Light emitting device with cooling system - Patents.com

Abstract

A light emitting device 1 comprising: a plurality of light emitting diodes LED configured to emit incident light Ld; a light emitting diode having a refractive index n including two parallel faces along a horizontal plane xy called a first large face FE1 and a second large face FE2, and faces with n ∈ N > 2 called side faces FL1, FL2, FL3, FL4. c a solid-state light-emitting collector CL, wherein at least one of the first large surface and the second large surface is illuminated by the incident light Ld, and the collector absorbs the incident light Ld and then emits luminescent light L L a portion of the luminescence light is guided by total internal reflection Lg within the light collector and has a refractive index n s <n c The exit beam L passes through a so-called first exit surface of the light collector FL1, which is in contact with the exit medium EM. s a so-called cooling system CS comprising a coolant CM in contact with at least one of the faces of said collector, referred to as cooled face FE1, said cooling system being adapted to remove at least a portion of the heat generated in said collector by said plurality of light emitting diodes, said coolant having a refractive index n ext is n c >n ext >1 and matched to the refractive index of the exit medium and the refractive index of the collector to limit losses in light extraction efficiency of the exit beam induced by the coolant.

Description

[Technical field]

[0001] The present invention relates to the field of luminescent collectors, and more particularly to collectors equipped with a cooling system. [Background technology]

[0002] Light emitting diodes (LEDs) have many applications in the field of lighting. However, the brightness of LEDs is limited to values ​​that make them unsuitable for some applications.

[0003] One solution to increase the brightness of LEDs is to use LED-excited luminescent concentrators (see, for example, Non-Patent Document 1). These concentrators are crystals that fluoresce in the visible (red-orange) range, such as Ce:YAG, which absorbs in the blue range (about 450 nm) at wavelengths where LEDs are very efficient. The crystals are cut in the form of planes and lined with hundreds (even thousands) of LEDs on both large faces, emitting at the edges. These concentrators can achieve brightness values ​​10-20 times higher than those of LEDs.

[0004] FIG. 1A shows an example of a light emitting module ME0 known in the prior art, based on a collector crystal CL. FIG. 1A shows a schematic perspective view of the light emitting module ME0. The light emitting module ME0 comprises a set of LEDs emitting in a first spectral band and a collector CL. The collector CL is a fluorescent parallelepiped crystal having at least one illumination surface SI1, SI2 of dimensions L×w, which is illuminated by the electroluminescent radiation Ld emitted by the LEDs. The illumination surfaces SI1, SI2 are also called "major surfaces". The other four surfaces are called side surfaces.

[0005] The collector crystal is configured to absorb electroluminescent radiation Ld. The luminous flux emitted by the LED and directed towards the illumination surface is absorbed by the luminophores Lum of the fluorescent crystal. These are distributed throughout the volume of the crystal and then emit fluorescent radiation inside the crystal. The emitted rays of fluorescent radiation can be divided into two main categories: -Trapped rays, called Lp: These rays are trapped inside the crystal due to total internal reflection (TIR) ​​on the various faces of the crystal. These rays exist if the crystal is a parallelepiped with six faces, two of which are parallel. The trapped rays never leave the crystal; - Untrapped rays are rays that finally exit the crystal. They are divided into two subcategories: guided rays Lg, which are guided to TIR on the faces of the collector and then emerge on one of the faces of the collector, and unguided rays L, which emerge directly from the collector without being reflected on the faces. out The light rays passing through the side surface SE are divided into the output beam L s Form.

[0006] FIG. 1B shows the escape cone L using angular coordinates (α, β) in the xyz coordinate system. g and L out where β is the angle with respect to the Oz axis and α is the angle in the xy plane with respect to the Ox axis. The brighter areas between the cones are the captured rays L p This figure is given by way of example for the prior art crystal of FIG. 1A, with diamond crystal (refractive index n=2.4). Assuming that the surrounding medium is air and considering the Snell-Descartes law, for diamond the critical angle is θ c = 24.6°. From Fig. 1B, the light ray L guided by the TIR escapes through the four sides. g Four escape cones corresponding to the corners of the exit beam L can be seen. s The escape cone corresponding to the rays forming is the second one from the left. The percentage of radiation captured by the TIR compared to the uncaptured radiation is determined by the refractive index of the crystal and that of the surrounding medium by the Snell-Descartes law. For a parallelepiped collector made from diamond (n=2.4) in surrounding air, the percentage of captured rays is 73%.

