Warm white LED spectrum especially for retail applications

Abstract

The invention provides a lighting device (100) configured to provide lighting device light (101), the lighting device (100) comprising a solid state light source (10) configured to provide blue light (11) having a peak wavelength (λ.sub.PWL) selected from the range of 430-455 nm, a first luminescent material (210) configured to convert part of the blue light (11) into first luminescent material light (211) and a second luminescent material (220) configured to convert part of one or more of the blue light (11) and the first luminescent material light (211) into second luminescent material light (221), wherein the solid state light source (10), the first luminescent material (210), and the second luminescent material (220) are selected to provide at a first setting of the lighting device (100) white lighting device light (101) having a CRI of at least 90, a R.sub.9 value of at least 70, and a R.sub.50 value of at maximum 465 nm, wherein the R.sub.50 value is defined as a first wavelength (λ.sub.50) in a spectral distribution of the white lighting device light (101) at the first setting, wherein the first wavelength (λ.sub.50) is a wavelength closest to the peak wavelength (λ.sub.PWL) but at a longer wavelength than the peak wavelength (λ.sub.PWL) of the blue light (11) where the peak intensity (I.sub.50) is 50% of the intensity (I.sub.PWL) at the peak wavelength (λ.sub.PWL).

Claims

1. A lighting device configured to provide lighting device light, the lighting device comprising a solid state light source configured to provide blue light having a peak wavelength selected from the range of 430-455 nm, a first luminescent material configured to convert part of the blue light into first luminescent material light and a second luminescent material configured to convert part of one or more of the blue light and the first luminescent material light into second luminescent material light, wherein the solid state light source, the first luminescent material, and the second luminescent material are selected to provide at a first setting of the lighting device white lighting device light having a CRI of at least 90, a gamut area index (GAI) of at least 100, a R.sub.9 value of at least 70 and a R.sub.50 value of at maximum 455 nm, wherein the R.sub.50 value is defined as a first wavelength (λ.sub.50) in a spectral distribution of the white lighting device light at the first setting, wherein the first wavelength (λ.sub.50) is a wavelength closest to the peak wavelength (λ.sub.PWL) but at a longer wavelength than the peak wavelength (λ.sub.PWL) of the blue light where the peak intensity (I.sub.50) is 50% of the intensity (I.sub.PWL) at the peak wavelength (λ.sub.PWL), and wherein the first luminescent material light has an intensity in one or more of the green wavelength range and yellow wavelength range having a CIE u.sub.1′, and the second luminescent material light has an intensity in one or more of the orange wavelength range and red wavelength range having a CIE u.sub.2′, wherein the first luminescent material and the second luminescent material are selected to provide said first luminescent material light and said second luminescent material light defined by a maximum ratio of CIE u.sub.1′ and CIE u.sub.2′ being CIE u.sub.2′=1.58*CIE u.sub.1′+0.255, and a minimum ratio of CIE u.sub.1′ and CIE u.sub.2′ being CIE u.sub.2′(221)=2.3*CIE u.sub.1′+0.04.

2. The light emitting device according to claim 1, wherein the blue light has a peak wavelength (λ.sub.PWL) selected from the range of 435-445 nm.

3. The light emitting device according to claim 1, configured to provide white lighting device light having a gamut area index (GAI) in the range of 101-120 at the first setting.

4. The light emitting device according to claim 1, configured to provide white lighting device light at the first setting having an R.sub.50 value of at maximum 450 nm.

5. The light emitting device according to claim 1, configured to provide white lighting device light at the first setting having a CIE v′ of at least 0.005 below the black body locus (BBL), and having a CIE v′ of at maximum 0.025 below the black body locus (BBL).

6. The light emitting device according to claim 1, configured to provide white lighting device light with −0.014≤D.sub.uv≤−0.005 at the first setting.

7. The light emitting device according to claim 1, wherein the first luminescent material has an intensity in one or more of the green wavelength range and yellow wavelength range and the CIE v′ value is in the range of 0.55-0.58, and the second luminescent material has an intensity in one or more of the orange wavelength range and red wavelength range and the CIE v′ value is in the range of 0.52-0.55.

