ii) there is a substantial increase in (i) CRI R12 ("Saturated Blue") - <NUM> compared with <NUM> and (iii) there is a substantial increase in IEC TM-<NUM> fidelity index Rf - <NUM> compared with <NUM>. Further, it is to be noted that while the invention results in a substantial increase in the quality (color rendering) of light, there is only a very small reduction (<NUM>%) in luminous efficacy LE and the device has a high luminous efficacy of <NUM> lm/Wopt.

<FIG> shows normalized intensity versus wavelength (nm) for (i) Dev. <NUM> (thick solid line), (ii) Com. <NUM> (dashed line), (iii) Plankian spectrum (thin solid line) for a CCT that is the same as that of Dev. <NUM> (<NUM>), and (iv) Plankian spectrum (dotted line) for a CCT that is the same as that of Com. <NUM> (<NUM>). Referring to <FIG>, it will be noted that the most pronounced effect on the emission spectra - spectral energy content - of the device in accordance with the embodiment (i.e. broadband blue excitation source comprising two solid-state light sources with different dominant wavelengths) compared with the comparative device (i.e. excitation source comprising solid-state light sources with a single dominant wavelength) are: (i) a reduction in blue emission peak <NUM> and (ii) a decrease in trough <NUM> in the cyan region of the spectrum at about <NUM>. As can be seen from the figure, the reduction of the blue emission peak <NUM> of Dev. <NUM> (compared with peak <NUM> of Com. <NUM>) and decrease in trough <NUM> results in the emission spectrum more closely resembling the Plankian spectrum. It is believed that this change in spectral energy content resulting from the use of a broadband blue excitation source, in this embodiment comprising two solid-state light sources, with different dominant wavelengths accounts for the superior color rendering properties of the devices of the invention; in particular, the increase in CRI R12, and IEC TM-<NUM> fidelity index Rf.

As with other embodiments of the invention, a further advantage of full spectrum white light of the invention is that they can reduce or possibly prevent the likelihood of damage to the human retina and macula by reducing High Energy Visible (HEV) blue light in the wavelength region <NUM> - <NUM>. The blue photon energy (area under the peak) for the blue peaks <NUM> (Com. <NUM>) and <NUM> (Dev. <NUM>) are substantially the same. However, in the case of the peak <NUM> this energy is distributed over a greater wavelength range thereby reducing the intensity of the blue peak compared with the peak <NUM>. Since the white light emitting device of the present invention exhibits a reduction in the blue emission peak (i.e. HEV), the likelihood of damage being caused to the human retina and degeneration of the human macula is reduced or prevented.

The packaged test method involves measuring total light emission of a packaged white light emitting device (<FIG>) in an integrating sphere.

Packaged full spectrum white light emitting devices in accordance with the invention (Dev. #) each comprise a <NUM> (<NUM> x <NUM>) SMD package containing solid-state light sources of two or, according to the invention three different dominant wavelengths. Light emitting devices in accordance with the embodiment Dev. <NUM> comprise a <NUM> SMD package containing two <NUM> (11mil by <NUM>) LED chips of dominant wavelength λd1 = <NUM> and λd2 = <NUM> while Dev. <NUM> comprises a <NUM> SMD package containing three <NUM> LED chips of dominant wavelength λd1 = <NUM>, λd2 = <NUM> and λd3 = <NUM>.

Table <NUM> tabulates phosphor compositions for nominal <NUM> light emitting devices for packaged white light emitting devices in accordance with the embodiment, denoted Dev. <NUM> and Dev.

As can be seen from Table <NUM>, in terms of phosphor composition: Dev. <NUM> comprises <NUM> wt% GAL520 (Lu<NUM>-x(Al<NUM>-yGay)<NUM>O<NUM>:Cex - λpe=<NUM>), <NUM> wt% GAL484 (λpe=<NUM>), and <NUM> wt% CASN650 (Ca<NUM>-xSrxAlSiN<NUM>:Eu - λpe=<NUM>) and Dev. <NUM> comprises <NUM> wt% GAL520, <NUM> wt% GAL484, <NUM> wt% CASN628 (Ca<NUM>-xSrxAlSiN<NUM>:Eu - λpe=<NUM>) and <NUM> wt% CASN650. As described above, Dev. <NUM> comprises two solid-state light sources (LEDs) with a respective dominant wavelength λd1 = <NUM> and λd2 = <NUM>, while Dev. <NUM> comprises three LED with a respective dominant wavelength λd1 = <NUM>, λd2 = <NUM> and λd3 = <NUM>.

