WO2013136250A1

WO2013136250A1 - An led device comprising a cooling liquid with suspended phosphor particles

Info

Publication number: WO2013136250A1
Application number: PCT/IB2013/051909
Authority: WO
Inventors: George Hubert BOREL; Jorgen Meeusen
Original assignee: Koninklijke Philips N.V.
Priority date: 2012-03-15
Filing date: 2013-03-11
Publication date: 2013-09-19

Abstract

A light emitting unit (1) comprises a lighting vessel (3) for containing a liquid material (29), and a light source comprising at least one light emitting diode (9), at least the light emitting part (11) of the light emitting diode (9) being positioned in the lighting vessel (3) to be in heat conductive connection with the liquid material (29). The lighting vessel (3) comprises a liquid inlet (13) and a liquid outlet (15). In an embodiment the lighting vessel (3) is connected by the liquid outlet (15) and the liquid inlet (13) to a circuit comprising a heat transfer surface (19).

Description

An LED device comprising a cooling liquid with suspended phosphor particles

FIELD OF THE INVENTION

The present invention relates to a light emitting unit comprising a lighting vessel for containing a liquid material, and a light source comprising at least one light emitting diode, at least the light emitting part of the light emitting diode being positioned in the lighting vessel to be in heat conductive connection with the liquid material.

The present invention further relates to a light emitting device comprising the light emitting unit.

BACKGROUND OF THE INVENTION

Light emitting diodes will in the following i.a. be referred to as LEDs.

In lighting applications that incorporates light emitting diodes (LEDs), especially high power LEDs, there is a need for cooling. This cooling is usually provided on the non light emitting side of the LEDs by the use of heat sinks. A lot of applications are using a phosphor attached to the LED, to convert the light of the LEDs this leaves a heat transfer path starting at the phosphor, which is the thermal hotspot, all the way down through the LEDs to the heat sink resulting in a high thermal resistance.

It should be noted that generally a phosphor material or a phosphor, is a substance that exhibits the phenomenon of luminescence.

JP-A-20084689 discloses a light emitting diode package comprising a case member housing an LED and a liquid refrigerant surrounding the LED. Phosphor particles are suspended in the refrigerant, and in use the refrigerant transfers heat from the LED to the walls of the casing member by convection. From the walls of the casing member the heat is transferred on to the surroundings. The casing member is mounted together with the LED on a printed circuit board. Thus this piece of prior art involves the problem that the outside of the walls of the casing member need to be cooled and a problem of cooling is still attached to the area of the printing circuit board where the LED is mounted.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome this problem, and to provide a light emitting unit and a light emitting device allowing use of high power LEDs.

According to a first aspect of the invention, this and other objects are achieved by a light emitting unit as mentioned in the introductory paragraph which is characterized in that the lighting vessel comprises a liquid inlet and a liquid outlet. The liquid inlet and outlet allow for flowing liquid material through the lighting vessel to cool the light emitting diode and subsequently transfer the liquid material to a different place for cooling the liquid material at a place where disposal of the heat does not pose a problem. This further provides freedom of design when the light emitting device of the invention is to be incorporated as a light source in a lighting aggregate i.a. because the light emitting device may be build small relative to its power and does not need to be directly attached to a heat sink.

In an embodiment the light emitting diode is positioned to be in physical contact with the liquid material. This facilitates heat transfer from the light emitting diode to the liquid.

In another embodiment a layer of solid material is isolating the light emitting diode from physical contact with the liquid material, said layer providing for conduction of heat between the light emitting diode and the liquid material. This facilitates sealing a liquid circuit comprising the lighting vessel. The solid material may comprise a thin layer of silicone material.

It is noted that generally heat are transferred in three different ways, namely by

(electromagnetic) radiation, by convection of a fluid, e.g. liquid, material, and by conduction (through a material). The invention utilises the latter to transfer heat from the LED to the liquid material. Once the heat has entered the liquid material the heat is carried away from the LED by convection of the liquid.

According to a second aspect of the invention a light emitting device is provided in that the lighting vessel of a light emitting unit is connected by the liquid outlet and the liquid inlet to a circuit comprising a heat transfer surface. Hereby the heat transfer surface may provide for disposal of the heat.

In an embodiment the heat transfer surface is provided by a heat exchanger. In an embodiment the circuit comprises a pump. Hereby circulation of the liquid material is facilitated independently on the mutual position of the lighting vessel and heat transfer surface.

In an embodiment the circuit comprises an expansion vessel. Hereby thermal expansion of the liquid material may be absorbed. In a further embodiment the expansion vessel is provided by a hydrophore. Hereby a certain pressure may be maintained in the circuit.

In an embodiment the circuit is moisture proof sealed.

