Lighting arrangement comprising an optical arrangement and an optical light guide

Abstract

A lighting arrangement (100), comprising a solid-state light source (110) arranged to emit blue light (120), an optical arrangement (130) comprising a light-converting element (140) arranged to receive the emitted blue light, wherein the light-converting element comprises a green-yellow phosphor (150) configured to convert a first part of the emitted blue light (120a) into green-yellow light (160) having a peak wavelength, λGY, in the range 510-580 nm, and an optical light guide (200), wherein the optical arrangement is configured to in-couple a second part of the emitted blue light (120b), and at least part of the green-yellow light, into the optical light guide, wherein the optical light guide comprises a red phosphor (210) configured to convert the in-coupled second part of the emitted blue light and / or the in-coupled green-yellow light into red light (220), and wherein the optical light guide is configured to out-couple the red and green-yellow light.

Description

[0001] LIGHTING ARRANGEMENT COMPRISING AN OPTICAL ARRANGEMENT AND AN

[0002] OPTICAL LIGHT GUIDE

[0003] FIELD OF THE INVENTION

[0004] The present invention generally relates to the field of lighting arrangements. More specifically, the present invention relates to a lighting arrangement comprising a solid- state light source, an optical arrangement and an optical light guide.

[0005] BACKGROUND OF THE INVENTION

[0006] Optical fibers are known in the art. US2018 / 0064322, for instance, describes an illumination system for a surgical device, the illumination system comprising: a tubular body made of a light permeable material, the tubular body comprising a peripheral wall, a distal end, a proximal end, and at least one lumen extending between the distal end and the proximal end, a light source that generates light having at least one wavelength between 200 nm and 2000 nm, and at least one light diffusing optical fiber disposed in the at least one lumen.

[0007] Recently, high-power white-light-emitting apparatuses including a combination of a laser diode (LD) and a phosphor have been developed. At present, white solid-state light sources mainly include a combination of a blue light emitting diode (LED) chip or a blue LD and a yellow phosphor.

[0008] WO2022 / 233618 discloses a high brightness light source comprising a blue laser pumping a green / yellow phosphor and a yellow / orange superluminescent diode pumping a red phosphor.

[0009] It should be noted that coupling laser light directly into an optical fiber has limitations with respect to safety issues and regulations, and this may further result in an undesired speckled light. Yet another issue is that systems of this kind may be relatively expensive.

[0010] Hence, it is of interest to provide a lighting arrangement or system which efficiently can provide (white) light, whilst fulfilling safety regulations and being cost- efficient. SUMMARY OF THE INVENTION

[0011] It is an object of the present invention to provide a lighting arrangement which is able to provide light, e.g. white light, whilst being safe and cost-efficient.

[0012] This and other objects are achieved by a lighting arrangement having the features in the independent claim. Preferred embodiments are defined in the dependent claims.

[0013] According to the present invention, there is provided a lighting arrangement. The lighting arrangement comprises a solid-state light source arranged to emit blue light having a peak wavelength, ZB, in a wavelength range of 400-500 nm, and an optical arrangement comprising a light-converting element arranged to receive the emitted blue light. The light-converting element comprises a green-yellow phosphor configured to convert a first part of the emitted blue light into green-yellow light having a peak wavelength, XGY, in a wavelength range of 510-580 nm. The lighting arrangement further comprises an optical light guide, wherein the optical arrangement is configured to in-couple a second part of the emitted blue light, and at least part of the green-yellow light, into the optical light guide. The optical light guide comprises a red phosphor configured to at least partly convert at least one of the in-coupled second part of the emitted blue light, and the in-coupled green-yellow light, into red light having a peak wavelength, R, in a wavelength range of 600-680 nm, wherein the optical light guide is configured to out-couple the red light and the green-yellow light.

[0014] The present invention is based on the idea of providing a lighting arrangement comprising a solid-state light source and an optical arrangement, wherein a green-yellow phosphor of the optical arrangement is provided to efficiently couple green-yellow converted light into an optical light guide comprising a red phosphor to convert blue light from the solid-state light source, and the green-yellow light converted light, into red converted light.

[0015] The present invention is advantageous in that the lighting arrangement is able to out-couple red light and green-yellow light in a convenient and easy manner, wherein the out-coupled red and green-yellow light may be used to obtain white light.

[0016] It will be appreciated that the green-yellow phosphor of the optical arrangement of the lighting arrangement affects the emitted blue light such that it loses its coherence and high intensity. By this conversion, the emitted blue light is not dangerous when exposed to human eyes, and the present invention is hereby advantageous in that it provides an increased safety compared to prior art arrangements. This conversion to less coherence and intensity is further advantageous for the red phosphor comprised by the light guide. Red phosphors pumped with high intensity light generally experience phenomena such as saturation (exceeding the maximum capacity of the phosphor to absorb and convert light), thermal quenching (heat generated by the light causes the phosphor to lose its ability to emit light efficiently), and degradation over time. Those effects may result in less efficiency, reduction in overall brightness and color quality (color shifting), shorter lifespan and reduced performance. These disadvantages of red phosphors are mitigated by the lighting arrangement of the present invention.

