Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
  • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
  • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
  • C09K11/7766—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals
  • C09K11/7774—Aluminates
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
  • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
  • C09K11/61—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing fluorine, chlorine, bromine, iodine or unspecified halogen elements
  • C09K11/617—Silicates
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B33/00—Electroluminescent light sources
  • H05B33/12—Light sources with substantially two-dimensional radiating surfaces
  • H05B33/14—Light sources with substantially two-dimensional radiating surfaces characterised by the chemical or physical composition or the arrangement of the electroluminescent material, or by the simultaneous addition of the electroluminescent material in or onto the light source

Definitions

• the present disclosure generally relates to providing light sources that emit light having enhanced color spectrum characteristics such that human observers perceive enhanced color preference.
• the glass impregnated with Nd oxide causes a "depression" in the yellow region of the color spectrum, so that objects viewed under this light have an enhanced color contrast, especially red and green objects which are contrasted readily by an observer, such as a person in a room of a house.
• the removal of some yellow light via the filter also shifts the location of the chromaticity on the 1931 International Commission of Illumination (Commission Internationale de l’Éclairage, or CIE) color diagram to a point slightly below the blackbody locus, which generally creates the impression of whiter light to most observers.
• CIE International Commission of Illumination
• FIG. 1a provides a graph of three color matching functions, known as the XYZ tristimulus values that represent the chromatic response of a standard observer.
• the perceived color of an object is determined by the product of the illumination source spectrum, the reflectance spectrum of the object, and the three color matching functions. These functions are related to the response of the photoreceptors in the human eye, and can be thought of as the perception of blue (102), green (104), and red (106) light.
• FIG. 1b provides a graph for a product of a standard incandescent spectrum with the color matching functions for blue (132), green (134), and red (136) responses.
• FIG. 1c provides a graph for a product of a reveal ® incandescent spectrum with the color matching functions for blue (162), green (164), and red (166) responses.
• the green (164) and red (166) components are more distinct, with a peak separation of 53 nm, as compared to the red and green components of FIG. 1b. This distinction allows observers to more easily distinguish reds and greens with greater contrast and results in a more saturated appearance when yellow light is suppressed.
• SSL light sources for example LEDs or organic light-emitting diodes (OLEDs), may produce light directly from the semiconductor, e.g. a blue or red or other colored LED. Alternatively, the light may be produced by conversion of the high-energy light from the SSL, e.g.
• CRI color rendering index
• Fidelity metrics which include CRI, quantify an absolute difference from a reference illuminant, regardless of whether the test illuminant is perceived as being better or worse than the reference illuminant, and without consideration to whether the reference illuminant is actually preferred by most observers.
• Discrimination metrics quantify the total area of color space that may be rendered under the test illuminant, and are maximized at extreme levels of saturation and hue distortion.
• the existing color preference metrics have been developed to provide a quantitative measure of user color preference, but none provides a sufficient correlation to observer data, along with a target value to enable optimization of a light source; therefore, the metric cannot be used as a target parameter in a design optimization.
• Some of the more well-known metrics in the color preference category include Flattery Index (R f ), Color Preference Index (CPI), and Memory Color Rendering Index (MCRI). All three of these metrics have "ideal" configurations for the chromaticity coordinates of eight to ten test color samples, and each quantifies the deviation from these target values.
• the Flattery Index was the first metric to target preference and used ten color samples with unequal weighting.
• CPI Color Rendering Index
• the target chromaticity shifts were reduced to one-fifth of their experimental values, greatly reducing its correlation with observer responses to color preference.
• CPI maintained the experimental values for preferred chromaticity shifts, resulting in a better representation of color preference.
• CPI is very limited in its selection of test color samples, using the same eight, unsaturated test colors as CRI.
• Solid-state lighting technologies such as LEDs and LED-based devices often have superior performance when compared to incandescent lamps. This performance may be quantified by the useful lifetime of the lamp, lamp efficacy (lumens per watt), color temperature and color fidelity, and other parameters. It may be desirable to make and use an LED lighting apparatus also providing enhanced color preference qualities.
• CFL compact fluorescent
• LFL linear fluorescent
• LED lamps are known to enhance the color preference relative to their counterpart lamps that employ standard phosphors.
• GE Lighting has products of each of the first two types, also under the reveal ® brand name.
• LED light sources of the third type are known, for example in grocery applications to enhance the colors of meats, vegetables, and produce (e.g. fruit).
• Each of these existing light sources has employed either Nd-doped glass, or customized phosphors that reduce the amount of yellow light emitted by the light source in order to enhance color preference.
• Nd-doped glass or customized phosphors that reduce the amount of yellow light emitted by the light source in order to enhance color preference.
• the Nd filter in these existing light sources may typically be comprised of Nd 2 O 3 - doped glass.
• the yellow filter may be comprised of one of several other compounds of Nd or of Didymium (a mixture of the elements praseodymium and Nd) or other rare earths that preferentially absorb yellow light, embedded in various matrix host materials, for example glass, crystal, polymer, or other materials; or by some other dopant or coating on the glass that absorbs preferentially in the yellow range of wavelengths; or by the addition of a yellow absorber to any of the optically active components of the lamp or lighting system, such as a reflector or diffuser or lens, which may be a glass or polymer or metal or any other material that accommodates the yellow absorber.
• a reflector or diffuser or lens which may be a glass or polymer or metal or any other material that accommodates the yellow absorber.
• the exact peak wavelength and width of the yellow absorption may vary depending on the particular Nd or rare-earth compound and host material, but many combinations of Nd, Didymium and other rare-earth compounds and host materials may be suitable substitutions for the combination of Nd 2 O 3 -doped glass, as are some other yellow filters.
• the Nd or other yellow filter may be in the shape of a dome enclosing the light source, or may be any other geometric form enclosing the light source, such that most or all of the light in the yellow range of wavelengths passes through the filter.
• a composite light source includes at least one blue light source having peak wavelength in the range of about 400 nanometer (nm) to about 460 nm; at least one yellow-green garnet phosphor; at least one narrow-band red emitting down-converter; and wherein the composite light source has a Lighting Preference Index (LPI) of at least 120.
• LPI Lighting Preference Index
• a composite light source includes at least one blue light source having peak wavelength in the range of about 400 nanometer (nm) to about 460 nm; at least one YAG:Ce phosphor; at least one narrow red down-converter; and wherein a color appearance of the composite light source is represented as Oom v ⁇ 13.3 1 - ( Pw + 7 ° 0 095 ) + 569.8 - 0.004 * CCT, where Duv is a measure of the whiteness of the composite light source and DOMYAG is the dominant wavelength of the at least one YAG:Ce phosphor.
• a composite light source includes at least one blue light source having peak wavelength in the range of about 400 nanometer (nm) to about 460 nm; at least one yellow-green garnet phosphor; at least one broad red down-converter; and wherein the composite light source has a Lighting Preference Index (LP I) of at least 120.
• LP I Lighting Preference Index
• a composite light source includes at least one blue light source having peak wavelength in the range of about 400 nanometer (nm) to about 460 nm; at least one YAG:Ce phosphor; at least one broad-band red-emitting nitride phosphor; and wherein a color appearance of the composite light source is represented as
• Duv is a measure of the whiteness of the composite light source
• Peakm t is the peak wavelength of the at least one broad red nitride phosphor
• DOTHYAG is the dominant wavelength of the at least one YAG:Ce phosphor.
• a composite light source includes at least one blue light source having peak wavelength in the range of about 400 nanometer (nm) to about 460 nm; at least one yellow-green garnet phosphor; at least one narrow red down-converter; at least one broad red down-converter; and wherein the composite light source has a Lighting Preference Index (LPI) of at least 120.
• LPI Lighting Preference Index
• FIG. la illustrates a graph of the three color matching functions, the XYZ tristimulus values, or the chromatic response of a standard observer.
• FIG. lb illustrates a graph of the products of the three color matching functions with the spectrum for a standard incandescent lamp.
• FIG. 1c illustrates a graph of the products of the three color matching functions with the spectrum for a reveal® incandescent lamp.
• FIG. 2 illustrates a chart displaying the percentage of observers that selected each LED system.
• FIG. 3 illustrates a graph of the "White Line” (sometimes also called the “white-body curve” or“white-body locus”) and a graph of the blackbody curve (or blackbody locus, or BBL).
• White Line sometimes also called the "white-body curve” or“white-body locus”
• BBL blackbody locus
• FIG. 4a illustrates the ten main categories of hue in the a*-b* chromaticity plane, as prescribed in the Munsell classification system for color.
• FIG. 4b illustrates the radial and azimuthal components in the a*-b* chromaticity plane that comprise each Color Rendering Vector.
• FIG. 4c illustrates the Color Rendering Vectors (CRVs) at Munsell value 5 for a neodymium incandescent lamp.
• FIG. 5 illustrates an incandescent or halogen light source.
• FIG. 6a illustrates a graph of the relative light output versus wavelength (or the spectral power distribution (SPD)) of an incandescent light source of FIG. 5, and a blackbody light source.
• SPD spectral power distribution
• FIG. 6b illustrates a graph including a plot of the SPD of an incandescent light source, and a plot of the SPD of a reveal ® type incandescent light source.
• FIG. 7a illustrates a reveal ® type LED light source that includes one or more LEDs.
• FIG. 7b is an exploded view of the light source of FIG. 7a.
• FIG. 8 illustrates a graph including a plot of the SPD of a warm-white LED lamp comprising multiple blue LEDs each exciting a YAG phosphor and a red phosphor, and a plot of the SPD of a reveal ® type LED light source of FIG. 7a.