Tables <NUM>, <NUM> and <NUM> tabulates measured optical test data for packaged light emitting devices Dev. <NUM> and Dev. These data illustrate that full spectrum white light emitting devices that provide utility can be constituted by broadband blue solid-state excitation source comprising a combination of two solid-state light sources (LEDs) of different dominant wavelengths (λd1 = <NUM> and λd2 = <NUM>) or a combination of three solid-state LEDs of different dominant wavelength (λd1 = <NUM>, λd2 = <NUM> and λd3 = <NUM>).

It is to be noted from these tables that device Dev. <NUM> has a high luminous efficacy LE of <NUM> lm/Wopt and produces white light: (i) in which each of CRI R1 to CRI R15 are approximately <NUM> or higher, (ii) having a high CRI R11 ("Saturated Green") of <NUM>, (iii) having a high CRI R12 ("Saturated Blue") of <NUM>, (iv) having a high general color rendering index CRI Ra of <NUM>, (v) having a high color rendering index CRI Rall (average of R1 to R15) of <NUM>, and (vi) having a high IEC TM-<NUM> fidelity index Rf of <NUM>.

It is to be noted from these tables that device Dev. <NUM> has a high luminous efficacy LE of <NUM> lm/Wopt and produces white light: (i) in which with the exception of CRI R12 each of CRI R1 to CRI R15 is <NUM> or higher, (ii) having a high CRI R11 ("Saturated Green") of <NUM>, (iii) having a high general color rendering index CRI Ra of <NUM>, (iv) having a high color rendering index CRI Rall (average of CRI R1 to R15) of <NUM>, and (v) having a high IEC TM-<NUM> fidelity index Rf of <NUM>.

<FIG> shows normalized intensity versus wavelength (nm) for (i) Dev. <NUM> (thick solid line) and (ii) Plankian spectrum (thin solid line) for a CCT that is the same as that of Dev. <NUM> (<NUM>). As can be seen from the figure, the spectrum (thick solid line) closely resembles the Plankian spectrum and exhibits two pronounced peaks 1182a and 1182b separated by a deep trough <NUM> at about <NUM> the combination of which corresponds to the broadband blue excitation light and a trough <NUM> in the cyan region (<NUM>) of the spectrum. It is believed that the lower value of CRI R12 of <NUM> compared with the values of CRI R1 to R11 and R13 to R15 (Tables <NUM> and <NUM>) results from the trough <NUM> which drops below the Plankian spectrum and the trough due to the difference in the LED dominant wavelengths being too high (λd1 = <NUM> and λd2 = <NUM> - Δ λd = <NUM>). The value of CRI R12 can therefore be increased to <NUM> or higher by reducing the difference in dominant wavelength of the LEDs. <FIG> shows normalized intensity versus wavelength (nm) for (i) Dev. <NUM> (thick solid line) and (ii) Plankian spectrum (thin solid line) for a CCT that is the same as that of Dev. <NUM> (<NUM>). Each spectrum has been normalized such each has a CIE <NUM> XYZ relative luminance Y=<NUM>. As can be seen from the figure, the spectrum (thick solid line) exhibits a peak <NUM> and trough <NUM> and closely resembles the Plankian spectrum.

Packaged white light emitting devices in accordance with the invention comprising broadband LED chips comprise a single cavity <NUM> (<NUM> by <NUM>) SMD package containing a single <NUM> (<NUM> mil by <NUM> mil) <NUM> mW broadband LED chip die (MQW LED chip die) of dominant wavelength λd = <NUM> and FWHM <NUM>.

Table <NUM> tabulates phosphor compositions for nominal <NUM> and <NUM> SMD packaged white light emitting device in accordance with the invention, denoted Dev. <NUM> and Dev. <NUM> respectively.

As can be seen from Table <NUM>, in terms of phosphor composition: Dev. <NUM> comprises <NUM> wt% GAL520 (Lu<NUM>-x(Al<NUM>-yGay)<NUM>O<NUM>:Cex - λpe=<NUM>), <NUM> wt% CASN628 (Ca<NUM>-xSrxAlSiN<NUM>:Eu - λpe=<NUM>) and <NUM> wt% CASN650 (Ca<NUM>-xSrxAlSiN<NUM>:Eu - λpe=<NUM>) and Dev. <NUM> comprises <NUM> wt% GAL520 and <NUM> wt% CASN650.