[0007] In a collector crystal, the power of the output beam can be increased by increasing the pump power. However, the pump power is limited by the difficulty of cooling the collector. Total internal reflection (TIR) ​​on the guiding surface is very sensitive to contact with materials with a higher refractive index than air. TIR is very easily blocked, inducing light leakage from surfaces other than the output surface, which reduces the power of the output beam L. s The light extraction efficiency of the LEDs may be reduced. A first strategy to limit this problem is to operate the pump LEDs in quasi-continuous wave mode: the peak power can be increased while the average pump power is kept at a low level compatible with passive cooling of the collector (Non-Patent Document 2).

[0008] For high average pump powers in quasi-continuous or continuous wave operation, the simplest solution is to cool the collector with air (Non-Patent Document 3). In Non-Patent Document 4, the collector is cooled using two copper blocks, while avoiding optical contact with the collector. In Non-Patent Document 5, the collector is cooled by mechanical contact in the form of a tip on the two largest sides of the collector. The sides are less stressed by total internal reflection, so it is not contradicted by the extremely low contact-induced losses (published losses are 1%-2%). However, it should be noted that the pump power used in this setup remains moderate and the cooling capacity of the setup is low. Similarly, Patent Document 1 features cooling by mechanical parts placed close to the collector (within "30 μm" on the hub and within "10 μm but not less than 1 μm" on the output guide).

[0009] However, all of these methods are very inefficient at removing heat from the crystal and are not compatible with large input powers (e.g., pumping the crystal with thousands of LEDs, each emitting at watt levels).

[0010] To avoid blocking of total internal reflection, one solution is to place a mirror on the guide surface of the collector. As a result, contact cooling is possible behind the reflecting surface without changing the reflectivity of the surface. For example, in [6], a large surface of a Ce:YAG collector is covered with a dielectric mirror and in contact with a copper radiator, using this type of cooling. The reflectivity obtained by this treatment is less efficient than total internal reflection. For an exit surface in air, the induced losses are moderate (6%). This method makes it possible to limit the heating of the Ce:YAG to a temperature difference of 10° for a pump power of 22 W, while the temperature rise reaches 90° when the crystal is not cooled. However, the large surface covered by the mirror is functionalized only to cool and guide the emitted beam. The possibility of pumping this functionalized surface is eliminated, resulting in a 50% reduction in the potential pump power. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Canadian Patent No. 2929118 [Non-patent literature]

[0012] [Non-Patent Document 1] Barbet, Adrien, et al. “Light-emitting diode pumped luminescent concentrators: a new opportunity for low-cost solid-state lasers.”, Optica3.5(2016):465-468. [Non-Patent Document 2] A. BARBET, et al. “LED pumped luminescent concentrators: a new opportunity for low cost solid-state lasers” Optica, Vol. 3, No 5, pp. 465-468 (April 2016) [Non-Patent Document 3] DKGde Boer,et al.High-brightness source based on luminescent concentration,Optics Express,vol.24,no.14,page A1069,July 2016. [Non-Patent Document 4] Sathian, J. et al. “Solid-state source of intense yellow light based on a Ce:YAG luminescent concentrator”, Optics Express, vol. 25, no. 12, page 13714, June 2017 [Non-Patent Document 5] Christoph Hoelen, et al. “Progress in extremely high brightness LED-based light sources”, Sixteenth International Conference on Solid State Lighting and LED-based Illumination Systems, Proc. of SPIE Vol.10378,103780N [Non-Patent Document 6] Juna Sathian, et al. “Enhancing Performance of Ce:YAG Luminescent Concentrators for High Power Applications” CLEO Europe 2019 paper CD'-P.2(2019)

[0013] The present invention aims to alleviate certain problems of the prior art. To this end, the subject of the invention is a light-emitting device comprising a solid parallelepiped light-emitting crystal excited by a plurality of light-emitting diodes, one of the faces of said collector being in contact with a coolant adapted to remove at least a portion of the heat generated in said collector by said plurality of light-emitting diodes, said coolant having a refractive index n ext>1 is a light emitting device in which the refractive index of the output medium and the refractive index of the collector are matched to limit the loss of light extraction efficiency of the output beam induced by the coolant. Thus, in the present invention, crystals can be efficiently cooled by optical contact with a coolant with a controlled refractive index without affecting or with minimal effect on the light extraction efficiency of the collector. Summary of the Invention

[0014] To this end, the subject of the invention is a light-emitting device comprising: - a plurality of light emitting diodes configured to emit incident light; - Two parallel planes along the horizontal plane xy called the first and second major faces, and two parallel planes called the side faces

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[0015] Refractive index n including the surface c wherein at least one of the first and second major surfaces is illuminated by the incident light, the collector configured to absorb the incident light and then emit luminescent light, a portion of the luminescent light being guided by total internal reflection (Lg) within the collector and having a refractive index n s <n c a solid-state light-emitting collector, the solid-state light-emitting collector passing through a so-called first exit surface of the collector in contact with the exit medium of the solid-state light-emitting collector to form an exit beam; a so-called cooling system comprising a coolant in contact with at least one of the faces of a collector, called the cooled face, said cooling system adapted to remove at least a part of the heat generated in said collector by said plurality of light-emitting diodes, said coolant having a refractive index n ext is n c >n ext >1 and matched to the refractive index of the exit medium and the refractive index of the collector to limit losses in light extraction efficiency of the exit beam induced by the coolant.