[0017] The present invention is further advantageous in that the lighting arrangement, by virtue of its components and construction, is cost-efficient.

[0018] The lighting arrangement comprises a solid-state light source. By “solid state light source”, it is here meant e.g. a laser light source, a plurality of laser diodes, a lightemitting diode, LED, light source, or a plurality of LEDs. The solid-state light source is arranged to emit blue light having a peak wavelength, ZB, in a wavelength range of 400-500 nm. The lighting arrangement further comprises an optical arrangement comprising a lightconverting element arranged to receive the emitted blue light. By “light-converting element”, it is here meant substantially any element arranged or configured to convert light which is directed towards the element. The light-converting element comprises a green-yellow phosphor configured to convert a first part of the emitted blue light into green-yellow light having a peak wavelength, XGY, in a wavelength range of 510-580 nm. Hence, a first part of the emitted blue light impingent on the light-converting element is converted into greenyellow light. The lighting arrangement further comprises an optical light guide. By “optical light guide”, it is here meant an optical element which is configured or arranged to guide light based on total internal reflection, TIR. The optical arrangement is configured to incouple a second part of the emitted blue light, and at least part of the green-yellow light, into the optical light guide. Hence, upon operation of the lighting arrangement, the second part of the emitted blue light, and the green-yellow light, are directed into the optical light guide, whereby the optical light guide in-couples the light. The optical light guide comprises a red phosphor configured to at least partly convert at least one of the in-coupled second part of the emitted blue light, and the in-coupled green-yellow light, into red light having a peak wavelength, R, in a wavelength range of 600-680 nm. Hence, the red phosphor is configured to at least partly convert the in-coupled second part of the emitted blue light and / or the incoupled green-yellow light, into red light having a peak wavelength, XR, in a wavelength range of 600-680 nm. The red phosphor may be distributed along at least a portion (of an elongation) of the optical light guide. The portion may preferably extend along more than 70%, more preferably more than 80%, most preferably more than 90% of the elongation or length of the optical light guide.

[0019] The optical light guide may further be configured to guide the in-coupled second part of the emitted blue light, and / or the in-coupled green-yellow light along at least the portion of the optical light guide.

[0020] The optical light guide is configured to out-couple the red light and the greenyellow light. Hence, the lighting arrangement is arranged or configured to out-couple the red light and green-yellow light from the optical light guide.

[0021] According to an embodiment of the present invention, the optical light guide may be further configured to out-couple at least a portion of the second part of the emitted blue light, wherein the out-coupled red light, the out-coupled green-yellow light, and the out- coupled at least a portion of the second part of the emitted blue light, is white light having a correlated color temperature, CCT, in a range from 1700K to 6500K and a color rendering index, CRI, of at least 70 or at least 80. Hence, the out-coupled (portion of the) second part of the emitted blue light, red light and green-yellow light, is white light with CCT=1700-6500 K and CRI > 80 (or CRI > 70). The present embodiment is advantageous in that the lighting arrangement is able to out-couple (obtain) white light in a safe, convenient and easy manner. The present embodiment is further advantageous in that the out-coupled / obtained white light of CRI > 80 is particularly suitable for illumination purposes and / or general lighting purposes.

[0022] According to an embodiment of the present invention, the solid-state light source may comprise a laser light source. The present embodiment is advantageous in that the laser maximizes light coupled into the optical light guide. The present embodiment is further advantageous in that the laser light source may pump the green-yellow phosphor at high intensity.

[0023] According to an embodiment of the present invention, the solid-state light source may comprise a light-emitting diode, LED, light source. The present embodiment is advantageous in that LEDs provide numerous advantages such as a long operational life, a low power consumption, and an efficient operation related to the ratio between light energy and heat energy.

[0024] According to an embodiment of the present invention, the optical light guide may be an optical fiber comprising a core and a cladding, wherein the cladding has a lower index of refraction than the core, and wherein the core is configured to guide the in-coupled green-yellow light and the second part of the emitted blue light based on total internal reflection, TIR. By the term “cladding”, it is here meant a lining, or the like, on the inside of the optical light guide, i.e. at the inside wall of the optical light guide, whereby the “core” constitutes a central portion of the optical light guide. The present embodiment is advantageous in that the ability of the core to guide the green-yellow light and the blue light based on TIR contributes even further to the efficiency of the lighting arrangement.

[0025] The cladding may comprise the red phosphor, or the optical light guide may further comprise a shell at least partly enclosing the cladding. The shell and / or the core may comprise the red phosphor.

