GB2335265A

GB2335265A - Cooling means for a planar lamp

Info

Publication number: GB2335265A
Application number: GB9903359A
Authority: GB
Inventors: Murat Oklay
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1998-03-10
Filing date: 1999-02-16
Publication date: 1999-09-15
Anticipated expiration: 2019-02-16
Also published as: GB9903359D0; GB2335265B

Abstract

Cooling means 2 for a lamp 1 comprising a recess to receive a planar lamp 1, a plenum chamber 28 extending generally parallel and spaced from the rear face of the lamp 11 with a plurality of gas outlet orifices 25 situated on its forward wall arranged such that cooling gas emerges through said orifices as jets impinging on the rear face 11 of the lamp. The impinging jets are at an angle to promote efficient heat transfer and may be normal to the rear face of the lamp. The rear face of the lamp may be roughened to break up the boundary layer of air over the its surface. An electrical heating 12 element is supplied warm the lamp initially. Cooling gas is supplied to the plenum chamber via an inlet 23 connected via an air hose to a fan, impeller etc.

Description

1 LAMP ARRANGEMENTS 2335265 This invention relates to lamp arrangements

and to methods of cooling lamp arrangements.

Fluorescent lamps are often used to backlight displays, such as in aircraft instruments. To ensure optimum illumination, the lamps need to operate within a restricted temperature range. It is often necessary, therefore, to heat the lamp prior to start up, and to cool the lamp during operation. The usual way in which the lamp is heated is by means of an electrical heating element in close thermal contact with the lamp; with flat panel lamps this heating element is conveniently attached to the rear face of the lamp. The usual way in which the lamp is cooled is by means of a heat sink having a large thermal mass in close thermal contact with the lamp; this usually takes the form of a block of metal, which may be profiled with fins or the like to promote cooling. Although such an arrangement may function satisfactorily in many applications, it causes problems where the lamp has to be rapidly warmed from a very low temperature. This is because the heat sink thermally attached with the lamp for cooling purposes will dissipate a significant part of the heat supplied by the heating element, thereby increasing the time taken to achieve the optimal temperature.

It is an object of the present invention to provide an improved lamp arrangement and method of cooling.

According to one aspect of the present invention there is provided a lamp arrangement comprising a lamp and cooling means, the lamp having a generally planar rear face and the 0 2 cooling means including a plurality of gas outlet orifices distributed over the rear face of the lamp and arranged such that cooling gas emerges through said orifices as jets impinging on 0 the rear face of the lamp at an angle to promote efficient transfer of heat from the lamp to the cooling gas.

The cooling means preferably has a generally planar plenum chamber with a forward wall extendina cenerally parallel to and spaced from the rear face of the lamp, the outlet orifices being formed in said forward wall. The orifices are preferably elongate slots extending parallel with one another. The spacing of the rear face of the lamp from the orifices is preferably between about four to five time the width of each orifices. The orifices may be about 1 mm wide. The impinging jets are preferably incident on the rear face of the lamp substantially normal to the face of the lamp. The rear face of the lamp may be roughened and preferably supports an electrical heating element. The cooling unit may include a casing with a recess in which the lamp is received.

Accordine, to another aspect of the present invention there is provided a cooling unit 0 for a lamp including a casing having a recess shaped to receive the lamp, a plenum chamber including a ftont wall having a plurality of gas outlet orifices opening into the recess, and a spacer for spacing a rear wall of the lamp from the front wall of the plenum chamber, and an inlet for cooling gas, the orifices being arranged such that cooling gas emerges through the orifices as jets impinging on the rear face of the lamp at an angle to promote efficient transfer of heat from the lamp to the cooling gas.

3 According to a ftirther aspect of the present invention there is provided a method of cooling a lamp of generally planar form comprising the step of impinging jets of a cooling gas onto a rear face of the lamp at a plurality of locations distributed over the rear face of the lamp. The jets are preferably produced by elongate slots.

A lamp arrangement and a method of cooling a lamp, according to the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 Figure 2 Figure 3 is a schematic perspective view of the lamp arrangement; is a perspective view of the ftont of the cooling means of the lamp arrangement in more detail; and is a perspective view of the front of the cooling means of Figure 2, with its front panel removed.

With reference first to Figure 1, the lamp arrangement comprises a planar lamp 1 and cooling means 2 in the form of a unit located behind the lamp. The lamp 1 may be of any conventional form requiring cooling and, in the present example, is a flat panel fluorescent lamp, such as of the kind used to backlight displays. The lamp 1 is rectangular with a front face 10, from which light is emitted, and a rear face 11, which may be opaque. A serpentine electrical heating element 12 is attached to the rear face 11 of the lamp, the element being connected to a heating control unit 13.