[0016] In a preferred embodiment of the invention, the refractive index of the refrigerant is such that the loss in light extraction efficiency of the outgoing beam is 15% or less.

[0017] In a preferred embodiment of the present invention, the refractive index of the refrigerant is

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[0018] It is.

[0019] In a preferred embodiment of the invention, the coolant is in contact with at least 90% of said cooled surface.

[0020] In one variant of the invention, the coolant is in contact with the first and second large surfaces.

[0021] In one embodiment of the invention, the cooling system comprises a layer in a thermally conductive material that conducts heat to a mechanical radiator, said layer forming a coolant.

[0022] In one embodiment of the present invention, the refrigerant is water.

[0023] In one embodiment of the present invention, the cooling system comprises a holder adapted to support a light collector and a plurality of light emitting diodes, and a flow path connected to a water source, the flow path being adapted to transport said water, and the holder comprising a sealing element adapted to ensure sealing of the device.

[0024] In a preferred embodiment of the invention, the device comprises a mirror covering the face opposite the exit face of the collector.

[0025] In one embodiment of the invention, the device comprises an additional solid-state luminescent collector, wherein the emission beam excites said additional collector via a so-called receiving surface of said additional collector in contact with an emission medium, said additional collector being adapted to absorb said emission beam and then emit additional luminescence radiation, a part of said additional luminescence radiation passing through a so-called additional exit surface of said additional collector and forming an emission beam, said additional exit surface having a refractive index n' s and an additional exit medium having a refractive index n s is the refractive index of the additional concentrator and the refractive index of the additional exit medium n' s , thereby achieving the highest extraction efficiency of said additional output beam. [Brief description of the drawings]

[0026] Other characteristics, details and advantages of the invention will become apparent from the description made with reference to the attached drawings, given by way of example and respectively illustrating:

[0027] [Figure 1A] FIG. 1A shows a light-emitting module known from the prior art, which is based on a light-collecting crystal. [Figure 1B] FIG. 1B is a plan view of escape cones Lg and Lout of a prior art light emitting module. [Figure 2A] FIG. 2A shows a light emitting device according to the present invention. [Figure 2B] FIG. 2B is a diagram of escape cones associated with rays Lg, Ls, Lout,1 and Lout,2 of a light emitting device according to the present invention. [Figure 2C] FIG. 2C is a plan view of the escape cones of rays Lg, Ls, Lout,1 and Lout,2 of a device according to a second embodiment. [Figure 2D] FIG. 2D is a plan view of the escape cones of rays Lg, Ls, Lout,1 and Lout,2 of a device according to a third embodiment. [Figure 3A] FIG. 3A shows a light emitting device according to a modified example of the present invention. [Figure 3B] FIG. 3B shows a plan view of the escape cones of the rays Lg, Ls, Lout,1 and Lout,2 of a device according to a variant of the invention. [Figure 4] FIG. 4 is a plan view of the escape cones of rays Lg, Ls, Lout,1 and Lout,2 of a device according to a fourth embodiment. [Diagram 5] FIG. 5 is a plan view of the escape cones of rays Lg, Ls, Lout,1 and Lout,2 of a device according to this embodiment. [Figure 6A] FIG. 6A is a perspective view of a light emitting device according to another embodiment of the present invention. [Figure 6B] FIG. 6B is a side view of a light emitting device according to another embodiment of the present invention, taken along cross section AB. [Figure 6C] FIG. 6C is a side view of a light emitting device according to another embodiment of the present invention, taken along cross section CD. [Figure 7] FIG. 7 shows a light emitting device according to another embodiment of the present invention. [Figure 8] FIG. 8 shows a light emitting device according to another embodiment of the present invention, comprising a cascade of two luminescent collectors CL, CL'.

[0028] In the drawings, elements are not drawn to scale unless specifically noted. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Figure 2A shows a light emitting device 1 according to the invention. The device 1 of the invention comprises a number of light emitting diodes LED arranged to emit incident light Ld.

[0030] In order to increase the brightness of the light emitting diode LED, the device of the invention has two parallel faces, called first and second large faces FE1, FE2, along a horizontal plane xy, and two parallel faces, called side faces FL1, FL2, FL3, FL4, along a horizontal plane xy.