• FIG. 9 illustrates a reveal ® type compact fluorescent (CFL) light source.
• FIG.10 illustrates a graph including a plot of the spectral power distribution (SPD) of a reveal® type CFL light source of FIG.9, and a plot of the SPD of a reveal® type incandescent light source.
• SPD spectral power distribution
• FIG. 11 illustrates a graph of the SPD of a known light source having green and red phosphors having peak wavelengths separated sufficiently to produce a depression in the yellow wavelength range.
• FIG.12 illustrates a graph of the SPD of an LED light source from the prior art.
• FIG. 13 illustrates a graph of the SPD of the blue LED of a light source according to some embodiments.
• FIG. 14 illustrates a graph of the SPDs of five different yellow-green (YG) YAG:Ce phosphors according to some embodiments.
• FIG. 15 illustrates a graph of the SPDs of four different broad red (BR) nitride phosphors according to some embodiments.
• FIG. 16 illustrates the emission spectrum of a narrow red (NR) phosphor according to some embodiments.
• FIG. 17a illustrates the color coordinates in the 1931 CIE color system of the CIE standard illuminant D65, the color point of the YG phosphor YAG1 of FIG. 14, and the point on the spectrum locus (the perimeter of the CIE color space) of the resultant dominant wavelength of YAG1 according to some embodiments.
• FIG. 17c illustrates the color coordinates in the 1931 CIE color system of the blue LED of FIG. 13, the five YG YAG phosphors of FIG. 14, and the four different broad red nitride phosphors of FIG. 15 according to some embodiments.
• FIG. 18a illustrates the color coordinates in the 1931 CIE color system of the five commercially available YG YAG phosphors of FIG. 14, and also of a modification of each of the five YG YAG phosphors, where the peak wavelength is shifted by +10 nm, +5 nm, -5 nm, and–10 nm, providing a total of 25 SPDs representing a systematically parameterized, broad range of different YG YAG phosphors according to some embodiments.
• FIG. 18b illustrates the color coordinates in the 1931 CIE color system of the 25 systematically parameterized YG YAG:Ce phosphors of FIG. 18a, and also of 22
• FIG. 19a illustrates the color coordinates in the 1931 CIE color system of the four broad red nitride phosphors of FIG. 15, and also of a modification of each of the four broad red nitride phosphors, where the peak wavelength is shifted by +10 nm, +5 nm, -5 nm,–10 nm, providing a total of 20 SPDs representing a systematically parameterized, broad range of different broad red nitride phosphors according to some embodiments.
• FIG. 19b illustrates the color coordinates in the 1931 CIE color system of the 20 systematically parameterized broad red nitride phosphors of FIG. 19a, and also of 14 presently commercially available broad red nitride phosphors according to some
• FIG. 20 illustrates the relationship between the peak wavelengths and the dominant wavelengths of the 25 systematically parameterized YG YAG phosphors of FIG. 18a according to some embodiments.
• FIG. 21 illustrates the relationship between the peak wavelengths and the dominant wavelengths of the 20 systematically parameterized broad red nitride phosphors of FIG. 19a according to some embodiments.
• FIG. 22a illustrates the contour plot of Lighting Preference Index (LPI) versus dominant wavelength of the YG YAG phosphor on the x-axis, and the location of the color point of the light source in the CIE 1960 u-v color space, relative to the BBL at 2700 K, as quantified by Duv on the y-axis, where the red emitter is the NR phosphor of FIG. 16 according to some embodiments.
• LPI Lighting Preference Index
• FIG. 22b illustrates the contour plot of LPI versus dominant wavelength of the YG YAG phosphor on the x-axis, and the location of the color point of the light source in the CIE 1960 u-v color space, relative to the BBL at 3000 K, as quantified by Duv on the y-axis, where the red emitter is the NR phosphor of FIG. 16 according to some embodiments
• FIG. 23 illustrates the discrete runs represented by the dominant wavelength of the YG YAG phosphor, and by Duv, overlaid on the contour plot of the LPI response from FIG. 22a, where the red emitter is the NR phosphor of FIG. 16 according to some embodiments.
• FIG. 24 illustrates the SPD of the discrete run having the highest LPI value for a light source comprising a blue LED, a YG YAG phosphor, and a NR phosphor at 2700 K according to some embodiments.
• FIG. 25a illustrates a family of analytic approximations to each of the LPI contours at 2700 K from FIG. 22a where the red emitter is the NR phosphor of FIG. 16, overlaid on the actual LPI contours according to some embodiments.
• FIG. 25b illustrates a family of analytic approximations to each of the LPI contours at 3000 K from FIG. 22b where the red emitter is the NR phosphor of FIG. 16, overlaid on the actual LPI contours according to some embodiments.
• FIGS. 27a-h illustrate the contour plots at 2700 K of LPI versus dominant wavelength of the YG YAG phosphor on the x-axis, and Duv on the y-axis, where the red emitter is the broad red nitride phosphor of FIG. 15 having peak wavelength of 610 nm (FIG. 27a), 620 nm (FIG. 27b), 630 nm (FIG. 27c), 640 nm (FIG. 27d), 650 nm (FIG. 27e), 660 nm (FIG. 27f), 670 nm (FIG. 27g), 680 nm (FIG. 27h) according to some embodiments.
• the red emitter is the broad red nitride phosphor of FIG. 15 having peak wavelength of 610 nm (FIG. 27a), 620 nm (FIG. 27b), 630 nm (FIG. 27c), 640 nm (FIG. 27d),
• FIGS. 28a-h illustrate the contour plots at 3000 K of LPI versus dominant wavelength of the YG YAG phosphor on the x-axis, and Duv on the y-axis, where the red emitter is the broad red nitride phosphor of FIG. 15 having peak wavelength of 610 nm (FIG. 28a), 620 nm (FIG. 28b), 630 nm (FIG. 28c), 640 nm (FIG. 28d), 650 nm (FIG. 28e), 660 nm (FIG. 28f), 670 nm (FIG. 28g), 680 nm (FIG. 28h) according to some embodiments.
• the red emitter is the broad red nitride phosphor of FIG. 15 having peak wavelength of 610 nm (FIG. 28a), 620 nm (FIG. 28b), 630 nm (FIG. 28c), 640 nm (FIG. 28d),
• FIG. 29 illustrates the SPD of the discrete run having the highest LPI value for a light source comprising a blue LED, a YG YAG phosphor, and a broad red nitride phosphor at 2700 K according to some embodiments.
• FIGS. 30a-e illustrate a family of analytic approximations to each of the LPI contours at 2700 K from FIGS. 27d-h, overlaid on the actual LPI contours where the red emitter is the broad red nitride phosphor of FIG. 15, having peak wavelength of 640 nm (FIG. 30a), 650 nm (FIG. 30b), 660 nm (FIG. 30c), 670 nm (FIG. 30d), 680 nm (FIG. 30e) according to some embodiments.
• FIGS. 31a-e illustrate a family of analytic approximations to each of the LPI contours at 3000 K from FIGS. 28d-h, overlaid on the actual LPI contours where the red emitter is the broad red nitride phosphor of FIG. 15, having peak wavelength of 640 nm (FIG. 31a), 650 nm (FIG. 31b), 660 nm (FIG. 31c), 670 nm (FIG. 31d), 680 nm (FIG. 31e) according to some embodiments.
• FIGS. 32a-h illustrate the contour plots at 2700 K of LPI versus dominant wavelength of the YG YAG phosphor on the x-axis, and Duv on the y-axis, where the red emitter is comprised of 75% the NR phosphor of FIG. 16 and 25% the broad red nitride phosphor of FIG. 15 having peak wavelength of 610 nm (FIG. 32a), 620 nm (FIG. 32b), 630 nm (FIG. 32c), 640 nm (FIG. 32d), 650 nm (FIG. 32e), 660 nm (FIG. 32f), 670 nm (FIG. 32g), 680 nm (FIG. 32h) according to some embodiments.
• the red emitter is comprised of 75% the NR phosphor of FIG. 16 and 25% the broad red nitride phosphor of FIG. 15 having peak wavelength of 610 nm (FIG. 32a), 620
• FIGS. 33a-h illustrate the contour plots at 3000 K of LPI versus dominant wavelength of the YG YAG phosphor on the x-axis, and Duv on the y-axis, where the red emitter is comprised of 75% the NR phosphor of FIG. 16 and 25% the broad red nitride phosphor of FIG. 15 having peak wavelength of 610 nm (FIG. 33a), 620 nm (FIG. 33b), 630 nm (FIG. 33c), 640 nm (FIG. 33d), 650 nm (FIG. 33e), 660 nm (FIG. 33f), 670 nm (FIG. 33g), 680 nm (FIG. 33h) according to some embodiments.
• the red emitter is comprised of 75% the NR phosphor of FIG. 16 and 25% the broad red nitride phosphor of FIG. 15 having peak wavelength of 610 nm (FIG. 33a), 620
• FIG. 34 illustrates the SPD of the discrete run having the highest LPI value for a light source comprising a blue LED, a YG YAG phosphor, and a red emitter comprised of 75% NR phosphor and 25% broad red nitride phosphor at 2700 K according to some
• FIGS. 35a-h illustrate the contour plots at 2700 K of LPI versus dominant wavelength of the YG YAG phosphor on the x-axis, and Duv on the y-axis, where the red emitter is comprised of 50% the NR phosphor of FIG. 16 and 50% the broad red nitride phosphor of FIG. 15 having peak wavelength of 610 nm (FIG. 35a), 620 nm (FIG. 35b), 630 nm (FIG. 35c), 640 nm (FIG. 35d), 650 nm (FIG. 35e), 660 nm (FIG. 35f), 670 nm (FIG. 35g), 680 nm (FIG. 35h) according to some embodiments.