8. The light emitting device according to claim 1, configured to provide white lighting device light at the first setting having a correlated color temperature selected from the range of 2700-4000 K.

9. The light emitting device according to claim 1, wherein the first luminescent material comprises M.sub.3A.sub.5O.sub.12:Ce.sup.3+, wherein M is selected from the group consisting of Sc, Y, Tb, Gd, and Lu, wherein A is selected from the group consisting of Al, Ga, Sc and In.

10. The light emitting device according to claim 1, wherein the second luminescent material comprises MAlSiN.sub.3:Eu, wherein M comprises one or more elements selected from the group consisting of barium (Ba), strontium (Sr) and calcium (Ca), wherein the second luminescent material comprises different MAlSiN.sub.3:Eu compounds, with a first compound with M at least comprising Ca and a second compound with M at least comprising Sr.

11. The light emitting device according to claim 1, wherein: the solid state light source is configured to provide blue light having a peak wavelength (λ.sub.PWL) selected from the range of 435-445 nm the solid state light source has a LED die, wherein the lighting device comprises a light converter comprising said first luminescent material and said second luminescent material, and wherein the light converter is in physical contact with the LED die; the first luminescent material comprises M.sub.3A.sub.5O.sub.12:Ce.sup.3+, wherein M is selected from the group consisting of Sc, Y, Tb, Gd, and Lu, wherein A is selected from the group consisting of Al, Ga, Sc and In; the second luminescent material comprises MAlSiN.sub.3:Eu, wherein M comprises one or more elements selected from the group consisting of barium (Ba), strontium (Sr) and calcium (Ca), wherein the second luminescent material comprises different MAlSiN.sub.3:Eu compounds, with a first compound with M at least comprising Ca and a second compound with M at least comprising Sr; and the light emitting device is configured to provide white lighting device light at the first setting having an R.sub.50 value of at maximum 455 nm.

12. The light emitting device according to claim 1, configured to provide white lighting device light having spectral distributions (Watt) in the range of 11-13% for the blue light, 40-47% for the first luminescent material light, and 30-48% for the second luminescent material light, at the first setting.

13. A lighting system comprising the light emitting device according to claim 1 and a control system configured to control the light emitting device.

14. Use of the light emitting device according to claim 1 in retail lighting.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

(2) FIGS. 1a-1c schematically depict some aspects of the invention;

(3) FIG. 2 shows spectra of premium white products made using a GaYAG green (or green/yellow) phosphor (GaYAG) in combination with first red or orange phosphor and second orange or red phosphor. Mixture of red phosphors adjusted to get CRI≥90 and R.sub.9=70); the wavelengths indicate the peak wavelength of the LED used; PW930 indicates a reference premium white product;

(4) FIG. 3 shows the R.sub.50 (nm) (indicates in the graph as λ.sub.50) for the different spectra shown in FIG. 2;

(5) FIG. 4 shows CIE u′ v′ color points calculated using a standard 2° observer (open circle) and using the CIE 2006-10° observer (open squares). The label gives the R.sub.50 (nm) of the 4 samples;

(6) FIG. 5 shows CIE v′ color point (CIE 2006-10° observer) as a function of the R.sub.50 (nm). Starting color point was (0.249, 0.512) in all cases (calculated using the standard CIE 2° observer);

(7) FIG. 6 shows the change in chroma for hue bin 1-16 as defined in IES TM30-15 (Scale −0.15 to +0.15) for white LED spectra with varying PWL, compared with PW930 and CDM; and

(8) FIG. 7 shows R.sub.50 (nm) as a function of the PWL of the blue LED for different green phosphors (GaYAG versus LuAG).

(9) The schematic drawings are not necessarily on scale.