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[0031] 2A, the light collector CL has a refractive index n c and a surface of n = 1. As an illustrative example of FIG. 2A, the light collector CL is a rectangular parallelepiped having a thickness e and has first and second large faces FE1, FE2 of dimensions L×w in a horizontal plane xy.

[0032] The light emitting diode LED excites the light collector CL through at least one of the first and second large faces illuminated by incident light Ld, which is distributed throughout the volume of the crystal and generates luminescence light Ld inside the crystal. L is absorbed by the luminophore Lum of the luminescence collector CL which emits

[0033] According to one embodiment, the light collector is a crystal, such as Ce:YAG or Ce:LYSO. In another embodiment, the light collector is not a crystal but another material, such as glass or PMMA doped with a luminophore.

[0034] As known to those skilled in the art, a portion of the luminescence light, called the captured portion Lp, is captured by total internal reflection within the collector. As mentioned above, the ratio of captured and uncaptured rays is determined by the refractive index of the collector and the refractive index of the surrounding medium by the Snell-Descartes law. The captured rays are denoted Lp and cannot leave the collector due to TIR on the various faces of the collector. The uncaptured rays are the rays that ultimately leave the collector. They are divided into two subcategories: guided rays Lg, which are guided by TIR on the main or side faces and emerge on one of the faces of the collector, and unguided rays L, which emerge directly from the faces FE1 and FE2 of the collector, respectively, without being reflected on the faces. out,1 and L out,2 It can be divided into:

[0035] Guiding ray L g Part L s is the refractive index n s <n c EM, and passes through a first so-called exit surface FL1 of the collector, which is in contact with the exit medium EM ofs 2A, given as an illustrative example, the exit face FL1 has dimensions e×w. In another embodiment, the exit face is formed by another side, for example a side FL2, having dimensions L×w.

[0036] According to one embodiment of the present invention, the exit medium is air (see, for example, FIG. 2B). In another embodiment, in order to increase the light extraction efficiency of the exit beam, the exit medium is n s >1 (see, for example, FIG. 2C).

[0037] The device of the invention comprises a so-called cooling system CS, which comprises a coolant CM in contact with at least one of the faces of the collector (hereafter called "cooled face"). The cooling system is adapted to remove at least a part of the heat generated in the collector CL by the plurality of light emitting diodes LED. The refractive index of the coolant n ext is set to n to allow for a higher thermal conductivity than air. c >n ext >1. Unlike prior art light emitting devices, the coolant is in uniform contact with most of the surface of the cooled surface FE1. More precisely, the coolant is in contact with more than 90% of the cooled surface. This allows for much more efficient cooling of the excitation power compared to prior art configurations using only a single contact point with the cooled surface. As an illustrative example, in FIG. 2A, the only cooled surface is the large surface FE1. In another embodiment of the invention, more faces of the light collector CL, for example FE1 and FE2 (see, for example, FIG. 3A), or FE1, FE2, FL2 and FL4 (see, for example, FIG. 6A-6C), are in contact with the coolant in order to increase the heat removed by the cooling system. Thus, more LEDs and a larger excitation power can be used.

[0038] The cooling system CS cools the light L that is guided into the light collector and passes through the exit surface FE1. s More precisely, the refractive index of the refrigerant C M is n ext is the exit beam L guided by the refrigerant CM sIn order to limit the loss of light extraction efficiency of the exit medium n s Refractive index and concentrator n c In fact, as mentioned above, the total internal reflection on the guiding surface of the collector CL is very sensitive to contact with a material with a higher refractive index than air. Therefore, n ext Unless carefully selected, the presence of coolant in contact with the cooled surface FE1 will induce significant light leakage from surfaces other than the exit surface, resulting in the exit beam L s This may reduce the light extraction efficiency.

[0039] Preferably, the refractive index of the coolant is such that it does not induce a loss in the light extraction efficiency of the outgoing beam (see, for example, FIGS. 2B to 4).

[0040] In the embodiment shown in Fig. 2A, the face of the light collector excited by the diode LED is the same as the face in contact with the coolant FE1. Therefore, in this embodiment, the coolant CM needs to be transparent to the incident light emitted by the LED. More generally, when the coolant covers the face excited by the LED, the cooling is transparent to the light emitted by the LED.

[0041] To better understand the effect of the cooling medium on the extraction efficiency, FIG. 2B shows the extraction efficiency of the ray L using the angular coordinates (α, β) in the xyz coordinate system of FIG. 2A. g , L s , L out,1 and L out,2 The lighter areas between the cones are the capture rays L p is equivalent to.