• the red emitter is comprised of 50% the NR phosphor of FIG. 16 and 50% the broad red nitride phosphor of FIG. 15 having peak wavelength of 610 nm (FIG. 35a), 620 n
• FIGS. 36a-h illustrate the contour plots at 3000 K of LPI versus dominant wavelength of the YG YAG phosphor on the x-axis, and Duv on the y-axis, where the red emitter is comprised of 50% the NR phosphor of FIG. 16 and 50% the broad red nitride phosphor of FIG. 15 having peak wavelength of 610 nm (FIG. 36a), 620 nm (FIG. 36b), 630 nm (FIG. 36c), 640 nm (FIG. 36d), 650 nm (FIG. 36e), 660 nm (FIG. 36f), 670 nm (FIG. 36g), 680 nm (FIG. 36h) according to some embodiments.
• the red emitter is comprised of 50% the NR phosphor of FIG. 16 and 50% the broad red nitride phosphor of FIG. 15 having peak wavelength of 610 nm (FIG. 36a), 620 n
• FIG. 37 illustrates the SPD of the discrete run having the highest LPI value for a light source comprising a blue LED, a YG YAG phosphor, and a red emitter comprised of 50% NR phosphor and 50% broad red nitride phosphor at 2700 K according to some
• FIGS. 38a-h illustrate the contour plots at 2700 K of LPI versus dominant wavelength of the YG YAG phosphor on the x-axis, and Duv on the y-axis, where the red emitter is comprised of 25% the NR phosphor of FIG. 16 and 75% the broad red nitride phosphor of FIG. 15 having peak wavelength of 610 nm (FIG. 38a), 620 nm (FIG. 38b), 630 nm (FIG. 38c), 640 nm (FIG. 38d), 650 nm (FIG. 38e), 660 nm (FIG. 38f), 670 nm (FIG. 38g), 680 nm (FIG. 38h) according to some embodiments.
• the red emitter is comprised of 25% the NR phosphor of FIG. 16 and 75% the broad red nitride phosphor of FIG. 15 having peak wavelength of 610 nm (FIG. 38a), 620
• FIGS. 39a-h illustrate the contour plots at 3000 K of LPI versus dominant wavelength of the YG YAG phosphor on the x-axis, and Duv on the y-axis, where the red emitter is comprised of 25% the NR phosphor of FIG. 16 and 75% the broad red nitride phosphor of FIG. 15 having peak wavelength of 610 nm (FIG. 39a), 620 nm (FIG. 39b), 630 nm (FIG. 39c), 640 nm (FIG. 39d), 650 nm (FIG. 39e), 660 nm (FIG. 39f), 670 nm (FIG. 39g), 680 nm (FIG. 39h) according to some embodiments.
• the red emitter is comprised of 25% the NR phosphor of FIG. 16 and 75% the broad red nitride phosphor of FIG. 15 having peak wavelength of 610 nm (FIG. 39a), 620
• FIG. 40 illustrates the SPD of the discrete run having the highest LPI value for a light source comprising a blue LED, a YG YAG phosphor, and a red emitter comprised of 25% NR (narrow red) phosphor and 75% broad red nitride phosphor at 2700 K according to some embodiments.
• FIG. 41 illustrates the maximum LPI achievable at 2700 K as a function of the BR (broad red) nitride peak wavelength for different compositions of the red emitter according to some embodiments.
• the term“light source” may mean any source of visible light, e.g. the semiconductor, or LED, or OLED; or the down-converter such as a phosphor or quantum dot; or remote down-converter, or down-converter coated onto or embedded into a reflector or refractor; or a multi-channel combination or composite of several such light sources; or a system such as a lamp or luminaire or fixture comprising such light sources.
• LPI Lighting Preference Index
• the enhanced color preference may be due to a combination of enhanced color contrast and enhanced whiteness, and the LPI color metric may enable quantitative optimization of color preference by tailoring the spectral power distribution of the light source.
• the individual light sources may be commercially available or easily manufactured blue LEDs, yellow-green garnet phosphors, broad red nitride phosphors, and narrow red phosphors, but combined in novel ways as described in the present disclosure. This may be in contrast to the light sources described in patent application US 61/875403 and PCT/US2014/054868, incorporated herein by reference, wherein the light sources were represented as combinations of an actual blue LED, plus green and red light sources each represented by Gaussian distribution of wavelength that are characterized by a peak wavelength and a full-width at half-maximum (FWHM).
• the Gaussian distributions in the US 61/875403 and PCT/US2014/054868 patent applications are hypothetical
• the combined light sources may be combinations of a commercially available blue or violet LED, a yellow-green garnet phosphor, and either a broad red nitride phosphor or a narrow red phosphor, or a combination of a broad and narrow red phosphor. Other suitable light sources may be used.
• the yellow-green (YG) phosphor may contain a garnet fluorescent material comprising 1) at least one element selected from the group consisting of Y, Lu, Sc, La, Gd, Tb, and Sm, and 2) at least one element selected from the group consisting of Al, Ga, and In, and being activated with Ce.
• the garnet phosphor may be further restricted to yttrium aluminum garnet (YAG, Y 3 Al 5 O 12 ) doped with Ce, i.e.
• Red phosphors may be defined for the purpose of this invention as having FWHM in two ranges: narrow FWHM ⁇ about 60 nm and broad FWHM > about 60 nm.
• BR nitride phosphors materials may absorb UV and blue light strongly and may emit efficiently between about 600 nm and 670 nm, with FWHM of about 80 nm to about 120 nm, providing very strong emission in the deep red, but at the expense of relatively poor luminous efficacy (lumens per watt, LPW).
• a broad red (BR) nitride phosphor is typically represented by the general formula CaAlSiN 3 :Eu 2+ .
• narrow red (NR) phosphors may absorb blue light strongly and may emit efficiently between about 610 nm and 660 nm with little deep red or near-infrared emission.
• NR phosphors include those based on complex fluoride materials activated by Mn 4+ , such as those described in U.S. Pat. No. 7,358.542.
• the Mn 4+ doped phosphors have the formula A x [MF y ]:Mn 4+ wherein A (alkali) is Li, Na, K, Rb, Cs, or a combination thereof; M (metal) is Si, Ge, Sn, Ti, Zr, AI, Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd, or a combination thereof; x is the absolute value of the charge of the [MF y ] ion; y is 5, 6 or 7. Therefore, LPW may be maximized compared to red phosphors that have significant emission in the deeper red where eye sensitivity is poor. Color saturation may also typically be enhanced, especially if the peak of the NR phosphor lies beyond about 620 nm.
• a NR phosphor may comprise K 2 [SiF 6 ]:Mn 4+
• PFS manganese-doped potassium fluoro-silicate
• LPI as disclosed herein accounts for both preferred color appearance (saturation and hue distortion) as well as preferred shifts in color point away from the Planckian (blackbody) locus.
• LPI is a predictive metric that quantifies consumer preference.
• LPI can be used as a design tool for optimizing spectra for color preference.
• a strong correlation for LPI has been found with preliminary observer testing, and the optimization capability of LPI as an accurate predictive preference metric is proven through additional studies. In an observer study with 86 participants, four discrete LED systems were designed to different enhanced levels of LPI, ranging from 114 to 143.
• FIG. 2 illustrates the percentage of observers that selected each LED system as their preferred environment. As shown, the highest percentage of observers (42%) preferred light source D having an LPI of 143, while the smallest percentage of observers (11%) preferred light source A having an LPI of 114.
• LPI The formula for LPI as described herein is based on an observer set within the age range of 21 to 27 years, with a gender distribution of 58% male and 42% female, a race distribution of 92% Caucasian and 8% Asian, and a geographical distribution within North America. However, this does not diminish the effectiveness of LPI, as presently defined herein, to quantify and optimize the level of color preference for an arbitrary light source spectrum such that if that test light source is built and the test illuminant is observed by a population having color preferences similar to those of a particular test population, then the test light source will be preferred relative to other light sources that score lower on the LPI scale by that test population.
• spectra or light sources optimized for high LPI, and having LPI greater than conventional light sources exhibit higher color preference among observers (having similar color preference bias to those in our dataset) than any of the conventional light sources.
• a variation of the lumen for example the scotopic lumen, is defined that differs from the traditional photopic lumen, and the definition of the scotopic lumen enables the discovery and development of light sources having increased or optimized scotopic lumen efficiency, that would not invalidate the effectiveness of the discoveries and developments of light sources that had provided, and continue to provide, increased or optimized photopic lumens, since the photopic lumen had been rigorously defined, even though it was not universally appropriate in all lighting applications.
• LPI objectively defines a quantitative color preference metric that most closely correlates with a limited population of observers for which color preference data was available.
• the LPI metric is a function of two parameters: the Whiteness of the illumination source and the Color Appearance of objects illuminated by the source. The specific LPI function is defined below, after explanation of Whiteness and Color Appearance.
• Whiteness refers to the proximity of the color point to the "White Line” on the chromaticity diagram, where the“White Line” is defined in the following publication: “White Lighting", Color Research & Application, volume 38, #2, pp. 82-92 (2013), authors M.S. Rea & J. P. Freyssinier (henceforth, the "Rea reference”). The Rea reference is hereby incorporated by reference.