(10) FIG. 8: example of a general colour rendering index graphic for a test light source, which was used in the study by Jost et al. The graphic shows the changes in colorfulness and hue shifts for the eight CIE1974 test-color samples (defined in CIE publication 13.3-1995). The dashed circle indicates a distance of unity to the origin, whereas the solid line, connecting the points for the test light source, indicates the relative increase in gamut area. The arrows in the graphic represent the change in colorfulness and hue for the eight test-color samples, relative to the reference illuminant.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(11) FIG. 1a schematically depicts an embodiment of a lighting device 100 as described herein. The lighting device 100 comprises a light source 10 configured to provide blue light source light 11, a first luminescent material 210 configured to convert at least part of the light source light 11 into first luminescent material light 211 with light intensity in one or more of the green spectral region and yellow spectral region and a second luminescent material 220 configured to convert (i) at least part of the light source light 11, or (ii) at least part of the light source light 11 and at least part of the first luminescent material light 211 into second luminescent material light 221 with light intensity in the orange and/or red spectral region.

(12) Further, the lighting device comprises a light exit face 110. Herein in the embodiment of FIG. 1a, this may be the downstream face of a window 105.

(13) The terms “upstream” and “downstream” relate to an arrangement of items or features relative to the propagation of the light from a light generating means (here the especially the first light source), wherein relative to a first position within a beam of light from the light generating means, a second position in the beam of light closer to the light generating means is “upstream”, and a third position within the beam of light further away from the light generating means is “downstream”.

(14) In FIG. 1b this is the downstream face of a converter 200. Here, in FIGS. 1a-1c the converter 200 comprises the first luminescent material 210 and the second luminescent material 220, e.g. a layers (FIG. 1a), or as mixture (FIGS. 1b-1c). Note that the converter 200 may also include materials and/or layers other than the first luminescent material 210 and the second luminescent material 220. In FIG. 1a, the converter is configured upstream of the light exit face, here upstream of window 105. Especially, when using separate layers of the first luminescent material 210 and the second luminescent material 220, the latter is configured downstream of the former, in order to further facilitate absorption of the first luminescent material light 211. Would the second luminescent material 220 substantially not absorb first luminescent material light 211, then the order of the layers may also be revered. Further, also mixtures may be applied (see FIGS. 1b-1c).

(15) Further, the lighting device 100 is configured to provide lighting device light 101 downstream from said light exit face 110. Here, as shown in FIG. 1a, the lighting device light 101 comprises one or more of said light source light 11, said first luminescent material light 211, and said second luminescent material light 221. As indicated above, the second luminescent material 220 is configured to be at least partly saturated with (i) light source light 11, or (ii) light source light 11 and first luminescent material light 211.

(16) The distance between the first and/or the second luminescent materials and the light source 10, especially the light emitting surface, is indicated with reference d1, which is (substantially) zero in the case of FIG. 1c (d1 not depicted in FIG. 1c) and which may be in the range of 0.1-50 mm, especially 1-20 mm in e.g. the embodiment of FIGS. 1a-1b. In the schematically depicted embodiment, the distance d1 is the distance between a light exit surface (or light emitting surface) 122 of a solid state light source 120, such as an LED die.

(17) FIG. 1b schematically further depicts a control system 130, which may include a user interface 140. Hence, FIG. 1b also schematically depicts a lighting system 1000.

(18) The lighting device 100 may especially be applied for providing white lighting device light 101.

(19) Hence, amongst others the invention provides a light source for providing blue light, a first luminescent material for providing first luminescent material light and a second luminescent material for providing second luminescent material light, which are configured to provide white lighting device light (at a first setting) having spectral distributions (Watt) in the range of 11-14%, especially 11.9-12.7% for the blue light, 31-35%, especially 32.7-33.5% for the first luminescent material light, and 52-57%, especially 53.9-55.3%, for the second luminescent material light. Even more especially, the invention provides the light source for providing blue light, the first luminescent material for providing first luminescent material light and the second luminescent material for providing second luminescent material light, wherein the second luminescent material comprises a first second luminescent material for providing first second luminescent material light, and a second luminescent material for providing second luminescent material light, which are configured to provide white lighting device light (at a first setting) having spectral distributions (Watt) in the range of 11-14%, especially 11.9-12.7% for the blue light, 31-35%, especially 32.7-33.5% for the first luminescent material light, and 28-50%, especially 29.8-47.9% for first second luminescent material light and 5-27%, especially 6-25.5%, for the second luminescent material light. Especially, this applies to first luminescent materials having a relatively narrow band width, such as in the range of 60-90 nm.