[0026] Hence, the optical light guide may comprise a shell at least partly enclosing the cladding, wherein the shell comprises red phosphor, and / or that the cladding of the lighting arrangement comprises the red phosphor (i.e. without the presence of a shell). The present embodiment is advantageous in that the shell enclosing the cladding, or the cladding itself, of the optical light guide constitute(s) the optimal position(s) for the red phosphor, consequently leading to an even more efficient out-coupling of red light. More specifically, by the provision of the red phosphor in the shell and / or the cladding, the light guiding of the green-yellow light and the second portion of the blue light is not hindered, or at least only hindered to a minor extent.

[0027] According to an embodiment of the present invention, the optical light guide may comprise light out-coupling elements configured to couple one of the green-yellow light, and the green-yellow light and the portion of the second part of the emitted blue light out of the optical light guide. Hence, the light out-coupling elements may either couple the greenyellow light or the green-yellow light and the portion of the second part of the emitted blue light out of the optical light guide. By “light out-coupling elements”, it is here meant substantially any elements or particles arranged or configured to enhance, ameliorate and / or facilitate the out-coupling of the green-yellow light and / or the second part of the emitted blue light via e.g. scattering, redirection and / or conversion. The present embodiment is advantageous in that the light out-coupling elements achieve a particularly efficient extraction of the green-yellow light and / or the second part of the emitted blue light.

[0028] According to an embodiment of the present invention, the light out-coupling elements may comprise at least one of light scattering particles arranged to scatter impingent light, light directing structures arranged to redirect impingent light, and structures of the cladding. Hence, the light out-coupling elements may comprise light-scattering particles, light directing structures and / or the structures of the cladding. The present embodiment is advantageous in that properties such as scattering, (re)direction, etc., may even further ameliorate the light extraction of the lighting arrangement.

[0029] According to an embodiment of the present invention, the optical arrangement may further comprise a diffuser arranged upstream of said optical light guide. By “diffuser”, it is here meant substantially any element which is able, arranged or configured to diffuse light. The present embodiment is advantageous in that the diffuser may affect or influence the light such that the light loses its coherency, thereby conveniently increasing the safety of the lighting arrangement. Hence, the present embodiment is particularly advantageous in case of the use of a laser light source in the lighting arrangement.

[0030] According to an embodiment of the present invention, the optical arrangement may comprise at least one lens, and wherein the optical arrangement is configured to incouple the second part of the emitted blue light, and the green-yellow light, into the optical light guide via the at least one lens. The present embodiment is advantageous in that the lens(es) provide(s) an optimized in-coupling of the second part of the emitted blue light, and the green-yellow light, into the optical light guide.

[0031] According to an embodiment of the present invention, the red phosphor may be an organic red phosphor. The present embodiment is advantageous in that the organic red phosphor is inexpensive, thereby contributing to the cost-efficiency of the lighting arrangement.

[0032] According to an embodiment of the present invention, the red phosphor may be of a type M’xM2-2xAX6 doped with tetravalent manganese, wherein M’ comprises an alkaline earth cation, M comprises an alkaline cation, and x is in the range of 0-1, wherein A comprises a tetravalent cation, wherein X comprises a monovalent anion, at least comprising fluorine. With regard to Mn-activated narrow-band class red phosphors, this refers to a luminescent material of the type M’xM2-2xAX6 doped with tetravalent manganese, wherein M’ comprises an alkaline earth cation, M comprises an alkaline cation, and x is in the range of 0-1, wherein A comprises a tetravalent cation, for instance comprising one or more of silicon and titanium, wherein X comprises a monovalent anion, at least comprising fluorine. Relevant alkaline cations (M) are sodium (Na), potassium (K) and rubidium (Rb). Optionally, also lithium and / or cesium may be applied. In a preferred example, M comprises at least potassium. In yet another example, M comprises at least rubidium. The phrase “M comprises at least potassium” indicates for instance that of all M cations in a mole M’xM2-2xAX6 , a fraction comprises K+and an optionally remaining fraction comprises one or more other monovalent (alkaline) cations (see also below). In another preferred example, M comprises at least potassium and rubidium. Optionally, the M’xM2-2xAX6 has the hexagonal phase. In yet another example, the M’xM2-2xAX6 has the cubic phase. For x=0, the composition is M2AX6. Relevant alkaline earth cations (M’) are magnesium (Mg), strontium (Sr), calcium (Ca) and barium (Ba), especially one or more of Sr and Ba.

[0033] The term “tetravalent manganese” refers to Mn4+. This is a well-known luminescent ion. In the formula as indicated above, part of the tetravalent cation A (such as Si) is being replaced by manganese. Hence, M’xM2-2xAX6 doped with tetravalent manganese may also be indicated as M’xM2-2xAi-mMnmX6. The mole percentage of manganese, i.e. the percentage it replaces the tetravalent cation A will in general be in the range of 0.1-15 %, especially 1-12 %, i.e. m is in the range of 0.001-0.15, especially in the range of 0.01-0.12.