• the“White Line” is defined by the color points in Table 1 below, as reported in CCX and CCY color coordinates for selected color temperatures from 2700 K to 6500 K.
• ometimes also called the“white-body line”, “white-body curve”, or“white-body locus”
• the“white-body line” is slightly above the blackbody curve 302 at high color temperatures (e.g., above 4000 K) and significantly below it at lower color temperatures.
• illumination on the“White Line” may correspond to human perception of what is “white” light.
• the “White Line” is proposed for a wide range of color temperatures, but for color temperatures between about 2700 K and about 3000 K (these are Correlated Color Temperature (CCT) values that consumers often prefer), the "White Line” is about 0.010 Duv below the blackbody locus, wherein Duv represents the distance from the blackbody locus in u-v chromaticity space.
• Equation (1) [0083] Equation (1):
• Duv for purposes of Equation (1), is the distance of the color point from the Planckian locus in u-v space (note: values below the blackbody line are negative in Equation (1)). For example, for a point at 0.010 below the blackbody, one would insert -0.010 into Equation (1).
• the Whiteness can be approximated by inspection of the position of the color point in FIG. 3, without undue experimentation; e.g., if the illumination source has a color point on the“White Line”, it will similarly have a Whiteness value of unity).
• LPI increases as the color point of the illumination source approaches the“White Line”, and decreases as it moves away in either direction.
• Color Appearance is a composite measure of color rendering, which is a function of the Net Saturation Value (NSV) of the illumination source (e.g., relatively higher LPI values are obtained for NSV that show an enhanced saturation, but are not overly saturated), and the Hue Distortion Value (HDV); (e.g., relatively higher LPI values are obtained for HDV that show a minimal or zero hue distortion).
• NSV Net Saturation Value
• HDV Hue Distortion Value
• the lighting preference index (LPI) metric was developed using an unbiased selection of test color samples, by selecting an array of colors using the complete database of 1600 corrected Munsell glossy spectral reflectances. These 1600 colors would be understood by the person of ordinary skill in the art, especially in view of M.W. Derhak & R.S. Berns, "Analysis and Correction of the Joensuu Munsell Glossy Spectral Database," Color and Imaging Conference, 2012(1), 191-194 (2012). Using this array of colors allows for coverage of a significant fraction of color space utilizing the Munsell classification system of hue, value, and chroma.
• each color in this array is defined by the Munsell system in terms of its hue (which has 10 categories with 4 subcategories in each, for 40 total items), chroma (ranging from 0 to 16), and value (ranging from 0 to 10).
• the 10 categories of hue are depicted and labeled in FIG. 4a. All levels of saturation, or chroma, and hue are weighted equally and treated in a statistical count approach, following a similar method as discussed in“Statistical approach to color quality of solid-state lamps,” IEEE J. Sel. Top. Quantum Electron., 15(6), 1753 (2009), authors A. Zukauskas, R. Vaicekauskas, F. Ivanauskas, H. Vaitkevicius, P. Vitta, and M.S. Shur.
• the color points of all 1600 color samples are calculated, as rendered by both the illumination source (i.e., the test illuminant) and by a CIE reference illuminant, or Planckian radiator, at the same color temperature.
• the CIE reference illuminant has a spectrum which is determined from the CCT of the illumination source, using Planck’s law for blackbody radiation. Planck’s law defines radiance of the light source B (in W/sr ⁇ m 3 ) as a function of wavelength ⁇ ( (in meters) and absolute temperature T (in K) as: where h is
• a blackbody is a physical body that is an ideal absorber, that is, it absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. It is also an ideal emitter: at every frequency, it emits as much energy as– or more energy than– any other body at the same temperature.
• CRV color rendering vectors
• a CRV is a representation of the magnitude and direction of a color appearance shift with respect to the reference illuminant.
• FIG. 4b illustrates the components contained in each CRV.
• the radial component 401, or ⁇ C ab quantifies the shift in chroma, or saturation, where shifts away from the origin signify increases in saturation and shifts toward the origin signify decreases in saturation.
• the azimuthal component 403, or ⁇ h ab quantifies the change in hue and can be represented by an angular change, in radians.
• FIG. 4c represents the CRVs 402 at Munsell value 5 for a neodymium incandescent lamp, a product commonly preferred by consumers.
• the neodymium lamp produces enhanced saturation, particularly in the red and green components (at the right and left sides, respectively, of the vector plot).
• the approximate vector directions corresponding to the colors yellow Y, red R, purple P, blue B, and green G, are indicated in the insert 404.
• NSV Net Saturation Value
• Improved levels of saturation are indicated by increases in chroma ( ⁇ C ab > 0) beyond a threshold of average perceptual difference, but below an over-saturation limit. Decreased saturation levels ( ⁇ C ab ⁇ 0) are only counted if chroma is reduced beyond the same threshold of average perceptual difference.
• the average perceptual difference value is based on the following publication:“Evaluation of Uniform Color Spaces Developed after the Adoption of CIELAB and CIELUV”, Color Research and Application, volume 19, #2, pp. 105-121 (1994), authors M. Mahy, L. Van Eycken, & A. Oosterlinck, which found the average perceptibility radius to be 2.3 in CIELAB space.
• NSV i Individual NSV values are calculated for the 10 main hue categories in the Munsell system, and a total NSV is taken as the average over the 10 hues.
• NSV is defined by Equation (2) and Equation (3):
• Equation (3) [0094] Equation (3):
• ⁇ C ab is the radial component of the CRV and represents the shift in perceived chroma, or saturation
• i represents the hue category for the 10 main hue categories of the Munsell system.
• the change in saturation may not be perceived by a typical observer and is therefore not counted as either improved or worsened.
• the Hue Distortion Value represents a weighted percentage of test samples that are changing hue. While increased chroma (up to a limit) generally does contribute to attaining relatively higher LPI values, changes in hue are generally undesirable (although changes in hue are a relatively weaker contributory factor to the final LPI value than are chroma changes).
• the Munsell color system is typically divided into 40 hue subcategories (4 subcategories in each of the 10 main hue categories).
• ⁇ h ab > ⁇ /20 radians or 1/40 th of a circle
• ⁇ h ab value is weighted by the average ⁇ h ab value, scaled by the separation between hue sublevels ( ⁇ /20 radians).
• This additional weighting is used to account for very large amounts of hue distortion, where the percentage alone approaches a limit at very high percentage, as nearly all test colors experience hue distortion of surpassing the threshold to be counted.
• the direction of hue distortion is unimportant, so ⁇ h ab > 0 for distortion in both the clockwise and
• HDV i the average over the 10 hues.
• Equation (4) the average over the 10 hues.
• Equation (4)
• ⁇ h ab is the azimuthal component of the CRV and represents the shift in perceived hue
• i represents the hue category for the 10 main hue categories of the Munsell system, and is the average ⁇ h ab value for all colors within hue i.
• Equation (6) [00102] Equation (6):
• Equation (6) the HDV is weighted (i.e., divided by a factor) relative to NSV to provide the best match to observer preference responses.
• Equation 7 Equation 7:
• Equation (7)
• the parameter of“100” is chosen so that a reference blackbody illuminant scores a baseline value of 100 as with other lighting metrics.
• the weighting factors of 38% Whiteness and 62% Color Appearance have been chosen to provide the best fit to observer preference data. .
• Equation (8) An alternative "master" equation for LPI, which is merely a combination of equations (1), (6) and (7), is shown as Equation (8):
• the LPI metric may be determined by the following steps (not necessarily in this order):
• step (c) the whiteness of step (c) is calculated in parallel with the calculation of color appearance in steps (d)-(h). Then the whiteness and color appearance serve as inputs to the final step (i).
• color preference may also be quantified using a novel combination of existing color metrics, although with somewhat weaker, but acceptably strong, correlation to color preference data of observers.
• existing color metrics that separately represent saturation and color point relative to the BBL can be expected to approximate the color preference responses of observers within some limits of color space.
• LPI furthermore may combine the effects of saturation and color point with an optimal weighting of each to provide a single metric, rather than multiple metrics, which has been validated to be useful as a single-parameter optimization response that enables the design of spectra that will predictively elicit a targeted color preference response from observers.
• the separation between the peak or dominant wavelength of the YG phosphor and the red phosphor provides a close approximation to the color saturation portion of the LPI metric
• the Duv measure is a close approximation to the color point portion (i.e., whiteness) of the LPI metric.
• a single class of phosphors are used to provide the YG emission in the SPD of the light source; whereas two classes of phosphors, narrow having a single peak wavelength, and broad having various peak wavelengths, may be used to provide the red emission in the SPD of the light source.
• the separation between the peak or dominant wavelength of the YG phosphor and the peak wavelength of the red phosphor is quantified by holding the peak wavelength of the red phosphor fixed, while varying the dominant wavelength of the YG phosphor, thereby providing a direct measure of the separation between the YG and red phosphors.
• a light source comprising a blue LED, a YG YAG:Ce phosphor, and a NR or BR phosphor having a given peak wavelength, by the dominant wavelength of the YG phosphor, and Duv of the color point in the CIE 1960 u-v color space, as approximate substitutes for the more accurate LPI metric, with the advantage that some practitioners may find it easier to calculate the dominant wavelength of the YG phosphor and Duv responses than to calculate the LPI response, even though all of the details necessary to calculate the LPI response have been provided.
• FIG. 5 illustrates an incandescent light source or halogen light source 500 that includes one or more incandescent or halogen coils 502 within a glass dome 504.
• the glass dome 504 may be doped with neodymium oxide (Nd 2 O 3 ), as is provided in GE reveal ® type incandescent and halogen lamps.