Put into practical use the circuit of the light emitting device including the lighting vessel may contain a liquid material, which may be selected from a group

comprising oils, paraffin, and chlorinated paraffin. If the liquid material comprises a liquid component selected from a group comprising paraffin and chlorinated paraffin, a binder may be comprised preventing the paraffin or chlorinated paraffin from separating. By

incorporating the lighting vessel in a liquid circuit with a heat transfer surface for cooling a very effective cooling of the light emitting diode is provided for facilitating an increased luminous flux output using a high power LED.

In an embodiment particles of a phosphor material are suspended in the liquid material. Hereby is obtained that the liquid material with the phosphor material serves as an optical volume diffuser converting and diffusing the light emitted by the light emitting diode. Further effective cooling of the phosphor material, which is a hot spot in a system using phosphor converted light from LED's, is obtained due to the phosphor material circulating with the liquid material past the heat transfer surface to be cooled together with the liquid material.

In an embodiment the particles of phosphor material comprise microscopic particles. Hereby is obtained that the phosphor material particles are not individually visible and emission of uniformly diffused light by the light emitting device is facilitated.

In an embodiment the phosphor material comprises at least one phosphor component selected from a group comprising organic phosphors, inorganic yellow-green phosphors, and reddish inorganic phosphors.

The inorganic yellow-green phosphors may be selected from a group comprising YAG and Luag SSONE, and the reddish inorganic phosphors may be selected form a group comprising ECAS101, ECAS102, and BSSNe.

It is noted that the invention relates to all possible combinations of features recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other aspects of the present invention will now be described in more detail, with reference to the appended schematic drawings showing embodiment(s) of the invention. In the drawings Fig. 1 shows a diagram of a light emitting device according to the invention; Fig. 2 shows a section of an embodiment of a light emitting unit; and

Fig. 3 shows a section of a different embodiment of a light emitting unit.

DETAILED DESCRIPTION

Fig. 1 shows a light emitting device comprising a light emitting unit 1 with a lighting vessel 3 having a bottom 5 and a transparent or translucent top wall 7. At the bottom 5 a plurality of light emitting diodes (LEDs) 9 are provided, the LEDs 9 having respective light emitting parts 11 facing the top wall 7. The lighting vessel 3 has a liquid inlet 13 and a liquid outlet 15. The light emitting device further comprises a heat exchanger 17 with a heat transfer surface 19 and a fan 21; a pump 23; and a reservoir tank embodied as a hydrophore 25.

Conduits 27 connect the above elements of the light emitting device to provide a circuit. Thus a first conduit 27a connects the liquid outlet 15 of the lighting vessel 3 and the heat exchanger 17, a second conduit 27b connects the heat exchanger 17 and the hydrophore 25, a third conduit 27c connects the hydrophore 25 and the pump 23, and finally a forth conduit 27d connects the pump 23 and the liquid inlet 13 of the lighting vessel 3.

The circuit thus provided by the lighting vessel 3, the heat exchanger 17, the hydrophore 25 and the pump 23 is filled with a liquid material 29, such an oil material, having particles of a phosphor material suspended therein as indicated by dots 31 in the lighting vessel 3.

In the embodiment illustrated in Fig. 2 the light emitting parts 11 of the LEDs 9 are in physical contact with the liquid material 29 in the lighting vessel 3. Thereby the light emitting parts 11 of the LEDs 9 are in heat conductive connection with the liquid material 29, which thus provides for cooling the LEDs 9.

In the embodiment illustrated in Fig. 3 a thin layer 33 of solid material or sheet, such as a silicone material, is isolating the LED's 9 from physical contact with the liquid material 29. In this embodiment the light emitting parts 11 of the LEDs 9 are in heat conductive connection with the liquid material 29, the layer 33 of solid material conducting heat from the LED's 9 to the liquid material 29, which thereby provides for cooling the LED's 9. The layer 33 of e.g. silicone material facilitates the provision of a sealed, especially moisture proof sealed lighting vessel 3 (apart from the liquid inlet and liquid outlet), which is beneficial if the phosphor material used is degradable by moisture.

The LEDs 9 may e.g. be of InGaN-type providing light of Royal Blue color. The liquid material 29 may be chosen from a group comprising oils, paraffin, and chlorinated paraffin. When paraffin or chlorinated paraffin is used a binder may be added to prevent the paraffin or chlorinated paraffin from separating. Such measure is per se known in the art. The liquid material should be liquid at the surrounding temperature where the light emitting device is intended to be used.

A number of different phosphors are known in the art and the phosphor material may e.g. be chosen from group comprising organic phosphors, inorganic yellow- green phosphors, i.e. phosphors emitting light in the yellow-green range, such as e.g. YAG and Luag SSONE, and reddish inorganic phosphors, i.e. phosphors emitting reddish light, such as e.g. ECAS101, ECAS102, and BSSNe. The actual phosphor to be chosen may depend on the actual type of LEDs used to provide for the light emitting unit to emit light of an intended color.