[0034] As indicated above, X relates to a monovalent anion, but at least comprises fluorine. Other monovalent anions that may optionally be present may be selected from the group consisting of chlorine (Cl), bromine (Br), and iodine (I).

[0035] It should be noted that this type or composition of red phosphor does not have self-absorption properties, and the present embodiment is hereby advantageous in that the red phosphor is particularly suitable for the optical light guide of the lighting arrangement. More specifically, the type or composition of red phosphor absorbs (almost) no green light and is thereby particularly suitable for the present invention.

[0036] According to an embodiment of the present invention, the red phosphor may be KSiF. According to an example, M’xM2-2xAX6 comprises BGSiFe (indicated herein also as KSiF system). As indicated above, in another preferred example, M’xM2-2xAX6 comprises KRbSiFe (herein also indicated as K,Rb system). As indicated above, part of silicon is replaced by manganese (i.e. the formula may also be described as K2Sii-mMnmF6 or KRbSii-mMnmF6, with m as indicated above, or as KRbSiFe:Mn and K2SiFe:Mn, respectively). As manganese replaces part of a host lattice ion and has a specific function, it is also indicated as “dopant” or “activator”. Hence, the hexafluorosilicate is doped or activated with manganese (Mn4+). The present embodiment is advantageous in that the composition of the red phosphor has optimum properties regarding non-self-absorption.

[0037] According to an embodiment of the present invention, wherein green-yellow phosphor is of a type AsBsOn Ce, wherein A comprises one or more of Y, La, Gd, Tb and Lu, and wherein B comprises one or more of Al, Ga, In and Sc. The present embodiment is advantageous in that this material composition of the green-yellow phosphor is able to be pumped by the solid-state light source (e.g. a (blue) laser light source) at a relatively high intensity, leading to the in-coupling of a relatively large amount of green-yellow light into the optical light guide. The embodiment with Ce doped garnet phosphor, in particular LuAG and cerium concentration in the range 0.4-1%, may be particularly advantageous. In this way, the thermal quenching is shifted to higher temperatures and photo saturation effects are minimized. Furthermore, laser light can be focused onto a small area for emitted light with a small etendue.

[0038] According to an embodiment of the present invention, there is provided a lighting unit. The lighting unit comprises a lighting arrangement according to any one of the preceding embodiments, and a housing arranged to at least partially enclose the solid-state light source and the optical arrangement. The present embodiment is advantageous in that the housing (e.g. in the form of a casing, or the like) provides an improved safety for the operator of the lighting arrangement and / or of any other third party (person). By the present embodiment, the laser class of the lighting arrangement may be lowered and may be used for business-to-consumer (B2C) markets.

[0039] Further objectives of, features of, and advantages with, the present invention will become apparent when studying the following detailed disclosure, the drawings, and the appended claims. Those skilled in the art will realize that different features of the present invention can be combined to create embodiments other than those described in the following.

[0040] BRIEF DESCRIPTION OF THE DRAWINGS

[0041] This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention.

[0042] Figs. 1 and 2 are schematic views of lighting arrangements according to exemplifying embodiments of the present invention,

[0043] Fig. 3 is a schematic view of an optical light guide of a lighting arrangement according to an exemplifying embodiment of the present invention,

[0044] Figs. 4a, 4b, 5a, 5b, 5c, 6a and 6b are schematic views of cross-sections of optical light guides of a lighting arrangement according to an exemplifying embodiment of the present invention,

[0045] Figs. 7a and 7b are schematic spectrum diagrams of power per wavelength, as a function of wavelength, of emitted white light from the lighting arrangement according to exemplifying embodiments of the present invention, and

[0046] Fig. 8 is a schematic view of a lighting unit comprising a lighting arrangement according to an exemplifying embodiment of the present invention. DETAILED DESCRIPTION