Tables <NUM>, <NUM> and <NUM> tabulates measured optical test data for packaged light emitting devices Dev. <NUM> and Dev. It is to be noted from these tables that device Dev. <NUM> has a high luminous efficacy LE of <NUM> lm/Wopt and produces white light: (i) in which each of CRI R1 to CRI R15 is approximately <NUM> or higher, (ii) having a high CRI R11 ("Saturated Green") of <NUM>, (iii) having a high CRI R12 ("Saturated Blue") of <NUM>, (iv) having a high general color rendering index CRI Ra of <NUM>, (v) having a high color rendering index CRI Rall (average of CRI R1 to R15) of <NUM>, and (vi) having a high IEC TM-<NUM> fidelity index Rf of <NUM>. It is to be noted from these tables that device Dev. <NUM> has a high luminous efficacy LE of <NUM> lm/Wopt and produces white light having (i) in which each of CRI R1 to CRI R15 is approximately <NUM> or higher, (ii) having a high CRI R11 ("Saturated Green") of <NUM>, (iii) a high CRI R12 ("Saturated Blue") of <NUM>, (iv) a high general color rendering index CRI Ra of <NUM>, (v) a high color rendering index CRI Rall (average of CRI R1 to R15) of <NUM>, and (vi) a high IEC TM-<NUM> fidelity index Rf of <NUM>. The lower value of CRI R12 of <NUM> compared with the values of CRI R1 to R8 and R10 to R15 (Tables <NUM> and <NUM>) can be increased to <NUM> or higher by adjusting the phosphor composition for example increasing the wt%. of CASN650 though this may reduce the luminous efficacy slightly.

<FIG> shows normalized intensity versus wavelength (nm) for (i) Dev. <NUM> (solid line) and (ii) Plankian spectrum (dashed line) for a CCT that is the same as that of Dev. <NUM> (<NUM>). As can be seen from the figure, the spectrum (thick solid line) closely resembles the Plankian spectrum and exhibits three peaks 1382a, 1382b and 1382c separated by troughs 1386a and 1386b at about <NUM> and <NUM> respectively the combination of which corresponds to the broadband blue excitation light and a trough <NUM> in the cyan region (<NUM>) of the spectrum. It is believed that the lower value of CRI R12 of <NUM> compared with the values of CRI R1 to R11 and R13 to R15 (Tables <NUM> and <NUM>) results from the trough 1386b which drops below the Plankian spectrum and the trough due to the difference in the wavelength of the blue light emissions generated by the multiple different quantum wells of the MQW LED chip. The value of CRI R12 can be increased to <NUM> or higher by configuring the quantum wells of the MQW LED chip to reduce the difference in blue light emissions.

<FIG> shows normalized intensity versus wavelength (nm) for (i) Dev. <NUM> (solid line) and (ii) Sunlight Spectrum (dashed line) for a CCT that is the same as that of Dev. <NUM> (<NUM>). The Sunlight Spectrum is based on the CIE standard illuminant D55 and is a proportional blend from Plankian radiation below <NUM> to daylight for temperatures above <NUM>. As can be seen from the figure, the spectrum (thick solid line) closely resembles the Sunlight Spectrum and exhibits three peaks 1482a, 1482b and 1482c separated by troughs 1486a and 1486b at about <NUM> and <NUM> respectively the combination of which corresponds to the broadband blue excitation light and a trough <NUM> in the cyan region (<NUM>) of the spectrum. As described in relation to Dev. <NUM> (<FIG>) it is believed that the lower value of CRI R12 of <NUM> compared with the values of CRI R1 to R11 and R13 to R15 (Tables <NUM> and <NUM>) results from the trough 1486b which drops below the Plankian spectrum and the trough due to the difference in the wavelength of the blue light emissions generated by the multiple different quantum wells of the MQW LED chip. The value of CRI R12 can be increased to <NUM> or higher by configuring the quantum wells of the MQW LED chip to reduce the difference in blue light emissions.

Each spectrum shown in <FIG> and <FIG> has been normalized such each has a CIE <NUM> XYZ relative luminance Y=<NUM>.

COB Packaged white light emitting devices in accordance with the invention comprising broadband blue LED chips comprise a COB package containing twenty four <NUM> (<NUM> mil by <NUM> mil) <NUM> mW broadband LED chip die (MQW LED chip die) of dominant wavelength λd = <NUM> and FWHM <NUM>.