• the light emitted from the coil or coils is similar to that of a blackbody spectrum, typically with a correlated color temperature (CCT) between about 2700 K and about 3200 K. This CCT range may be referred to as warm white.
• CCT correlated color temperature
• the Nd- doped glass dome 504 may function to filter out light in the yellow portion of the color spectrum, such that the light transmitted through the glass dome 504 of the light source 500 has an enhanced color preference, or color saturation, or color contrast capability that is typically preferred by a human observer relative to light emitted from the same light source without the Nd glass filter.
• the blackbody is likewise assigned the reference value of 100 for the LPI metric.
• LPI a value of 99.8 is considered to be a neutral value, not a maximum value.
• the CRI metric quantifies the degree to which a light source renders eight pastel test colors exactly the same as the blackbody reference, and so it is a color“fidelity” metric of limited scope in color space.
• the differences between the two SPDs is due entirely to the absorption of light by the Nd-doped glass, most of which occurs in the yellow range from about 570 nm to about 610 nm, and a weaker absorption in the green range from about 510 nm to about 540 nm.
• the color preference benefits accrued from the Nd absorption are due to the yellow absorption.
• An SPD may be plotted with an absolute scale of light intensity, e.g. with dimensions of Watts/nm or Watts/nm/cm 2 or other radiometric quantity, or it may be plotted in relative units, sometimes normalized to the peak intensity, as is provided here.
• the SPD plot 600 of the incandescent lamp shown in FIG. 6a shows it to be an exceptionally well-balanced light source because there are no significant spikes or holes at any wavelengths.
• Such a smooth curve that matches closely to the blackbody curve having the same CCT indicates outstanding color fidelity abilities.
• the incandescent lamp typically has a CRI of about 99.
• the Nd-incandescent lamp typically has a CRI of about 80. In spite of the lower CRI, most observers prefer the color rendering of the Nd-incandescent lamp over the incandescent lamp, especially for applications where organic objects are being illuminated, e.g.
• FIG. 7a illustrates a reveal ® type LED light source 700 that includes one or more LEDs (FIG. 7b), and FIG. 7b is an exploded view of the light source 700 of FIG. 7a.
• An LED is an example of a solid state lighting (SSL) component, which may include semiconductor LEDs, organic LEDs, or polymer LEDs as sources of illumination instead of legacy light sources such as incandescent bulbs that use electric filaments; or fluorescent tubes or high-intensity discharge tubes that use plasma and/or gas.
• SSL solid state lighting
• a light engine 712 comprising LEDs 706 and 708 and a printed circuit board 710 to which the LEDs are mounted, and which is attachable to a housing 704, so that, when assembled, the LEDs 706 and 708 are positioned within a glass dome 702 that is impregnated with neodymium oxide (Nd 2 O 3 ), such that most or all of the light emitted by the LEDs 706 and 708 passes through the dome 702.
• Nd 2 O 3 neodymium oxide
• housing 704 may be of different size and/or shape, and the solid state lighting components 706 and 708 may be connected directly and/or indirectly thereto during assembly.
• the light emitted from the LEDs may be comprised of a mixture of light from a blue LED 802, having peak wavelength in the range of about 400 to about 460 nm (e.g., royal blue InGaN), and YG light 804 having peak emission in the range of about 500 to about 600 nm created by the excitation of a phosphor material (such as a YAG:Ce phosphor) by the blue emission from the LED, and possibly also red light 806 having peak emission in the range of about 600 to about 670 nm created by the excitation of another phosphor (such as nitride or sulfide phosphor) by the blue emission from the LED.
• a blue LED 802 having peak wavelength in the range of about 400 to about 460 nm (e.g., royal blue InGaN)
• YG light 804 having peak emission in the range of about 500 to about 600 nm created by the excitation of a phosphor material (such as a YAG:Ce
• the mixed-light spectrum is also similar to that of a blackbody spectrum, but may include a depression in the wavelength range between the blue LED emission and the YG phosphor emission.
• the light source may have a correlated color temperature (CCT) between about 2700 K and about 3200 K (warm white), or it may have a higher CCT, perhaps as high as about 10,000 K or higher, or a lower CCT, perhaps as low as about 1800 K or lower.
• CCT correlated color temperature
• the Nd glass functions to filter out light in the yellow portion 808 of the color spectrum which may have been produced by the YG and red phosphors, such that the light 810 (the entire solid line plot) emitting from the glass dome of the light source 700 has an enhanced color preference, or color saturation or color contrast capability, or whiteness that is typically preferred by a human observer relative to light 800 emitted from the same light source without the Nd glass filter.
• Some conventional lamp types which include one or more low-pressure mercury (Hg) discharge lamps and special formulations of visible-light emitting phosphors (i.e., fluorescent (FL) or compact fluorescent (CFL) light sources) selected to reduce the amount of yellow light emitted by the light source are also known to enhance the color preference relative to their typical counterpart FL or CFL light source lamps without the special phosphor formulations.
• FIG. 9 illustrates a reveal ® type CFL light source 900 that includes a low-pressure Hg discharge tube 902 coated with a customized mix of phosphors 904 having relatively low emission in the yellow spectrum.
• the light source may also have a correlated color temperature (CCT) between about 2700 K and about 3200 K (warm white).
• CCT correlated color temperature
• the light source may have a higher CCT (e.g., as high as about 10,000 K or higher), or a lower CCT (e.g., as low as about 1800 K or lower).
• the mixed light spectrum plot 1000 of the light source 900 having a relatively low emission in the yellow portion of the spectrum may have an enhanced color preference, or color saturation, or color contrast capability that is typically preferred by a human observer relative to light emitted from the same light source having a traditional phosphor mix.
• Some additional conventional lamp types include one or more LEDs having green and red phosphors having peak wavelengths separated sufficiently to produce a depression in the yellow wavelength range and are used, for example, in grocery applications to enhance the colors of meats, vegetables, and produce (e.g. fruit).
• the light emitted from the LEDs may be comprised of a mixture of light from blue light emission 1102, having peak wavelength in the range of about 400 nm to about 460 nm created by emission from a blue LED, and green light emission 1104 having peak wavelength in the range of about 500 nm to about 580 nm and FWHM 1108 of about 80 nm created by the excitation of a green phosphor by the blue emission from the LED, and red light emission 1106 having peak emission in the range of about 600 nm to about 670 nm and FWHM 1110 of about 100 nm created by the excitation of a red phosphor by the blue emission from the LED.
• the mixed-light spectrum may have a depression in the wavelength range between the blue LED emission 1102 and the green phosphor emission 1104, and may include a second depression in the yellow wavelength range between the green phosphor emission 1104 and the red phosphor emission 1106.
• the light source may also have a CCT between about 2700 K and about 6000 K, or it may have a higher CCT, e.g., as high as about 10,000 K or higher, or a lower CCT, e.g., as low as about 1800 K or lower.
• the reduced emission in the yellow portion of the SPD plot 1100 resulting from the separation of the peak of the green phosphor emission 1104 at 528 nm and the peak of the red phosphor emission 1106 at 645 nm provides a light source spectrum plot 1100 resulting in an LPI of about 124.
• the relatively high LPI value in this known light source is due to the relatively narrow FWHM (about 80 nm) and the blue-shifted peak (at about 528 nm) of the green phosphor, which is not the same composition of a YG YAG:Ce phosphor of the embodiments of the present disclosure.
• FWHM of YG YAG:Ce phosphors in general have FWHM in a slightly broader range of about 110 to about 120 nm, and a range of peak wavelengths from about 530 nm to about 560 nm, as represented by the 25 different YAG phosphor embodiments described in one or more embodiments below.
• each spectrum is comprised of three components (nominally blue, green, and red) superimposed into a composite spectrum.
• the blue emission component 1302 is that of a blue LED, peak emission at about 450 nm, and having FWHM 1304 of about 15 nm. This wavelength was chosen to be representative of the typical blue LED presently used in most white light sources.
• Other suitable blue emission components may be used, having characteristics, such as peak wavelengths in the range of about 400 nm to about 460 nm, and having FWHM ⁇ about 50 nm.
• the LPI color metric is relatively much less sensitive to the blue emission than to the green and red emission. This can be understood from FIG.
• the results of this DOE may be expected to represent the results given by any blue light source having peak wavelength in the blue or violet range (e.g. about 400 to about 460 nm) and having any FWHM less than about 50 nm.
• the green component may be modelled using a family of 5 different YG YAG phosphor emissions (FIG. 14), having a range of peak wavelengths from about 540 nm to about 547 nm representing the usual range of
• the full- width-at-half-maximum (FWHM) e.g.
• a YG YAG phosphor may include the family of phosphors having a garnet fluorescent material comprising 1) at least one element selected from the group consisting of Y, Lu, Sc, La, Gd, Tb, and Sm, and 2) at least one element selected from the group consisting of Al, Ga, and In, and being activated with Ce, wherein the garnet phosphor is further restricted to yttrium aluminum garnet (YAG, Y 3 Al 5 O 12 ) doped with Ce, i.e. YAG:Ce 3+ .
• the red component may be modelled using a family of four different BR nitride phosphor emissions (FIG. 15) and a NR phosphor (FIG. 16).
• the BR nitride phosphor is typically represented by general formula of CaAlSiN 3 :Eu 2+ .
• These BR nitride phosphor materials absorb UV and blue light strongly and emit efficiently between about 600 nm and about 680 nm, e.g. 1502, with FWHM, e.g. 1504, of about 80 nm to about 120 nm, providing very strong emission in the deep red.