[0047] Fig. 1 is a schematic view of a lighting arrangement 100 according to an exemplifying embodiment of the present invention. The lighting arrangement 100 comprises a solid-state light source 110 which is schematically indicated by a dashed rectangle. The solid-state light source 110 may comprise a laser light source. The solid-state light source 110 may comprise a LED light source. The solid-state light source 110 is arranged to emit blue light 120 having a peak wavelength, B, in a wavelength range of 400-500 nm. For example, the solid-state light source 110 may be arranged to emit blue light 120 having a peak wavelength, B, in a wavelength range of 430-480 nm. The lighting arrangement 100 further comprises an optical arrangement 130. The optical arrangement 130 comprises a light-converting element 140. Here, the light-converting element 140 is exemplified as an oblong element, but it will be appreciated that many other forms or shapes of the lightconverting element 140 are feasible. The light-converting element 140 is arranged to receive the blue light 120 as emitted from the solid-state light source 110 upon operation of the lighting arrangement 100. The light-converting element 140 comprises a green-yellow phosphor 150. For example, the green-yellow phosphor 150 may be a garnet. The greenyellow phosphor 150 is configured to convert a first part of the emitted blue light 120 into green-yellow light 160 having a peak wavelength, XGY, in a wavelength range of 510-580 nm. For example, the green-yellow light 160 may have a peak wavelength, XGY, in a wavelength range of 520-560 nm. The lighting arrangement 100 further comprises an optical light guide 200, wherein the optical arrangement 130 is configured to in-couple a second part of the emitted blue light 120b, and at least part of the green-yellow light 160, into the optical light guide 200. According to the example of the lighting arrangement 100 of Fig. 1, the optical arrangement 130 comprises two lenses 400a, 400b on either side of the light-converting element 140. It should be noted that the lighting arrangement 100 may comprise a single lens (or alternatively, even no lens), that the lens(es) may have other shapes and / or positions that that shown, etc. According to the example of Fig. 1, comprising lenses 400a, 400b, the optical arrangement 130 is configured to in-couple the second part of the emitted blue light 120b, and at least part of the green-yellow light 160, into the optical light guide 200 via the lenses 400a, 400b.

[0048] The optical light guide 200 of the lighting arrangement 100, as exemplified in Fig. 1, extends along the main optical path of the second part of the emitted blue light 120b and / or the green-yellow light 160. The optical light guide 200 comprises a red phosphor 210 configured to at least partly convert the in-coupled second part of the emitted blue light 120b and / or the in-coupled green-yellow light 160, into red light 220 having a peak wavelength, XR, in a wavelength range of 600-680 nm. For example, the red light 220 may have a peak wavelength, XR, in a wavelength range of 610-650 nm. The optical light guide 200 is configured to out-couple the red light 220 and the green-yellow light 160, as indicated by (i) in Fig. 1. According to an example of the lighting arrangement 100 of the present invention, the optical light guide 200 may further be configured to out-couple at least a portion of the second part of the emitted blue light 120b. The out-coupled red light 220, the out-coupled green-yellow light 160, and the out-coupled at least a portion of the second part of the emitted blue light 120b, is white light, WL, as indicated by (ii) in Fig. 1. The white light, WL, has a correlated color temperature, CCT, in a range from 1700K to 6500K and a color rendering index, CRI, of at least 80.

[0049] Fig. 2 is a schematic view of a lighting arrangement 100 according to an exemplifying embodiment of the present invention. It will be appreciated that the lighting arrangement 100 in Fig. 2 shares the same concept as the lighting arrangement 100 shown in Fig. 1 and the associated text, and it is hereby referred also to Fig. 1 for an increased understanding of the lighting arrangement 100. In Fig. 2, the lighting arrangement 100 comprises two solid-state light sources 110 (e.g. laser light sources), arranged to emit blue light 120 having a peak wavelength, XB, in a wavelength range of 400-500 nm. The lighting arrangement 100 further comprises an optical arrangement 130, indicated by a dashed rectangle. The optical arrangement 130 comprises a light-converting element 140 arranged to receive the blue light 120 as emitted from the solid-state light sources 110 upon operation of the lighting arrangement 100. The light-converting element 140 comprises a green-yellow phosphor configured to convert a first part of the emitted blue light 120a into green-yellow light 160 having a peak wavelength, XGY, in a wavelength range of 510-580 nm.

[0050] The lighting arrangement 100 further comprises a diffuser 380, wherein the diffuser 380, in a transmissive mode, is arranged to diffuse the second part of the emitted blue light 120b. The second part of the emitted blue light 120b, and the green-yellow light 160, are in-coupled to an optical light guide 200 via reflectors 390. The optical light guide 200 comprises a red phosphor 210 configured to at least partly convert the second part of the emitted blue light 120b and / or the green-yellow light 160, into red light 220 having a peak wavelength, XR, in a wavelength range of 600-680 nm. The optical light guide 200 is configured to out-couple the red light 220 and the green-yellow light 160, as indicated by (i) in Fig. 2. Fig. 3 is a schematic view of an optical light guide 200 of a lighting arrangement according to an exemplifying embodiment of the present invention. The optical light guide 200 may be an optical fiber comprising a core 300 and a cladding 310 surrounding or enclosing the core 300. The cladding 310 is provided as a lining, or the like, on the inside of the optical light guide 200. The core 300 constitutes a central portion of the optical light guide 200. The cladding 310 may have a lower index of refraction than the core 300. The core 300 of the optical light guide 200 may be configured to guide the in-coupled green-yellow light 160 and the second part of the emitted blue light 120b based on total internal reflection, TIR, as schematically indicated by the dashed arrow. The optical light guide 200 may furthermore comprise a shell at least partly enclosing the cladding 310. The cladding 310, and / or the shell of the cladding 310, may comprise the red phosphor 210. The optical light guide 200 may comprise light out-coupling elements which are configured to couple either the green-yellow light 160 or the green-yellow light 160 and the portion of the second part of the emitted blue light 120b out of the optical light guide 200.