[0042] As an example, the diagram of FIG. 2B is shown in FIG. 2A with the refractive index n ext Coolant and ejection medium n = 1.5 s = 1 (air). Thus, all surfaces other than the surface to be cooled are in the surrounding air. This embodiment of the invention will be referred to as the first embodiment M1. For example, the collector CL has a refractive index n c= 1.83 Ce:YAG crystal.

[0043] The escape cones in FIG. 2B, designated 0°, 180°, and 270°, have guided rays L exiting from sides FL2, FL4, and FL3, respectively. g θ c,g are called the critical angles of these escape cones. The rays L that form the exit beam s The escape cone associated with is shown as 90° in FIG. c,s is called the critical angle of this escape cone. Considering the refractive indices and geometry of this embodiment M1, the critical angles of TIR on the surfaces FL1, FL2, FL3, FL4 and FE2 of the collector in contact with air are c,g =θ c,s =sin-1(n s / n c )=sin-1(1 / 1.83)=33°. Rays propagating in the collector CL at angles equal to or greater than the critical angle with respect to the normal of their faces are trapped within the collector CL. As can be seen from FIG. 2B, the ray L associated with the cooled face FE1 out,1 The critical angle θ of the escape cone c,out1 =sin-1(n ext / n c )=55° is the ray L associated with the large surface FE2 out,2 The critical angle θ of the escape cone c,out2 =θ c,g = 33°. This is because the refractive index n ext n c >n ext >1 and is therefore greater than the refractive index of air, which is the medium in contact with the surface FE2.

[0044] In addition, the refrigerant CM is emitted beam L s In order to ensure that no loss of light extraction efficiency occurs, the light ray L out,1 The range of angles and the ray L s In the configuration shown in FIG. 2B, taking into account the Snell-Descartes law, there is no overlap as long as the following is satisfied: [Number]

[0045] In embodiment M1, θ c,s = 33° and n c = 1.83, this means that n ext As long as n satisfies ≦1.53, it means that there is no overlap. ext = 1.5, so ray L out,1 The range of angles and the ray L s There is no overlap between the angular ranges of

[0046] EQ0 is the output beam L s This suggests that it is possible to use water as a refrigerant without inducing a loss in the light extraction efficiency of . That is, in one embodiment, the refrigerant is water (n ext = 1.333), the light collector is Ce:YAG, and all surfaces other than the cooled surface FE1 are in contact with air. In this embodiment, the coolant CM is n ext ≦1.53, so the output beam L s Also for this embodiment, the percentage of luminescent light exiting the exit face FL1 (i.e., the light extraction efficiency) is 8% of the total luminescent light emitted by the collector.

[0047] The use of water to cool the light collector CL is advantageous since this type of cooling can be shared with the LEDs. Indeed, the efficiency of LEDs is about 30%, so they need to evacuate most of their power (at the kW level if several thousand LEDs are used). Thus, in a preferred embodiment of the invention, the number of light emitting diodes LEDs exciting the light collector CL contained in the device 1 is more than 1000, the coolant is water and the cooling system is adapted to cool both the light collector CL and the LEDs with said water.

[0048] Thus, the device of the present invention emits an output beam L sIn order to efficiently remove the heat generated in the light collector CL by the LEDs without causing a loss in the light extraction efficiency, a coolant (such as water) with a higher thermal conductivity than air can be used.

[0049] In the embodiment shown in FIG. 2A, only the large surface FE1 is excited. In another embodiment, a higher excitation power, i.e. a higher power output beam L s To achieve this, both large faces FE1 and FE2 are excited by LEDs.

[0050] In order to achieve a higher light extraction efficiency of the output beam, in a second embodiment M2 of the present invention, the output medium has a refractive index n higher than that of air. s (n s >1), and the refractive index of the refrigerant, n ext is equal to (n s =n ext ) For example, the exit medium may be glue or water. FIG. 2C shows the ray L of the second embodiment M2 with the same angular coordinates (α, β) as FIG. 2B. g , L s , L out,1 and L out,2 2C shows a plan view of an escape cone having a refractive index n c The refractive index is given for the light collector of the present invention shown in FIG. 2A, which has a Ce:YAG crystal with refractive index n = 1.83. The other surfaces than the cooled surface and the exit surface are in air. c When L is as small as possible, s To achieve the highest loss-free extraction efficiency of the beam, it is necessary to satisfy the following equation:

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[0051] No loss means that the light ray L passes through the cooled surface or a surface other than the exit surface before passing through the exit surface FL1. s This means that there is no light leakage of θ c,s =θ c,out1 = 45°, so the light ray L emitted from the cooled surface FE1out,1 The range of angles and the light ray L exiting from the exit surface FL1 s This is because there is no overlap between the range of angles of the refrigerant and the refractive index n s Using an extraction medium having a .mu.m diameter, the light extraction efficiency of the output beam was increased from 8% in embodiment M1 to 14.5% in embodiment M2 while maintaining lossless extraction.