• NR phosphors (FIG.
• the Mn 4+ doped phosphors have the formula A x [MF y ]:Mn 4+ wherein A (alkali) is Li, Na, K, Rb, Cs, or a combination thereof; M (metal) is Si, Ge, Sn, Ti, Zr, AI, Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd, or a combination thereof; x is the absolute value of the charge of the [MF y ] ion; y is 5, 6 or 7.
• a (alkali) is Li, Na, K, Rb, Cs, or a combination thereof
• M (metal) is Si, Ge, Sn, Ti, Zr, AI, Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd, or a combination thereof;
• x is the absolute value of the charge of the [MF y ] ion; y is 5, 6 or 7.
• These materials absorb blue light strongly and emit efficiently between about
• the NR phosphor of this invention has a peak wavelength at about 631 nm, representing the commercially available PFS as described in U.S. Pat. No. 7,358.542, U.S. Pat. No. 7,497,973, and U.S. Pat. No. 7,648,649. Therefore, in one or more embodiments, in DoE runs that included only a NR phosphor, without a BR phosphor, the NR phosphor comprised only a single, unique red component. In other embodiments, this particular NR phosphor may be substituted by another NR phosphor having similar peak wavelength to provide color preference benefits very similar to those provided by the NR phosphor.
• the broad red component may be modelled using a family of 4 different BR nitride phosphor emissions, having a range of peak wavelengths from about 620 nm to about 670 nm, representing the usual range of commercially available, or easily manufactured broad red nitride phosphors. Therefore, in one or more embodiments, runs that included only a BR nitride phosphor, without a NR phosphor, the BR nitride phosphor included 4 different red components.
• FWHM full- width-at-half-maximum
• the DoE was divided into three groups, differentiated by the red phosphor: Group 1 comprising the NR PFS phosphor only (YAG + PFS); Group 2 comprising each of the 20 BR nitride phosphors separately (YAG + Nit) representing the commercially available red nitride phosphors; Group 3 comprising 3 ratios of BR power to NR power (emitted power summed over the full wavelength range of red emission, as provided in FIG. 15 and FIG. 16), in increments of 25%, so that (BR
• n 0.25, 0.50, 0.75 for each of the 20 BR nitride phosphors in combination with the single NR phosphor (YAG + PFS + Nit).
• Group 3a 0.25
• Group 3b 0.50
• the division of the DoE into 3 groups is a matter of convenience for communicating the results.
• a mixture of red nitride and PFS emitters may be used in one or more embodiments due to trade-offs in colorimetric and photometric capabilities of illuminants having NR vs. BR emitters, whereby the NR emitter may enhance efficacy by reducing the amount of radiation at wavelengths in the far tail of the photopic eye response curve, whereas the BR emitter may enhance color rendering or color preference, at the expense of efficacy.
• LPI Lighting Preference Index
• FIGs 17-21 serve to define each of the 25 YG and 20 BR phosphors in the DoE by its dominant wavelength.
• the peak wavelength of a light source is that wavelength at which the emitted intensity is a maximum
• the dominant wavelength is that wavelength of pure monochromatic light that most closely matches the hue (perceived color) of the light source.
• the dominant wavelength of a light source is formally defined (see Wyszecki and Stiles, Color Science: Concepts and Methods,
• FIG. 17c is the same as FIG. 17b, but showing the 4 commercially available broad red nitride phosphors 1728 used in the DoE (as in FIG. 15), instead of the single NR phosphor.
• the color points 1844 of 22 commercially available YG YAG phosphors representing essentially the full range of YG YAG:Ce phosphors that are presently commercially available, are shown in a zoomed-in view of the 1931 CIE color space 1800, along with the 25 YG phosphors 1834 of FIG. 18a that were used in the DoE. It is apparent from comparison of the color points of the group of 25 systematically
• FIG. 19a the color points 1938 of the 20 BR phosphors used in the DoE are shown in a zoomed-in view of the 1931 CIE color space 1900: 4 commercially available broad red nitride phosphors, along with a modification of each of the four commercially available broad red nitride phosphors, where the emission spectrum is shifted by +10 nm, +5 nm, -5 nm, and–10 nm, representing a systematically parameterized, broad range of different BR phosphors.
• 4 commercially available broad red nitride phosphors, along with a modification of each of the four commercially available broad red nitride phosphors, where the emission spectrum is shifted by +10 nm, +5 nm, -5 nm, and–10 nm, representing a systematically parameterized, broad range of different BR phosphors.
• the color points 1948 of 14 commercially available broad red nitride phosphors representing essentially the full range of broad red nitride phosphors that are presently commercially available, are included along with the 20 BR phosphors 1938 of FIG. 19a that were used in the DoE. It is apparent from comparison of the color points of the group of 20 systematically parameterized BR phosphors used in the DoE with the 14 commercially available broad red nitride phosphors indicate that the range of broad red nitride phosphors that are presently commercially available is fully represented in the DoE.
• the peak wavelength of a light source is that wavelength at which the emitted intensity is a maximum
• the dominant wavelength is that wavelength of pure monochromatic light that most closely matches the hue (perceived color) of the light source
• FIG. 20 shows the relationship between dominant and peak wavelengths for the 25 YG phosphors used in the DoE.
• the dominant wavelength is generally longer than the peak wavelength for each of the YG phosphors. This may be primarily due to the asymmetry of the phosphor emission, as seen in FIG.
• FIG. 21 shows the relationship between dominant and peak wavelengths for the 20 BR phosphors used in the DoE. As shown herein, the dominant wavelength is generally shorter than the peak wavelength for each of the BR phosphors. This may be primarily due to the extremely long wavelengths of the phosphor emission to the right of each peak wavelength as seen in FIG. 15, where the long-wavelength tails extend far beyond the wavelengths of the eye response (FIG.
• each of the embodiments herein may be described as having a blue light source, a yellow-green garnet phosphor, a narrow red down-converter and/or a broad red down-converter, it is noted that at least one blue light source may be used, at least one yellow-green garnet phosphor may be used, at least one narrow red down-converter may be used, and/or at least one broad red down-converter may be used.
• the colorimetric response of interest, LPI is plotted in FIG. 22a vs. Dom YAG (x-axis) and Duv (y-axis) of the color point at 2700 K.
• LPI is plotted in FIG. 22b vs. Dom YAG and Duv of the color point at 3000 K.
• LPI f(CCT, Duv, Dom YAG ), including polynomial terms as high as quartic, and all resultant variable interactions, providing a transfer function having Adjusted R 2 > 0.99.
• LPI f(CCT, Duv, Dom YAG )
• the particular SPD 2400 in the Group 1 DoE (YAG + PFS) having the highest LPI value of about 137, corresponding to Dom YAG of about 559 nm, and Duv at about -0.010, with CCT 2700 K, is illustrated in FIG. 24, showing the peak wavelength of the blue LED 2402 at about 450 nm, the peak wavelength of the YG YAG:Ce phosphor 2404 at about 531 nm, the peak wavelength of the NR PFS phosphor 2406 at about 631 nm; and is compared with the SPD 604 of a reveal® incandescent lamp and with the SPD 602 of a blackbody emitter, each having similar CCT.
• an LPI of at least 140 may be achieved with YAG and a narrow red down-converter having a more favorable wavelength than the peak wavelength of the PFS phosphor which is fixed at 631 nm, or by using two or more narrow red down-converters, having different peak wavelengths.
• the nearly monotonically increasing LPI with decreasing Dom YAG may be primarily due to the separation in wavelength between the YG emitter and the narrow red emitter, diminishing the typically large emission in the yellow, or even creating a depression in the yellow portion of the spectrum (e.g. about 570 to about 600 nm) which enhances the perceived saturation of red-green opponent colors, and blue-yellow opponent colors.
• LPI contours might be approximated in a closed-form analytical formula containing only the terms Duv to prescribe Whiteness, and Dom YAG as a surrogate for Color Appearance.
• the general absence of high-order irregularities in the LPI contours having values of 120 and higher suggests that such an analytical approximation to those high-LPI contours might have a relatively simple format that holds for most or all of the LPI contours to be generated in the DoE.
• the visual appearance of the high- LPI contours suggest that an ellipse might provide the best fit for the high-LPI contours.
• Equation (9) has provided agreement between the exact LPI contour and the elliptical approximation for every LPI contour in FIGS. 22a,b having LPI of 120 or higher: [00142] Equation (9)
• Equation (9) The trend of LPI vs. CCT may be accurately described by the simple linear term in Equation (9).
• the values for coefficients, a and b, in Equation (9) are given in Table 2 below for each LPI value of 120 and higher for FIGS. 22a,b.
• Equation (9a) Equation (9a)
• the dashed-line elliptical approximations deviate from the respective exact LPI contours by an amount not exceeding about 2 points in LPI at any location, on any LPI contour, having a value of 120 or higher. It is known that differences in CRI values of less than about 5 points, and especially less than about 2 points, are generally not perceivable by most observers.
• LPI values of less than about 5 points, and especially less than about 2 points are generally not perceivable by most observers. This is to be expected, since the LPI scale has been intentionally made proportional to the CRI scale, in order to provide a similar degree of quantitative differentiation with LPI as is obtained with CRI.
• the colorimetric response of interest, LPI is plotted in FIG. 27a vs. Dom YAG (x-axis) and Duv (y-axis) of the color point at 2700 K, for the case of a BR phosphor having peak wavelength (Peak Nit ) of 610 nm.