Table <NUM> tabulates phosphor compositions for a nominal <NUM> COB packaged white light emitting device in accordance with the invention, denoted Dev.

As can be seen from Table <NUM>, in terms of phosphor composition: Dev. <NUM> comprises <NUM> wt% GAL520 (Lu<NUM>-x(Al<NUM>-yGay)<NUM>O<NUM>:Cex - λpe=<NUM>) and <NUM> wt% CASN650 (Ca<NUM>-xSrxAlSiN<NUM>:Eu - λpe=<NUM>).

Tables <NUM>, <NUM> and <NUM> tabulates measured optical test data for the COB packaged white light emitting device Dev. It is to be noted from these tables that device Dev. <NUM> produces white light: (i) in which each of CRI R1 to CRI R15 is <NUM> or higher, (ii) having a high CRI R11 ("Saturated Green") of <NUM>, (iii) having a high CRI R12 ("Strong Blue") of <NUM>, (iv) having a high general color rendering index CRI Ra of <NUM>, (v) having a high color rendering index CRI Rall (average of CRI R1 to R15) of <NUM>, and (vi) a high IEC TM-<NUM> fidelity index Rf of <NUM>. Further, it is to be noted that while solid-state white light emitting devices in accordance with the invention generate high quality (color rendering) white light, they also have a high luminous efficacy LE of <NUM> lm/Wopt.

<FIG> shows normalized intensity versus wavelength (nm) for (i) Dev. <NUM> (thick solid line) and (ii) Plankian spectrum (dashed line) for a CCT that is the same as that of Dev. <NUM> (<NUM>). As can be seen from the figure, the spectrum (thick solid line) closely resembles the Plankian spectrum and exhibits three peaks 1582a, 1582b and 1582c separated by troughs 1586a and 1586b at about <NUM> and <NUM> respectively the combination of which corresponds to the broadband blue excitation light and a trough <NUM> in the cyan region (<NUM>) of the spectrum. It is believed that the lower value of CRI R12 of <NUM> compared with the values of CRI R1 to R11 and R13 to R15 (Tables <NUM> and <NUM>) results from the trough 1586b which drops below the Plankian spectrum and the trough due to the difference in the wavelength of the blue light emissions generated by the multiple different quantum wells of the MQW LED chip. The value of CRI R12 can be increased to <NUM> or higher by configuring the quantum wells of the MQW LED chip to reduce the difference in blue light emissions.

As can be seen from the figure, the spectrum (thick solid line) exhibits three peaks 1582a, 1582b and 1582c, and trough <NUM> and closely resembles the Plankian spectrum. Each spectrum has been normalized such each has a CIE <NUM> XYZ relative luminance Y=<NUM>.

While the invention arose in relation to full spectrum white light emitting devices for generating full spectrum white light having high color rendering qualities, light emitting devices in accordance with the invention comprising a broadband blue solid-state excitation source also offer advantages for light emitting devices that generate light with lower CRI Ra, for example greater than or equal to <NUM> or <NUM>. In such applications the use of a broadband blue solid-state excitation source can reduce damage to the human retina and/or reduce degeneration of the human macular compared with the known white LEDs that utilize narrow band blue excitation sources. It is believed that this is because the same blue photon energy is distributed over a greater wavelength range thereby reducing the intensity of the blue peak.

Tables <NUM>, <NUM> and <NUM> tabulates simulated optical test data for nominal <NUM>, CRI Ra <NUM> light emitting devices Com. <NUM> and Dev. <NUM> and illustrate the effect on light emitting device optical performance of using a broadband blue excitation source in accordance with the invention comprising a combination of narrowband LEDs of three different dominant wavelengths (λd1 = <NUM>, λd2 = <NUM> and λd3 = <NUM>) compared with using an excitation comprising narrowband LEDs of a single dominant wavelength (λd = <NUM>). It is to be noted from these tables that device Dev. <NUM> produces white light in which (i) there is an increase in CRI R11 ("Saturated Green") - <NUM> compared with <NUM> (ii) there is a substantial increase in CRI R12 ("Saturated Blue") - <NUM> compared with <NUM>. Further, it is to be noted that while the invention results in an increase in the quality (color rendering) of light, there is only a small reduction <NUM>% in luminous efficacy LE, and Dev. <NUM> has a high luminous efficacy LE of <NUM> lm/Wopt.