[0052] In the third embodiment M3, the ejection medium is a refrigerant having a refractive index n ext Different refractive index n s (n s ≠ n ext ), which means that n s >n ext By using s =n ext The embodiment M2 has a higher exit beam L s Alternatively, it may be advantageous to use a particular refrigerant (e.g., water) that is not suitable for the emission medium. s To guarantee lossless extraction efficiency for the output medium, the following condition is required:

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[0053] Furthermore, the following equation is obtained:

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[0054] This gives the following condition on the refractive index of the refrigerant:

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[0055] (EQ1) is

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[0056] is equal to.

[0057] In this embodiment M3, L s While achieving loss-free extraction efficiency of the beam, the L s The beam extraction efficiency can be increased. In this embodiment, a coolant with a higher thermal conductivity than air can be used to remove the heat generated by the LED in the light collector CL while achieving a high loss-free light extraction efficiency. Figure 2D shows the beam L of this embodiment with the same angular coordinates (α, β) as in Figure 2B. g , L s , L out,l and L out,2 In the example diagram of FIG. 3B, the refrigerant is water (n ext = 1.33, θ c,out,1 = 46.6°), and the light collector CL has a refractive index n c The emission medium is a Ce:YAG crystal with n = 1.83. s = 1.22. Surfaces other than the surface to be cooled and the exit surface are in air.

[0058] To achieve better removal of the heat generated in the light collector CL, in one variant of the embodiment shown in Fig. 3A, the second large surface FE2 is also in contact with the coolant CM. Thus, more LEDs and more excitation power can be used, and an output beam with more power can be achieved. Fig. 3B shows the light ray L of this variant, with the same angular coordinates (α, β) as in Fig. 2B. g , L s , L out,1 and L out,2 For example, as shown in FIG. 3B, s =n ext = 1.29, and the light collector CL has a refractive index n c The surface other than the surface to be cooled and the exit surface are in air. The second large surface FE2 is also in contact with the coolant CM, so from FIG. 3B, the light ray L out,1 The critical angle θ of the escape conec,out1 = 33° is the ray L associated with another cooled surface FE2 out,2 The critical angle θ of the escape cone c,out2 = 33°. The refractive index of the refrigerant is equal to the refractive index of the exit medium and the refractive index of the collector,

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[0059] Since the range of angles of the rays exiting the cooled surfaces FE1 and FE2 and the rays L s There is no overlap between the angular range of the output beam L s The light extraction efficiency is lossless.

[0060] L s To increase the extraction efficiency of the beam, one embodiment of the present invention, which is consistent with all previous embodiments of the present invention, comprises a mirror covering the face of the collector opposite to the exit face FL1. Thus, all rays forming the escape cone of face FL3 are reflected in the collector CL and then exit through the exit face, resulting in the exit beam L instead of exiting through FL3. s For example, in the embodiment of FIG. 2B , a mirror covering the face of the collector opposite the exit face FL1 (assuming the mirror has a reflection coefficient of 1 and not considering propagation losses due to absorption in the collector CL) contributes L s The beam extraction efficiency is doubled from 8% to 2 x 8% = 16%.

[0061] In order to achieve the best possible heat removal, in the fourth embodiment M4 of the present invention, all faces of the light collector CL, including the exit face FL1, are in contact with the coolant. s FIG. 4 shows the ray L of this fourth embodiment M4, using the same angular coordinates (α, β) as in FIG. 2B. g , L s , L out,l and L out,2 FIG. 4 shows a plan view of an escape cone of FIG.

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[0062] and the light collector CL has a refractive index n c = 1.83. As can be seen from FIG. 4, these refractive indices are g , L s , L out,1 and L out,2 This means that the critical angle associated with all escape cones of L is equal to sin-1(1.29 / 1.83) = 45°. s n to maximize the lossless extraction efficiency of the beam c n for ext The highest value of n s =n ext This value is calculated from EQ1, assuming that:

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[0063] From various embodiments, in practice, the emission medium n s It is understood that the refractive index of θ is matched to that of the collector and to that of the surrounding medium in contact with other surfaces (i.e., surfaces other than the exit surface and the cooled surface) to limit losses in the light extraction efficiency of the exit beam. Indeed, if the refractive index of the surrounding medium in contact with other surfaces is different from that of the exit medium, then θ c,s +θ c,g >90°, and therefore it is possible to have an overlap between the escape cone of the other surface and the escape cone of the exit surface. Thus, in a preferred embodiment, the exit medium n s The refractive index of θ c,s +θ c,g ≦90°.