• the range of Peak Nit that were used in the Group 2 DoE is shown in FIG. 21 to be from about 610 nm to about 680 nm, including 20 different BR phosphors in that range.
• the Dom YAG and Duv values of the 250 unique combinations of 25 different Dom YAG values at each of five different Duv values as shown in FIG. 23 and used in the Group 1 DoE are the same 250 unique combinations of Dom YAG and Duv that were used in the Group 2 DoE in combination with each of the 20 different BR phosphors.
• the fine spacing between Dom YAG values on the x-axis and the Duv values on the y-axis of the 250 unique SPDs used in the Group 1 DoE have been found to provide smooth interpolations between discrete SPDs actually used in the DoE.
• the five Duv levels were chosen to illustrate the effect of color point, or Duv, on LPI. Other suitable Duv levels may be used.
• similar contour plots may be presented for a continuum of Duv levels within the range of Duv presented herein, with similar trends being realized.
• the SPD having the highest LPI (about 142) among the 2500 SPDs at 2700 K in the Group 2 DoE is shown in FIG. 29.
• the particular SPD 2900 in the Group 2 DoE (YAG + Nit) having the highest LPI value of about 142, corresponding to Dom YAG of about 559 nm, and Duv at about -0.010, with CCT 2700 K, is illustrated in FIG.
• the nearly monotonically increasing LPI with decreasing Dom YAG and increasing Peak Nit may be primarily due to the separation in wavelength between the YG emitter and the BR emitter, diminishing the typically large emission in the yellow, or even creating a depression in the yellow portion of the spectrum (e.g. about 570 to about 600 nm) which enhances the perceived saturation of red-green opponent colors, and blue-yellow opponent colors.
• Equation (10) Similar to Equation (9) for the Group 1 DoE, a general form for an elliptical approximation to the LPI curves of the Group 2 DoE, Equation (10) below provides agreement to within 1 or 2 points in LPI between the exact LPI contour and the elliptical approximation for every LPI contour in FIGS.27a-h and FIGS.28a-h having LPI of 120 or higher. Since the transfer function for LPI in Group 2 has an additional variable, Peak Nit , relative to Group 1, Equation (10) is necessarily more complex than Equation (9).
• Equation (10a) Equation (10a) below.
• the Group 3 DoE (YAG + PFS + Nit) included all combinations of the 1 blue LED, 25 YG YAG:Ce phosphors, and 20 BR Nitride phosphors, described above, resulting in 500 unique combinations of emitters (1 B x 25 YG x 1 NR x 20 BR) at each of 3 different ratios of BR power to NR power (emitted power summed over the full wavelength range of red emission, as provided in FIG. 15 and FIG.
• Peak Nit used in the Group 3 DoE is from about 610 nm to about 680 nm, including 20 different BR phosphors in that range.
• LPI The colorimetric response of interest, LPI, is plotted in FIGS. 32a-h vs.
• the SPD having the highest LPI (about 137) among the 2500 SPDs at 2700 K in the Group 3a DoE is shown in FIG. 34.
• the particular SPD 3400 in the Group 3a DoE (YAG + PFS + Nit, where n 0.25) having the highest LPI value of about 137,
• the SPD having the highest LPI (about 138) among the 2500 SPDs at 2700 K in the Group 3b DoE is shown in FIG. 37.
• the particular SPD 3700 in the Group 3b DoE (YAG + PFS + Nit, where n 0.50) having the highest LPI value of about 138,
• the colorimetric response of interest, LPI is plotted in FIGS. 38a-h vs.
• the SPD having the highest LPI (about 140) among the 2500 SPDs at 2700 K in the Group 3c DoE is shown in FIG. 40.
• the Dom YAG and Duv values of the 250 unique combinations of 25 different Dom YAG values at each of five different Duv values as shown in FIG. 23 and used in the Group 1 DoE and Group 2 DoE are the same 250 unique combinations of Dom YAG and Duv that were used in the Group 3 DoE, in combination with each of the 20 different BR phosphors.
• the fine spacing between Dom YAG values on the x-axis and the Duv values on the y-axis of the 250 unique SPDs used in the Group 3 DoE have been found to provide smooth interpolations between discrete SPDs actually used in the DoE. While five Duv levels were used herein to illustrate the effect of color point, or Duv, on LPI, other suitable Duv levels may be used.
• Peak Nit values Peak Nit > 660 nm
• Equation (9) for the Group 1 DoE and Equation (10) for the Group 2 DoE a general form for an elliptical approximation to the LPI curves of the Group 3 DoE, may be produced.
• the LED light source 700 may include one or more groups of LEDs 706 and 708 (numbering adopted from FIG. 7a and 7b for convenience) that may each consist of one or more blue LEDs coated with YG YAG:Ce phosphor and a NR phosphor.
• This first exemplary embodiment is termed "YAG + PFS".
• the portion of the blue light generated by the blue LED that is not absorbed by the phosphor materials combined with the light emitted by the phosphor materials may provide light which appears to the human eye as being nearly white in color.
• the spectrum of a YAG + PFS light source having enhanced color preference may be composed of a blue LED peak emission in the range of about 400 nm to about 460 nm, a YG peak emission in the range of about 530 nm to about 557 nm created by the excitation of a YAG:Ce phosphor by the blue emission from the LED, and a red peak emission at about 631 nm created by the excitation of a NR phosphor by the blue emission from the LED, as depicted in FIG. 24.
• the spectrum may differ from that of a blackbody in that it may include a depression in the wavelength range between the blue LED emission and the YG phosphor emission, and may include a depression in the yellow wavelength range between the YG phosphor and the NR phosphor.
• the light source in this first exemplary embodiment may have a CCT between about 2700 K and about 3200 K. In one or more embodiments, the light source may have a higher CCT (e.g., as high as about 10,000 K or higher), or a lower CCT (e.g., as low as about 1800 K or lower).
• the reduced emission in the yellow portion of the color spectrum may result from the separation of the peaks of the YG phosphor and the NR phosphor that may be created by the relatively narrow width and relatively long peak wavelength of the NR PFS phosphor.
• the reduced emission may be further enhanced in the yellow portion of the color spectrum by a relatively short peak wavelength of the YG phosphor, compared with a typical YG YAG:Ce phosphor.
• the depression of the spectrum in the yellow portion, if sufficiently deep, and the enhanced emission in the red and green relative to a blackbody emitter, may provide a light source having an enhanced color preference, or color saturation, or color contrast capability that is typically preferred by a human observer relative to light emitted from the same light source employing a typical blue and YG and red phosphor combinations that do not produce a sufficiently deep depression in the yellow portion.
• the curve 2400 is the particular SPD that provided the maximum LPI of 137 from among the 250 combinations of SPDs in Group 1 (YAG + PFS) of the DoE.
• an LPI of about 137 is obtained, so that a human observer may perceive more saturated colors, enhanced whiteness, and a much more preferred color appearance when utilizing the YAG + PFS spectrum 2400 than is possible by using light sources typically having LPI of 120 or less.
• a second exemplary embodiment of a light source providing slightly reduced color preference (LPI) for a YAG + PFS light source than the first embodiment, the peak and dominant wavelengths of the YG YAG:Ce phosphor 2404 in FIG. 24 are shifted slightly to a longer wavelength than the optimal peak and dominant wavelengths of 531 nm and 559 nm of the first embodiment.
• LPI slightly reduced color preference
• an LPI of about 135 or greater is obtained, so that a human observer may perceive more saturated colors, enhanced whiteness, and a much more preferred color appearance when utilizing the YAG + PFS spectrum 2400 than is possible by using light sources typically having LPI of 120 or less, and only very slightly less so than the first embodiment having LPI of about 137.
• a third exemplary embodiment of a light source providing further reduced color preference (LPI) for a YAG + PFS light source than the first and second embodiments, but still exceeding that of the prior art, the peak and dominant wavelengths of the YG YAG:Ce phosphor 2404 in FIG. 24 are shifted to even longer wavelengths than the optimal peak and dominant wavelengths of 531 nm and 559 nm of the first embodiment.
• LPI color preference
• an LPI of about 120 or greater is obtained, so that a human observer may perceive more saturated colors, enhanced whiteness, and a more preferred color appearance when utilizing the YAG + PFS spectrum 2400 than is possible by using light sources typically having LPI of 120 or less, although noticeably less so than the first embodiment having LPI of about 137.
• the LED light source 700 may include one or more groups of LEDs 706 and 708 that may each consist of one or more blue LEDs coated with YG YAG:Ce phosphor and a BR nitride phosphor (YAG + Nit), where the portion of the blue light generated by the blue LED that is not absorbed by the phosphor materials, combined with the light emitted by the phosphor materials provides light which appears to the human eye as being nearly white in color (again, figure element numbers are adopted from FIG. 7a and 7b solely for convenience).
• the spectrum of a YAG + Nit light source having enhanced color preference may be composed of a blue LED peak emission in the range of about 400 nm to about 460 nm, a YG peak emission in the range of about 530 nm to about 557 nm created by the excitation of a YAG:Ce phosphor by the blue emission from the LED, and a red peak emission in the range of about 610 nm to about 680 nm created by the excitation of a BR nitride phosphor by the blue emission from the LED, as depicted in FIG. 29.
• the spectrum may differ from that of a blackbody in that it may include a depression in the wavelength range between the blue LED emission and the YG phosphor emission, and it may include a depression in the yellow wavelength range between the YG phosphor and the BR phosphor.
• the light source may have a CCT between about 2700 K and about 3200 K. In one or more embodiments the light source may have a higher CCT (e.g., as high as about 10,000 K or higher), or a lower CCT (e.g., as low as about 1800 K or lower).