(20) Hence, amongst others the invention provides a light source for providing blue light, a first luminescent material for providing first luminescent material light and a second luminescent material for providing second luminescent material, which are configured to provide white lighting device light (at a first setting) having spectral distributions (Watt) in the range of 11-13%, especially 11.4-12.2% for the blue light, 40-47%, especially 41-45.9% for the first luminescent material light, and 41-49%, especially 42.1-47.6% for the second luminescent material light. Even more especially, the invention provides the light source for providing blue light, the first luminescent material for providing first luminescent material light and the second luminescent material for providing second luminescent material, wherein the second luminescent material comprises a first second luminescent material for providing first second luminescent material light, and a second luminescent material for providing second luminescent material light, which are configured to provide white lighting device light (at a first setting) having spectral distributions (Watt) in the range of 11-13%, especially 11.4-12.2% for the blue light, 40-47%, especially 41-45.9% for the first luminescent material light, and 0-16%, especially 0-14.6% for first second luminescent material light and 30-48%, especially 32-46%, for the second luminescent material light.

(21) Percentages of the spectral distribution (in the visible) add up to 100%.

(22) The effect of blue pump position in the final white spectrum influences the white ‘rendering’ and the gamut area. It appears that shifting the blue LED peak towards shorter wavelength leads to a better (=whiter) white ‘rendering’ and increases the gamut area. The extension of the gamut area is in the yellow and blue orientation, and thus does not lead to a severe efficiency penalty. Oversaturation in the yellow-blue orientation also occurs for high pressure discharge lamps like CDM-elite and CDM-ultimo, which are generally seen as giving the best general retail lighting spectrum.

(23) Amongst others, a LED based light device is proposed wherein one or more of the following applies:

(24) 1. R.sub.50 (nm)≤455 nm, more especially R.sub.50 (nm)≤450 nm

(25) 2. CRI≥90

(26) 3. R.sub.9≥70

(27) 4. CCT=2700-4000 K

(28) 5. −0.005≥Duv≥−0.014 (i.e. about 6-14 points below BBL)

(29) 6. R.sub.g≥100

(30) Especially, at least the first condition applies. Even more especially, also one or more of the other conditions apply. In this way, white ‘rendering’, a high color saturation index, a perception as CDM-elite and good efficiency can be obtained. Good white ‘rendering’ can be obtained by adding violet LEDs, but that is costly and has a significant efficiency penalty. High color saturation index can be obtained by adding deep red phosphor, i.e. increasing the red saturation, but this also has a significant efficiency penalty. To mimic the perception of CDM-elite, oversaturation in the yellow-blue orientation may be needed. We have surprisingly found that the object of the invention can be realized by shifting the blue peak in the white spectrum to shorter wavelength. This can be realized in various manners: tuning the blue LED wavelength and/or tuning the absorption of the (green) phosphor. LEDs were made using GaYAG and a mixture of a first red or orange phosphor and second orange or red phosphor; the ratio of the two red phosphors was adjusted to get an R.sub.9 of 70 and a CRI ≥90, see also FIG. 2. Blue LEDs with different pump wavelength (PWL) between 440 and 455 nm were used. The target color point was 0.249, 0.512 in CIE u′ v′ for all samples. The ratio of the different red/orange luminescent materials was varied to keep CRI and R.sub.9 essentially equal.