[0051] The red phosphor 210 may be an organic red phosphor. Furthermore, the red phosphor 210 may be of a type M’xM2-2xAX6 doped with tetraval ent manganese, wherein M’ comprises an alkaline earth cation, M comprises an alkaline cation, and x is in the range of 0- 1, wherein A comprises a tetraval ent cation, for instance comprising one or more of silicon and titanium, wherein X comprises a monovalent anion, at least comprising fluorine. Relevant alkaline cations (M) are sodium (Na), potassium (K) and rubidium (Rb). Optionally, also lithium and / or cesium may be applied. In a preferred embodiment, M comprises at least potassium. In yet another embodiment, M comprises at least rubidium. The phrase “wherein M comprises at least potassium” indicates for instance that of all M cations in a mole M’XM2- 2XAXe , a fraction comprises K+and an optionally remaining fraction comprises one or more other monovalent (alkaline) cations (see also below). In another preferred embodiment, M comprises at least potassium and rubidium. Optionally, the M’xM2-2xAX6 luminescent material has the hexagonal phase. In yet another embodiment, the M’xM2-2xAX6 luminescent material has the cubic phase. For x=0, the composition is M2AX6. Relevant alkaline earth cations (M’) are magnesium (Mg), strontium (Sr), calcium (Ca) and barium (Ba), especially one or more of Sr and Ba. The term “tetravalent manganese” refers to Mn4+. This is a well- known luminescent ion. In the formula as indicated above, part of the tetravalent cation A (such as Si) is being replaced by manganese. Hence, M’xM2-2xAX6 doped with tetravalent manganese may also be indicated as M’xM2-2xAi-mMnmX6. The mole percentage of manganese, i.e. the percentage it replaces the tetraval ent cation A will in general be in the range of 0.1-15 %, especially 1-12 %, i.e. m is in the range of 0.001-0.15, especially in the range of 0.01-0.12. As indicated above, X relates to a monovalent anion, but at least comprises fluorine. Other monovalent anions that may optionally be present may be selected from the group consisting of chlorine (Cl), bromine (Br), and iodine (I). In an embodiment, M’XM2-2XAX6 comprises K^SiFe (indicated herein also as KSiF system). As indicated above, in another preferred embodiment, M’xM2-2xAX6 comprises KRbSiFe (herein also indicated as K,Rb system). As indicated above, part of silicon is replaced by manganese (i.e. the formula may also be described as K2Sii-mMnmF6 or KRbSii-mMnmF6, with m as indicated above, or as KRbSiFe:Mn and K2SiFe:Mn, respectively). As manganese replaces part of a host lattice ion and has a specific function, it is also indicated as “dopant” or “activator”. Hence, the hexafluorosilicate is doped or activated with manganese (Mn4+). In specific embodiments, the luminescent material may comprise (K,Rb)2SiFe:Mn4+. Alternatively or additionally, in embodiments the third luminescent material may comprise K2SiFe:Mn4+. Alternatively or additionally, in embodiments the third luminescent material may comprise K2TiFe:Mn4+. In embodiments, the third luminescent material may comprise K2(Si,Ti)Fe:Mn4+. As can be derived from the above, “Si,Ti” may indicate one or more of Si and Ti.

[0052] The red phosphor 210 may for example be KSiF.

[0053] The green-yellow phosphor 150 may be of a type AsBsOn Ce, wherein A in embodiments comprises one or more of Y, La, Gd, Tb and Lu, especially (at least) one or more of Y, Gd, Tb and Lu, and wherein B in embodiments comprises one or more of Al, Ga, In and Sc. Especially, A may comprise one or more of Y, Gd and Lu, such as especially one or more of Y and Lu. Especially, B may comprise one or more of Al and Ga, more especially at least Al, such as essentially entirely Al. Hence, especially suitable luminescent materials are cerium comprising garnet materials. Embodiments of garnets especially include A3B5O12 garnets, wherein A comprises at least yttrium or lutetium and wherein B comprises at least aluminum. Such garnets may be doped with cerium (Ce), with praseodymium (Pr) or a combination of cerium and praseodymium; especially however with Ce. Especially, B may comprise aluminum (Al); however, in addition to aluminum, B may also partly comprise gallium (Ga) and / or scandium (Sc) and / or indium (In), especially up to about 20% of B, more especially up to about 10 % of B (i.e. the B ions essentially consist of 90 or more mole % of Al and 10 or less mole % of one or more of Ga, Sc and In); B may especially comprise up to about 10% gallium. In another variant, B and O may at least partly be replaced by Si and N. The element A may especially be selected from the group consisting of yttrium (Y), gadolinium (Gd), terbium (Tb) and lutetium (Lu). Further, Gd and / or Tb are especially only present up to an amount of about 20% of A. In a specific embodiment, the garnet luminescent material comprises (Yi-xLux)3B50i2:Ce, wherein x is equal to or larger than 0 and equal to or smaller than 1. The term “:Ce”, indicates that part of the metal ions (i.e. in the garnets: part of the “A” ions) in the luminescent material is replaced by Ce. For instance, in the case of (Yi-xLux)3A150i2:Ce, part of Y and / or Lu is replaced by Ce. This is known to the person skilled in the art. Ce will replace A in general for not more than 10%; in general, the Ce concentration will be in the range of 0.1 to 4%, especially 0.1 to 2% (relative to A). Assuming 1% Ce and 10% Y, the full correct formula could be (Yo.iLuo.sgCeo.o sALOn. Ce in garnets is substantially or only in the trivalent state, as is known to the person skilled in the art.