• the reduced emission in the yellow portion of the color spectrum may result from the separation of the peaks of the YG phosphor and the BR phosphor that may be created primarily by the relatively long peak wavelength of the BR nitride phosphor.
• the reduced emission in the yellow portion of the color spectrum may be further enhanced by a relatively short peak wavelength of the YG phosphor, compared with a typical YG YAG:Ce phosphor.
• the depression of the spectrum in the yellow, if sufficiently deep, and the enhanced emission in the red and green relative to a blackbody emitter, may provide a light source having an enhanced color preference, or color saturation, or color contrast capability that may be preferred by a human observer relative to light emitted from the same light source employing a typical blue and YG and red phosphor combinations that do not produce a sufficiently deep depression in the yellow.
• the plot 2900 is the particular SPD that provided the maximum LPI of 142 from among the 5000 combinations of SPDs in Group 2 (YAG + Nit) of the DoE.
• the LPI score of 142 is very high (in one or more embodiments, the maximum possible LPI may be about 150), meaning that a human observer will perceive more saturated colors, enhanced whiteness, and a much more preferred color appearance when utilizing the YAG + PFS spectrum 2900 than is possible by using light sources typically having LPI of 120 or less.
• an LPI of about 142 is obtained, so that a human observer may perceive more saturated colors, enhanced whiteness, and a much more preferred color appearance when utilizing the YAG + Nit spectrum 2900 than is possible by using light sources typically having LPI of 120 or less.
• a fifth exemplary embodiment of a light source providing slightly reduced color preference (LPI) for a YAG + Nit light source than the fourth exemplary embodiment
• the peak and dominant wavelengths of the YG YAG:Ce phosphor 2904 in FIG. 29 are shifted slightly to longer wavelengths than the optimal peak and dominant wavelengths of 531 nm and 559 nm of the fourth embodiment, and the peak wavelength of the nitride red phosphor 2906 in FIG. 29 is shifted to a shorter wavelength than the optimal peak wavelength of 680 nm of the fourth embodiment.
• Dom YAG may be as long as about 568 nm, and Peak Nit may be as short as about 660 nm, while Duv of the color point remains near -0. ween about -0.005 and about -0.014), with CCT of about 2700 K to about 3000 K, and the combination of Dom YAG and Duv satisfies Equation 10,
• an LPI of about 135 or greater is obtained, so that a human observer may perceive more saturated colors, enhanced whiteness, and a much more preferred color appearance when utilizing the YAG + Nit spectrum 2900 than is possible by using light sources typically having LPI of 120 or less, and only very slightly less so than the fourth embodiment having LPI of about 142.
• Dom YAG may be as long as about 573 nm, and Peak Nit may be as short as about 630 nm or 640 nm, while Duv of the color point is ideally near -0.010, but may be anywhere in the range of about 0.000 to about -0.019, with CCT of about 2700 K to about 3000 K, and the combination of Dom YAG and Duv satisfy Equation 10,
• an LPI of about 120 or greater is obtained, meaning that a human observer will perceive more saturated colors, enhanced whiteness, and a more preferred color appearance when utilizing the YAG + Nit spectrum 2900 than is possible by using light sources typically having LPI of 120 or less .
• the LED light source may include one or more groups of LEDs and that may each consist of one or more blue LEDs coated with YG YAG:Ce phosphor and a combination of NR PFS phosphor and BR nitride phosphor (YAG + PFS + Nit), where the portion of the blue light generated by the blue LED that is not absorbed by the phosphor materials, combined with the light emitted by the phosphor materials, may provide light which appears to the human eye as being nearly white in color.
• LPI color preference
• the spectrum of a YAG + PFS + Nit light source having enhanced color preference may be composed of a blue LED peak emission in the range of about 400 nm to about 460 nm, a YG peak emission in the range of about 530 nm to about 557 nm created by the excitation of a YAG:Ce phosphor by the blue emission from the LED, a red peak emission at about 631 nm created by the excitation of a NR PFS phosphor by the blue emission from the blue LED, and additional red emission having a peak in the range of about 610 nm to about 680 nm created by the excitation of a BR nitride phosphor by the blue emission from the blue LED, as depicted in FIGS.
• the spectrum shown in FIGS. 34, 37 and 40 may differ from that of a blackbody spectrum in that it may include a depression in the wavelength range between the blue LED emission and the YG phosphor emission, and it may include a depression in the yellow wavelength range between the YG phosphor and the red phosphors.
• the light source may have a CCT between about 2700 K and about 3200 K. In one or more embodiments, the light source may have a higher CCT (e.g., as high as about 10,000 K or higher), or a lower CCT (e.g., as low as about 1800 K or lower).
• the reduced emission in the yellow portion of the color spectrum may result from the separation of the peaks of the YG phosphor and the red phosphors that may be created by the relatively narrow width and relatively long peak wavelength of the NR PFS phosphor and the relatively long peak wavelength of the BR nitride phosphor.
• the reduced emission in the yellow portion may be further enhanced by a relatively short peak wavelength of the YG phosphor, compared with a typical YG YAG:Ce phosphor.
• the depression of the spectrum in the yellow portion, if sufficiently deep, and the enhanced emission in the red and green portions relative to a blackbody emitter, may provide a light source having an enhanced color preference, or color saturation, or color contrast capability that may be typically preferred by a human observer relative to light emitted from the same light source employing typical blue and YG and red phosphor combinations that do not produce a sufficiently deep depression in the yellow.
• the division of the DoE into 3 groups is a matter of convenience for communicating the results.
• the peak wavelength of the blue LEDs 3402, 3702, and 4002 occurs at about 450 nm
• the peak and calculated dominant wavelengths of the YG phosphor 3404, 3704, and 4004 occur at about 531 nm and 559 nm respectively
• the peak wavelength of the NR phosphor 3406, 3706, and 4006 occurs at about 631 nm
• the corresponding SPD at 3000 K may appear very similar, with similar CRI and LPI values.
• LPI scores of 137, 138, and 140, for n 0.25, 0.50, and 0.75, respectively, are high (in one or more embodiments, the maximum possible LPI may be about 150), so that a human observer may perceive more saturated colors, enhanced whiteness, and a much more preferred color appearance when utilizing the YAG + PFS spectra 3400, 3700, and 4000 than is possible by using light sources typically having LPI of 120 or less.
• an LPI of about 140 to 142 is obtained, so that a human observer may perceive more saturated colors, enhanced whiteness, and a much more preferred color appearance when utilizing the YAG + PFS + Nit spectra 3400, 3700, and 4000 than is possible by using light sources typically having LPI of 120.
• the peak and dominant wavelengths of the YG YAG:Ce phosphor 3404, 3704, and 4004 in FIGS. 34, 37 and 40 are shifted slightly to longer wavelengths than the optimal peak and dominant wavelengths of 531 nm and 559 nm of the seventh embodiment, and the peak wavelengths of the nitride red phosphor 3408, 3708, and 4008 in FIGS. 34, 37 and 40 are shifted to a shorter wavelength than the optimal peak wavelength of 680 nm of the seventh embodiment.
• Dom YAG may be as long as about 566 nm, and Peak Nit may be as short as about 660 nm while Duv of the color point remains near -0.010 (between about -0.008 and about -0.012), with CCT of about 2700 K to about 3000 K.
• an LPI of about 135 or greater is obtained, so that a human observer may perceive more saturated colors, enhanced whiteness, and a much more preferred color appearance when utilizing the YAG + PFS + Nit spectra 3400, 3700, and 4000 than is possible by using light sources typically having LPI of 120 or less, and only very slightly less so than the seventh embodiment having LPI of about 142.
• a ninth exemplary embodiment of a light source providing further reduced color preference (LPI) for a YAG + PFS + Nit light source than the seventh embodiment, but still exceeding that of light sources typically having LPI of 120 or greater, the peak and calculated dominant wavelengths of the YG YAG:Ce phosphor 3404, 3704, and 4004 in FIGS. 34, 37 and 40 are shifted slightly to longer wavelengths than the optimal peak and dominant wavelengths of 531 nm and 559 nm of the seventh embodiment, and the peak wavelength of the nitride red phosphor 3408, 3708, and 4008 in FIGS. 34, 37 and 40 is shifted to a shorter wavelength than the optimal peak wavelength of 680 nm of the seventh embodiment.
• LPI color preference
• Dom YAG may be as long as about 572 nm, and Peak Nit may be as short as about 620 nm, while Duv of the color point is ideally near -0.010, but may be anywhere in the range of about 0.000 to about -0.018, with CCT of about 2700 K to about 3000 K.
• an LPI of about 120 or greater is obtained, so that a human observer may perceive more saturated colors, enhanced whiteness, and a more preferred color appearance when utilizing the YAG + PFS + Nit spectra 3400, 3700, and 4000 than is possible by using light sources typically having LPI of 120 or less.
• a yellow-absorbing filter such as neodymium (Nd) glass, or a Nd compound, or a comparable yellow filter
• a yellow-absorbing filter such as neodymium (Nd) glass, or a Nd compound, or a comparable yellow filter
• Nd neodymium
• a neodymium (Nd) glass dome may be placed over the LED light engine, and the Nd glass dome may function to suppress yellow light to further enhance the perception of red and green vibrancy.
• the peak wavelength of the red phosphor may be moved to shorter wavelengths or the FWHM of the red phosphor to be increased.
• the inclusion of a yellow filter may provide further enhanced color preference (higher LPI) by further enhancing the depression in the yellow.

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