4 With reference now also to Figures 2 and '), the cooling means 2 includes a casing 20 of generally rectangular shape and having a section 21 to receive the lamp electrodes (not shown). The casing 20 is preferably moulded of a lightweight, thermally-insulating plastics material. The rear wall 22 of the casing has an opening 23) for the inlet of air or other cooling gas, the inlet being in the form of a slot extending across the width of the casing 20. The front wall 24 of the casing is provided by a removable panel having fourteen jet outlets 2 5 in the form of narrow, parallel slots extending across the width of the casing 20 and distributed along its entire length. The front panel 24 is set back from the front of the casing by about half the depth of the casing leaving a recess 26 in which the lamp 1 is received. The front panel 22 carries spacers 27, which space the front face of the panel 24 from the rear face 11 of the lamp 1 by a distance z,, equal to between four and five times the width B of the jet outlet slots 25. Typically, the width B of the slots 25 is about I mm and the spacing z,, between the lamp 1 and the slots is about 5mm. The rear surface of the front panel 24 is spaced from the rear wall 22 of the casing 20 by a gap so that a plenum chamber 28 is formed within the casing The inlet 23 is connected via an air hose 29 to a fan, impeller or some other source of cooling gas 3 0, which may be used to supply cooling air to other equipment.

Air from the fan '10 flows into the plenum chamber 28 through the inlet 23 and flows out of the chamber through the slots 25. Because the slots 25 are narrow, the air emerges from each slot as a jet, the width of which extends along the length of the slots. The spacing of the rear face 11 of the lamp 1 from the slots 25 is sufficiently small to ensure that the jets impinge on the lamp face and effect a highly efficient transfer of heat from the lamp face to the impinging air. This transfer of heat is optimum when the lamp 1 is spaced from the slots 25 by a distance between 4-5 times the width of the slots. The heating element on the rear face 11 of the lamp 1 provides a roughened surface, which helps break up the boundary layer of air over the rear surface. The rear face 11 could be roughened in other ways. After impinging on the rear face 11 of the lamp 1, the air flows away through a gap between the rear face of the lamp and the bottom edge ') 1 of the casing 20.

Instead of using narrow slots to produce the impinging jets, they could be produced by holes of different shapes, although the arrangement of slots has been found to be the most efficient.

The arrangement of the present invention enables lamps to be cooled efficiently without the need for any heat sink. Thus, when it is necessary to warm the lamp 1, the control unit 13 energizes the heating element 12 and the fan ^30 is held off, or its outlet diverted to other equipment. The major part of the heat produced by the element 12 is, therefore, conducted into the structure of the lamp 1. This enables the lamp 1 to be warmed rapidly and keeps power consumption to a minimum. The thermally-insulating nature of the casing 20 helps promote this heating. The casing 20 can also provide a lightweight structural support for the lamp.

6

Claims

A lamp arrangement comprising a lamp and cooling means, wherein the lamp has a generally planar rear face, and wherein the cooling means includes a plurality of gas outlet orifices distributed over the rear face of the lamp and arranged such that cooling gas emerges through said orifices as jets impinging on the rear face of the lamp at an angle to promote efficient transfer of heat from the lamp to the cooling gas.
2. An arrangement according to Claim 1, wherein the cooling means has a plenum chamber with a forward wall extending generally parallel to and spaced from the rear 0 face of the lamp, and wherein the outlet orifices are formed in the forward wall.
3. An arrangement according to Claim 1 or 2, wherein the orifices are elongate slots extending parallel to one another.

C
4. An arrangement according to any one of the preceding claims, wherein the spacing of the rear face of the lamp from the orifices is between about four to five times the width of each orifice.
An arrangement according to any one of the preceding claims, wherein the orifices are about I mm wide.
6. An arrangement according to any one of the preceding claims, wherein the impinging tP jets are incident on the rear face of the lamp substantially normal to the face of the lamp.
7. An arrangement according to any one of the preceding claims, wherein the rear face of the lamp is roughened.
8. An arrangement according to any one of the preceding claims, wherein the rear face of the lamp supports an electrical heating element.
9. An arrangement according to any one of the preceding claims, wherein the cooling means includes a casing with a recess in which the lamp is received.
10. A lamp arrangement substantially as hereinbefore described with reference to the accompanying drawings.
A cooling unit for a lamp including a casing having a recess shaped to receive the lamp, a plenum chamber including a front wall having a plurality of gas outlet orifices opening into the recess, and a spacer for spacing a rear wall of the lamp from the front wall of the plenum chamber, and an inlet for cooling gas, wherein the orifices are arranged such that cooling gas emerges through the orifices as jets impinging on the rear face of the lamp at an angle to promote efficient transfer of heat from the lamp to the cooling gas.
12.

A method of cooling a lamp of generally planar form comprising the step of impinging jets of a cooling gas onto a rear face of the lamp at a plurality of locations distributed over the rear face of the lamp.
13. A method according to Claim 12, wherein the jets are produced by elongate slots.
14. A method of cooling a lamp substantially as hereinbefore described with reference to the accompanying drawings.

Any novel and inventive feature or combination of features as hereinbefore described.