The size distribution of the particles of phosphor material may vary from microscopic particles that will give the respective liquid material a uniform diffuse glove when illuminated by the LED's, to macroscopic particles that will be individually visible. Microscopic particles may have sizes ranging from nano-scale to e.g. 100 μιη. Macroscopic individually visible particles may provide for inspection of whether the liquid material is flowing through the lighting vessel 3.

The liquid material 29 and the phosphor material 31 may be chosen to have similar densities to provide for the particles of phosphor material 31 to float in the liquid material 29. However the circulating movement of the liquid material 29 will provide for stirring up the particles of phosphor material 31 facilitating their suspension in the liquid material 29.

The hydrophore 25 provides for maintaining an overpressure in the circuit which e.g. is beneficial when the embodiment shown in Fig. 3 of the lighting unit 1 is used, since the overpressure will ensure contact between the sheet or layer 33 and the light emitting parts 11 of the LEDs 9 thereby providing for good transfer of heat from the LEDs 9 to the layer 33 from where the heat is further transferred to the liquid material 29.

In use the LEDs 9 emit light towards the top wall 7 through the liquid material 29 and the particles of phosphor material 31 convert the light or at least a part thereof, before it is transmitted through the top wall 7. Thereby the liquid material 29 with the particles of phosphor material 31 suspended therein acts as a volume diffuser providing for light mixing. The pump 23 circulates the liquid material 29 from the lighting vessel 3 to the heat exchanger 17 for the liquid material 29 to pass the heat transfer surface 19 which is cooled by surrounding air driven by the fan 21. The liquid material 29 thus cooled is then circulated from the heat exchanger 17 through the hydrophore 25 and the pump 23 back to the lighting vessel 3.

The invention provides freedom of design for a designer who is constructing a lighting implement incorporating a light emitting device since the light emitting unit may be quite small not needing to be attached to a solid heat sink and accordingly and may be placed in a confined space with reduced circulation of surrounding air to cool the light emitting unit while the other components of the light emitting device may be placed remote from the light emitting unit where space is available.

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, a pressure less expansion vessel may be used as the reservoir tank instead of the hydrophore shown. Further the reservoir tank whether embodied as a hydrophore or not, may be attached to a blind end branch instead of having the liquid material flowing continuously through. Other types of LEDs, other types of liquid material and other types of phosphor material than the types specifically mentioned may be used.

Claims

CLAIMS:

1. A light emitting unit (1) comprising a lighting vessel (3) for containing a liquid material (29), and a light source comprising at least one light emitting diode (9), at least the light emitting part (11) of the light emitting diode (9) being positioned in the lighting vessel (3) to be in heat conductive connection with the liquid material (29), character- i z e d in that the lighting vessel (3) comprises a liquid inlet (13) and a liquid outlet (15).

2. A light emitting unit (1) according to claim 1, characterized in that the light emitting diode (9) is positioned to be in physical contact with the liquid material (29).

3. A light emitting unit (1) according to claim 1, characterized by a layer (33) of solid material isolating the light emitting diode (9) from physical contact with the liquid material (29), said layer (33) providing for conduction of heat between the light emitting diode (9) and the liquid material (29).

4. A light emitting unit (1) according to claim 3, characterized in that the solid material comprises a silicone material.

5. A light emitting device comprising a light emitting unit (1) according to any of claims 1 to 4, characterized in that the lighting vessel (3) is connected by the liquid outlet (15) and the liquid inlet (13) to a circuit comprising a heat transfer surface (19).

6. A light emitting device according to claim 5, characterized in that the heat transfer surface (19) is provided by a heat exchanger (17).

7. A light emitting device according to claim 5 or 6, characterized in that the circuit comprises a pump (23).

8. A light emitting device according to any of the claims 5 to 7, characterize d in that the circuit comprises an expansion vessel (25).

9. A light emitting device according to claim 8, characterized in that the expansion vessel is provided by a hydrophore (25).

10. A light emitting device according to any of the claims 5 to 9, characterize d in that the circuit is moisture proof sealed.

11. A light emitting device according to any of the claims 5 to 10, characterize d in that the circuit including the lighting vessel (3) contains a liquid material (29).

12. A light emitting device according to claim 11, characterized in that the liquid material (29) is selected from a group comprising oils, paraffin, and chlorinated paraffin.

13. A light emitting device according to claim 11 or 12, characterized in that particles of a phosphor material (31) are suspended in the liquid material (29).

14. A light emitting device according to claim 13, characterized in that the particles of phosphor material (31) comprise microscopic particles.

15. A light emitting device according to claim 13 or 14, characterized in that the phosphor material (31) comprises at least one phosphor component selected from a group comprising organic phosphors, inorganic yellow-green phosphors, and reddish inorganic phosphors.