[0064] According to a fifth embodiment M5 of the present invention, the refractive index of the coolant CM is such that the loss of light extraction efficiency of the output beam induced by the coolant CM is less than 15%. Figure 5 shows the light ray L of this embodiment M5, using the same angular coordinates (α, β) as in Figure 2B. g, L s , L out,1 and L out,2 3B shows a plan view of the escape cone of FIG. 3B. For example, this device is identical to the embodiment of FIG. 3A. The coolant is water and the exit medium EM has a refractive index n s = 1.5 and has a Ce:YAG crystal. All other surfaces, except the exit and cooled surfaces, are in air. Given the refractive indices and the device configuration, the critical angle associated with the large surfaces (here both cooled surfaces) FE1 and FE2 is θ c,out,1 =θ c,out,2 = sin-1(1.333 / 1.83) = 46.6°. The escape cone associated with surfaces FL2, FL3, and FL4 has a critical angle θ c,g = 33°. The exit medium has a refractive index n s = 1.5, so L s The critical angle of the escape cone of a ray is θ c,s =sin-1(1.5 / 1.83)=55.1°. Therefore, θ c,s +θ c,out,l =θ c,s +θ c,out,2 >90°, and ray L out,l / L out,2 The range of escape cone angles and the ray L s There is an overlap between the angular range of the escape cone of the exit beam L and the exit beam F. This means that rays of luminescence light within this angular range will escape from the collector through the cooled faces FE1 and FE2 instead of passing through the exit face FL1. This results in an exit beam L s With the parameters used to illustrate FIG. 5, the overlap results in a loss of 11.5% in light extraction efficiency in the fifth embodiment M5.

[0065] 6A, 6B, 6C respectively show a perspective view, a side view according to section AB, and a side view according to section CD of a light-emitting device according to another embodiment of the invention. In this embodiment, the cooling system comprises a holder H adapted to support a light collector CL and a number of light-emitting diodes LED. By way of example, the holder can be made of a metal such as aluminum or copper. The holder comprises a flow channel CH adapted to be connected via one end E1 to a water source WS (not shown in FIG. 6A but shown in FIG. 6B). The water flowing in the flow channel CH forms a cooling medium. More precisely, the flow channel is arranged such that the water is in contact with the entire sides FL2 and FL4 and the incident light L d The holder is adapted to transport water flowing from a water source from end E1 to end E2 so as to contact more than 90% of the surface of faces FE1 and FE2 illuminated by the incident light L. The holder comprises a sealing element SE adapted to ensure sealing of the device 1. d The sealing elements in the direct path of are transparent to the incident light. Since the water flowing in the flow channel CH is in contact with most of the surface of the collector CL, the embodiment of FIG. 6A is suitable for removing heat in the collector generated by high values ​​of excitation power (for example, for several thousand light-emitting diodes). For a collector with dimensions 105 mm x 22 mm x 1 mm, a water flow of 4 L / min, and a temperature difference between the water and the collector of 10°C, the light-emitting device of FIGS. 6A-6C can extract a maximum heat power of 185.4 W through the coolant. This calculation was performed using finite element analysis. In comparison, if the cooled surfaces are only the surfaces FE1, FE2, a heat power of 177.3 W can be extracted. This shows that the large surface is much more efficient in cooling the collector. If the coolant in the device of FIGS. 6(A)-6(C) was air, only a heat power of 12.3 W could be extracted.

[0066] FIG. 7 shows a light-emitting device according to another embodiment of the invention. In this embodiment, the cooling system comprises a layer P in a heat-conducting material that conducts heat to a mechanical radiator MR. The layer P forms a coolant CM. In the embodiment shown in FIG. 7, the face FE1 of the light collector excited by the diode LED is the same as the face in contact with the layer P. Therefore, in this embodiment, the layer must be transparent to the incident light emitted by the LED. As an example, the layer is in CaF2 or sapphire. Furthermore, preferably, the mechanical radiator MR is placed outside the path of the incident light so as not to block said incident light. In the embodiment of FIG. 7, the device 1 comprises a thin sublayer G, typically an optical adhesive, that bonds the layer P to the cooled face FE1. This sublayer G is optional.

[0067] The embodiment of FIG. 7 is suitable for removing heat within the light collector generated by moderate values ​​of excitation power (eg, for a few hundred light emitting diodes).