[0054] The organic red phosphor is typically molecularly dissolved in a matrix e.g. a polymer matrix e.g. of PMMA or PC or PET.

[0055] Figs. 4a and 4b are schematic views of cross-sections of an optical light guide 200 of a lighting arrangement according to an exemplifying embodiment of the present invention, and it may be referred to Figs. 1-3 for an increased understanding of the optical light guide 200 of the lighting arrangement 100. In Fig. 4a, the core 300 of the optical light guide 200 comprises (schematically indicated) phosphor particles 340. The phosphor particles 340 may be arranged to convert impingent light (exemplified by 340a, and furthermore indicated by the asterisk “*”), whereas the schematically indicated phosphor particles 340b, 340c, are arranged to scatter impingent light (indicated by the symbol “A”). Hence, the phosphor particles 340 in Fig. 4a may convert light (to a larger extent) or scatter (to a lesser extent) impingent light. In Fig. 4b, the core 300 of the optical light guide 200 comprises (schematically indicated) phosphor particle 340d arranged to convert impingent light, and light out-coupling elements 350, wherein the light out-coupling elements 350 are exemplified as two light-scattering elements 350a, 350b, arranged to scatter impingent light.

[0056] Figs. 5a-c are schematic views of cross-sections of an optical light guide 200 of a lighting arrangement according to an exemplifying embodiment of the present invention. The optical light guide 200 comprises a cladding 310 surrounding the core 300 of the optical light guide 200. In Fig. 5a, phosphor particles 340 are provided in the cladding 310, wherein the phosphor particles 340 are arranged to convert or scatter impingent light. In Fig. 5b, phosphor particles are arranged in the cladding 310 of the optical light guide 200, whereas light out-coupling elements 350a-c in the form of (non-luminescent) light-scattering elements arranged to convert or scatter impingent light are provided in the core 300 of the optical light guide 200. In Fig. 5c, (all) particles, comprising both phosphor particles and light-scattering elements, are provided in the cladding 310 of the optical light guide 200. Figs. 6a and 6b are schematic views of cross-sections of an optical light guide 200 of a lighting arrangement according to an exemplifying embodiment of the present invention. The optical light guide 200 comprises a shell 330 at least partly enclosing the cladding 310, which in turn at least partly encloses the core 300. Phosphor particles 340 are arranged in the shell 330 of the optical light guide 200. Light out-coupling elements 350 in the form of light-scattering particles, arranged to scatter impingent light, are arranged in the cladding 310 of the optical light guide 200. The optical light guide 200 in Fig. 6a further comprises schematically indicated structures in the cladding 310, wherein these structures may be examples of light out-coupling elements 350. The structures may comprise an element 360a, as indicated in the left-hand side of Fig. 6a. Alternatively, the structures may comprise or constitute a damage, (irregularity) pattern, or the like, of the cladding 310, as indicated by 360b in the right-hand side of Fig. 6a. Fig. 6b shows an example of light out- coupling elements 350 being arranged at the interface between the core and the cladding of the optical light guide 200, whereby this arrangement of the light out-coupling elements 350 enhances the light extraction of the optical light guide 200.

[0057] It should further be noted that for the optical light guides 200 as exemplified in Figs. 4-6, a bending of the optical light guide 200 may result in (further) light outcoupling.

[0058] Figs. 7a and 7b are schematic spectrum diagrams of power per wavelength, as a function of wavelength, of emitted white light from the lighting arrangement according to exemplifying embodiments of the present invention. The green-yellow phosphor of the lightconverting element of the optical arrangement of the lighting arrangement is of type LuAG with 0.5% Ce and lumogen red emission. In Fig. 7a, the spectrum is shown at CCT = 3000K and CRI = 87, comprising a significant peak at wavelengths of approximately 600 nm. In Fig. 7b, the spectrum is shown at CCT = 4000K and CRI = 90, comprising a significant peak at wavelengths of approximately 460 nm and a significant peak at wavelengths of approximately 600 nm.