(31) The blue peak position in the final spectrum will depend on the phosphors used. The blue peak position in the final white spectrum is characterized by the R.sub.50 (nm). The R.sub.50 (nm) is defined as the point at the long wavelength side of the blue emission peak were the intensity has dropped to 50% of the maximum intensity of the blue peak. The R.sub.50 (nm) for the different spectra is shown in FIG. 3 and in the below table.

(32) TABLE-US-00003 TABLE 1 PWL and R.sub.50 (nm) for the spectra shown in FIG. 3 PWL (nm) R.sub.50 (nm) 440 452 445 461 450 475 455 490

(33) The better white ‘rendering’ is also supported by FIG. 4. Besides a significant red shift (CIE u′) the color points also move further below BBL for spectra that use a shorter wavelength blue pump LED (or shorter R.sub.50). As a consequence, the color points for the samples with a short R.sub.50 are shifting significantly further below BBL (the distance to the BBL increases from ˜8 pts to ˜13 pts). This is perceived as much better (more preferred) white.

(34) The CIE v′ (calculated using the CIE 2006-10° observer) as a function of the R.sub.50 (nm) is shown in FIG. 5.

(35) IES TM30-15 was used to calculate the change in chroma induced by these sources. The change in chroma is plotted in a radar plot for the 16 different hue bins (FIG. 6) defined by IES TM30-15. Decreasing the R.sub.50 (nm) leads to an increase of the chroma (increasing saturation) for hue bins 4-7. The shape of the curve resembles the chroma changes observed for CDM-elite (often still referred to as the reference source). We found by preference testing that this gives a color perception close to CDM-elite.

(36) The proposed combination of spectral features leads to a preferred color rendering, combined with good white rendering with a small efficiency penalty and high color saturation index R.sub.g. GAI as defined in IES TM30-15 is herein also indicated as “R.sub.g”.

(37) In an example, GaYAG in combination with second orange or red phosphor and first red or orange phosphor (see above) was used. The latter two are a mixture of 2 red phosphors (SrAlSiN.sub.3:Eu (“orange”) and CaAlSiN.sub.3:Eu (“red”)).

(38) In another example, Intematix GAL540 in combination with second orange or red phosphor and first red or orange phosphor can be used. Very similar graphs as shown above can be obtained. There is however a small (but significant) shift in the R.sub.50 (nm) due to the change of the green phosphor as shown in FIG. 7. Visual judgement of the samples showed that the R.sub.50 (nm) should be below 462 nm, but more preferably even below 450 nm.

(39) A reference lamp indicates ad PW930 had the following values for white light generated therewith: R.sub.50=472, cie v′=0.511. Two alternative spectral distributions were created:

(40) R.sub.50=457 nm, preferred cie v′=0.508; and

(41) R.sub.50=450 nm, preferred cie v′=0.512.

(42) Some combinations were composed, as indicated in the table below:

(43) TABLE-US-00004 Orange Red Green/ luminescent luminescent Yellow material material (first (second (also second PWL luminescent luminescent luminescent R.sub.50 (nm) material) material) material) CRI R9 (nm) 440 GaYAG not available available 91 74 452 445 GaYAG available available 93 73 462 450 GaYAG available available 94 72 474 455 GaYAG available available 93 74 —

(44) The term “substantially” herein, such as in “substantially all light” or in “substantially consists”, will be understood by the person skilled in the art. The term “substantially” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term “substantially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term “comprise” includes also embodiments wherein the term “comprises” means “consists of”. The term “and/or” especially relates to one or more of the items mentioned before and after “and/or”. For instance, a phrase “item 1 and/or item 2” and similar phrases may relate to one or more of item 1 and item 2. The term “comprising” may in an embodiment refer to “consisting of” but may in another embodiment also refer to “containing at least the defined species and optionally one or more other species”.

(45) Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

(46) The devices herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

(47) It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “to comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

(48) The invention further applies to a device comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings.

(49) The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications. Below, some references in relation to the gamut area index (GAI or G.sub.a) are provided, which references are herein incorporated by reference.

REFERENCES FOR G.SUB.a

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