[0068] 8 shows a light emitting device according to another embodiment of the invention, which comprises a cascade of two luminescent collectors CL, CL'. In this embodiment, as an illustrative example, the only cooled surface of the collector CL is the large surface FE1. The output beam L s passes through an exit face FL1 of the collector CL, which is in contact with the exit medium EM, before exciting an additional collector CL′ via a so-called receiving face RF, which is also in contact with the exit medium EM. s and thereafter emitting an additional luminescence radiation. As explained above, a part of the additional luminescence radiation passes through a so-called additional exit surface FL1' of the additional collector and forms an exit beam L's. The additional exit surface FL1' has a refractive index n' s In one example, all surfaces other than the cooled surface FE1, the exit surface FL1, the additional exit surface FL1', and the receiving surface RF are in air. In the embodiment of FIG. 8, the exit medium is s and to maintain mechanical contact between the two light collectors CL and CL'.

[0069] As with all previous embodiments, in the embodiment of FIG. 8, the refractive index of the refrigerant, n ext is the exit beam L guided by the coolant s The refractive index of the output medium and the refractive index of the collector CL are matched to limit the loss in the light extraction efficiency of the additional output beam L´. s To achieve the highest possible extraction performance, the refractive index n of the output medium EM s is the refractive index of the additional collector CL' and the refractive index of the additional exit medium n' s More precisely, the refractive index of the exit medium, n s is such that there is no overlap between the escape cone of the additional luminescent light associated with the surface FL1′ and the escape cone of the additional luminescent light associated with the surface RF. Thus, in one variant of the embodiment of FIG. 8, an efficient cascading of luminescent collectors is achieved to provide an additional output beam L′ s 8, mirrors cover the sides of the additional collector other than the additional exit surface FL1'.

Claims

1. A light emitting device 1, a plurality of light emitting diodes LED configured to emit incident light Ld; Two parallel surfaces along the horizontal plane xy, called the first large surface FE1 and the second large surface FE2, and two parallel surfaces, called side surfaces FL1, FL2, FL3, and FL4, are provided. [0010] Refractive index n ｃ a solid-state light-emitting collector CL, wherein at least one of the first large surface and the second large surface is illuminated by the incident light Ld, the collector absorbs the incident light Ld and then emits luminescent light L Ｌ A portion of the luminescence light is guided by total internal reflection Lg within the light collector, with a refractive index n ｓ <n ｃ The emitted beam L passes through a so-called first exit surface of the light collector FL1 in contact with the exit medium EM. ｓ A solid-state light-emitting collector CL forming a so-called cooling system CS comprising a coolant CM in contact with at least one of the faces of a collector, called cooled face FE1, said cooling system adapted to remove at least a part of the heat generated in said collector by said plurality of light-emitting diodes, said coolant having a refractive index n ｅｘｔ is n ｃ >n ｅｘｔ >1, and n ｓ ≠n ｅｘｔ and a cooling system adapted to the refractive index of the output medium and the refractive index of the collector so as to limit losses in light extraction efficiency of the output beam induced by the coolant; 23. A light emitting device comprising:

2. 10. The device of claim 1, wherein the refractive index of the coolant is such that the loss in light extraction efficiency of the output beam is 15% or less.

3. The refractive index of the refrigerant is [0025] The device according to claim 1 or 2, wherein

4. 3. The device of claim 1 or claim 2, wherein the coolant is in contact with at least 90% of the cooled surface.

5. 3. The device of claim 1 or claim 2, wherein the coolant is in contact with the first major surface and the second major surface.

6. 3. A device according to claim 1 or 2, wherein the cooling system comprises a layer P in a thermally conductive material which conducts heat to a mechanical radiator MR, said layer forming the coolant.

7. 3. The device of claim 1 or claim 2, wherein the coolant is water.

8. 8. The device of claim 7, wherein the cooling system comprises a holder H adapted to support the light collector and the plurality of light emitting diodes, and a flow path CH connected to a water supply WS, the flow path adapted to transport the water, and the holder comprising a sealing element adapted to ensure sealing of the device.

9. 3. The device of claim 1 or 2, further comprising a mirror covering a surface of the light collector opposite the exit surface.

10. An additional solid-state light-emitting collector CL' is provided, and the output beam L ｓ excites the additional collector CL′ via a so-called receiving surface RF of the additional collector in contact with the output medium EM, which further excites the output beam L ｓ and then emits an additional luminescence radiation, part of which passes through a so-called additional exit surface FL1′ of the additional collector and forms an exit beam L′ ｓ and the additional exit surface FL1' has a refractive index n' ｓ and an additional exit medium EM′ having a refractive index n ｓ is the refractive index of the additional light collector CL' and the refractive index n' of the additional exit medium EM' ｓ and said additional exit beam L' ｓ 3. The device according to claim 1 or claim 2, which achieves the highest extraction efficiency of 100%.

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