[0059] Fig. 8 is a schematic view of a lighting unit 500 comprising a lighting arrangement 100 according to an exemplifying embodiment of the present invention. The lighting unit 500 further comprises a housing 510, e.g. in the form of a casing, or the like, which is provided or arranged to at least partially enclose the solid-state light source 110 (schematically indicated by a dashed oval) and the optical arrangement 130 (schematically indicated by a dashed oval).

[0060] The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, the optical arrangement 130, the optical light guide 200, etc., may have different shapes, dimensions and / or sizes than those depicted / described.

Claims

CLAIMS:

1. A lighting arrangement (100), comprising a solid-state light source (110) arranged to emit blue light (120) having a peak wavelength, B, in a wavelength range of 400-500 nm, an optical arrangement (130) comprising a light-converting element (140) arranged to receive the emitted blue light, wherein the light-converting element comprises a green-yellow phosphor (150) configured to convert a first part of the emitted blue light (120a) into green-yellow light (160) having a peak wavelength, XGY, in a wavelength range of 510-580 nm, and an optical light guide (200), wherein the optical arrangement is configured to in-couple a second part of the emitted blue light (120b), and at least part of the green-yellow light, into the optical light guide, wherein the optical light guide comprises a red phosphor (210) configured to at least partly convert at least one of the in-coupled second part of the emitted blue light, and the in-coupled green-yellow light, into red light (220) having a peak wavelength, R, in a wavelength range of 600-680 nm, and wherein the optical light guide is configured to out-couple the red light and the green-yellow light.

2. The lighting arrangement according to claim 1, wherein the optical light guide is further configured to out-couple at least a portion of the second part of the emitted blue light, wherein the out-coupled red light, the out-coupled green-yellow light, and the out-coupled at least a portion of the second part of the emitted blue light, is white light, WL, having a correlated color temperature, CCT, in a range from 1700K to 6500K and a color rendering index, CRI, of at least 80.

3. The lighting arrangement according to claim 1 or 2, wherein the solid-state light source comprises a laser light source.

4. The lighting arrangement according to any one of the preceding claims, wherein the solid-state light source comprises a light-emitting diode, LED, light source.

5. The lighting arrangement according to any one of the preceding claims, wherein the optical light guide is an optical fiber comprising a core (300) and a cladding (310), wherein the cladding has a lower index of refraction than the core, and wherein the core is configured to guide the in-coupled green-yellow light and the second part of the emitted blue light based on total internal reflection, TIR.

6. The lighting arrangement according to claim 5, wherein(i) the cladding (310) comprises the red phosphor, or(ii) the optical light guide further comprises a shell (330) at least partly enclosing the cladding, wherein the shell and / or the core comprises the red phosphor (340).

7. The lighting arrangement according to any one of the preceding claims, wherein the optical light guide comprises light out-coupling elements (350) configured to couple one of the green-yellow light, and the green-yellow light and the portion of the second part of the emitted blue light, out of the optical light guide.

8. The lighting arrangement according to claim 7, wherein the light out-coupling elements comprises at least one of light scattering particles (350) arranged to scatter impingent light, light redirecting structures arranged to redirect impingent light, and structures (360) of the cladding.

9. The lighting arrangement according to any one of the preceding claims, wherein the optical arrangement further comprises a diffuser (380) arranged upstream of the optical light guide.

10. The lighting arrangement according to any one of the preceding claims, wherein the optical arrangement comprises at least one lens (400a, 400b), and wherein the optical arrangement is configured to in-couple the second part of the emitted blue light, and the green-yellow light, into the optical light guide via the at least one lens.

11. The lighting arrangement according to any one of the preceding claims, wherein the red phosphor is an organic red phosphor.

12. The lighting arrangement according to any one of the preceding claims, wherein the red phosphor is of a type M’xM2-2xAX6 doped with tetravalent manganese, wherein M’ comprises an alkaline earth cation, M comprises an alkaline cation, and x is in the range of 0-1, wherein A comprises a tetravalent cation, wherein X comprises a monovalent anion, at least comprising fluorine.

13. The lighting arrangement according to claim 12, wherein the red phosphor is KSiF.

14. The lighting arrangement according to any one of the preceding claims, wherein green-yellow phosphor is of a type AsBsOn Ce, wherein A comprises one or more of Y, La, Gd, Tb and Lu, and wherein B comprises one or more of Al, Ga, In and Sc.

15. A lighting unit (500), comprising the lighting arrangement according to any one of the preceding claims, and a housing (510) arranged to at least partially enclose the solid-state light source and the optical arrangement.

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