<FIG> are simulated emission spectra, normalized intensity (normalized to a CIE <NUM> XYZ relative luminance Y=<NUM>) versus wavelength (nm) for (i) Dev. <NUM> (solid line), (ii) Com. <NUM> (dotted) and (iii) Sunlight Spectrum (dashed line) for a CCT that is the same as that of Dev. <NUM> (i) (<NUM>).

Referring to <FIG>, it will be noted that the most pronounced effect on the emission spectra - spectral energy content - of the device in accordance with the embodiment (i.e. broadband blue solid-state excitation source comprising three solid-state light sources with different dominant wavelengths) compared with the comparative device (i.e. excitation source comprising solid-state light sources with a single dominant wavelength) are: (i) a broadening of the blue emission peak <NUM>, (ii) a reduction in the intensity of the blue emission peak <NUM> and (iii) a decrease in trough <NUM> in the cyan region of the spectrum at about <NUM>. As can be seen from the figure, the reduction of the blue emission peak <NUM> of Dev. <NUM> (compared with peak <NUM> of Com. <NUM>) and decrease in trough <NUM> results in the emission spectrum more closely resembling the Sunlight Spectrum. It is believed that this change in spectral energy content resulting from the use of a broadband blue excitation source, in this embodiment comprising three solid-state light sources, with different dominant wavelengths (blue light emissions) partially fills the trough in the cyan region of the spectrum accounts for the superior color rendering properties of the devices of the invention; in particular, the increase in CRI R11 and CRI R12.

A described above, a further advantage of the present invention is that white light emitting devices according to the invention can reduce or possibly prevent the likelihood of damage to the human retina and macula by reducing High Energy Visible (HEV) blue light in the wavelength region <NUM> - <NUM>. The blue photon energy (area under the peak) for the blue peaks <NUM> (Com. <NUM>) and <NUM> (Dev. <NUM>) are substantially the same. However, in the case of the peak <NUM> this energy is distributed over a greater wavelength range thereby reducing the intensity of the blue peak compared with the peak <NUM>. Since the white light emitting device of the present invention exhibits a reduction in the blue emission peak (i.e. HEV), the likelihood of damage being caused to the human retina and degeneration of the human macula is reduced or prevented.

In summary, it will be appreciated that light emitting devices in accordance with the invention comprising a broadband blue solid-state excitation source that generates broadband blue excitation light composed of a combination of at least three different wavelength blue light emissions have superior color rendering compared with known devices that comprise one or more narrowband solid-state light source(s) of a single dominant wavelength. For instance, the broadband blue solid-state excitation source may comprise, in illustrative examples not forming part of the claimed invention, two or more narrowband solid-state light sources (for example, LEDs), or one or more broadband solid-state light sources (for example, LED(s) having an active region with multiple or, in accordance with the claimed invention, three different quantum wells that are configured to generate blue light emissions of different peak wavelengths). Moreover, embodiments of the invention enable the implementation of full spectrum white light emitting devices that are characterized by generating white light having a color temperature in a range <NUM> to <NUM> with one or more of (i) a CRI R1 to CRI R15 of greater than or equal to <NUM>, (ii) a CRI R11 ("Saturated Green") of greater than or equal to <NUM>, (iii) a CRI R12 ("Saturated Blue") of greater than or equal to <NUM>, (iv) a CRI Ra greater than or equal to <NUM>, (v) a CRI Ra of greater than or equal to <NUM>, (vi) a IEC TM-<NUM> fidelity index Rf of greater than or equal to <NUM> and (vii) a luminous efficacy (LE) of greater than or equal to <NUM> lm/Wopt.

Claim 1:
A full spectrum white light emitting device (<NUM>) comprising:
a first photoluminescence material (<NUM>) for generating light with a peak emission wavelength in the range from <NUM> to <NUM>, and a second photoluminescence material (<NUM>) for generating light with a peak emission wavelength in the range from <NUM> to <NUM>; and
a broadband source (<NUM>) for generating excitation light with a dominant wavelength in the range from <NUM> to <NUM> and a FWHM of at least <NUM>, characterised in that the broadband source comprises a single InGaN/GaN LED (<NUM>) having an active region that directly generates blue light emissions of at least three different wavelengths (782a, 782b, 782c) using different quantum wells in a multiple-quantum-well (MQW) structure.