A light fitting in accordance with the first paragraph is already known through EP 0 446 692. In this case the light from the light source is led in a light guide made of glass or plastic material. Even though the light-guide material has an obviously lower heat conductivity than normal metals, the heat conducted into, for example, a cold-storage room is unacceptably large.

This invention is mainly intended to be used for such applications where it is required to separate off the radiating unit, consisting of the power unit, light source and reflector, by means of a wall or the like and preferably in such situations where it is required to locate the radiating unit on the outside of a cooler area such as a cold-storage room. By locating the radiating unit on the outside of a cold-storage room the energy costs can be reduced, as only light enters the cold-storage room and the excess heat is discharged outside the cold area. Preferably a light source is used with a low IR radiation.

When locating the radiating unit on the outside of a cooler area, it is of great importance to prevent the leakage of heat through the wall inlet. The thermal insulation of the wall must not be impaired and problems with condensation and/or the formation of ice must be avoided. The purpose of this invention is to achieve a simple and reliable solution to the problem of the leakage of heat in combination with a light fitting that is easy to install.

The aim of the invention is achieved by means of a light fitting characterized by the end of the light pipe facing the reflector being provided with a surrounding insulating pipe, by the light pipe, the transparent plate and a sealing end plate situated at the end of the light pipe facing away from the reflector being designed to form the boundaries of a closed airspace, which airspace boundaries in conjunction with the airspace distribute the light along the light pipe before transmission through the airspace boundaries so formed and by the transparent plate being designed to form, when in position, an airtight connection with the light pipe and to form a seal with the surrounding insulating pipe, whereby the air trapped in the light pipe between the plates acts as thermal insulation and thereby prevents the leakage of heat via the light pipe, and also a procedure characterized by: - the surrounding insulating pipe being installed in the wall, - the section of light pipe with the transparent plate fitted on the end being inserted from the screened-off area and aligned in the correct position, - the transparent plate being sealed with the surrounding insulating pipe, - the power unit, light source and reflector being installed on the outside of the wall and the reflector being connected to the end of the light pipe fitted with the plate.

By means of this invention a completely sealed light pipe is achieved. The sealed pipe with its stationary air effectively prevents the leakage of heat from the reflector end through the pipe. The air in the light pipe acts as a thermal barrier to conventional heat conduction.

In accordance with an advantageous embodiment of the light fitting, it is characterized by the periphery of the transparent plate being provided with a ring with recesses and by a seal being placed between the ring on the transparent plate and the surrounding insulating pipe. This construction provides a completely airtight connection between the transparent plate and the surrounding insulating pipe.

A further advantageous embodiment of the light fitting has flexible insulation inserted in the space between the light pipe and the surrounding insulating pipe at the part of the surrounding insulating pipe facing away from the reflector. By means of the flexible insulation that does not need to be completely airtight, an air-filled space is closed off around the light pipe between the light pipe and the surrounding insulating pipe. The air-filled space provides good thermal insulation between the surrounding insulating pipe and the light pipe.

The light pipe is made preferably out of a material with low thermal conductivity and small light losses, for example polycarbonate or acrylic plastic. This choice of material results in the light pipe acting as a poor conductor of heat at the same time as efficiently transmitting the light out into the cold-storage room.

An advantageous procedure for installing a light fitting is characterized by the transparent plate being sealed with the surrounding insulating pipe by the use of a seal in contact with the surrounding insulating pipe and a ring around the periphery of the transparent plate and by the appiication of an adhesive, for example a silicon adhesive, in contact with the surrounding insulating pipe and the ring on the transparent plate. This prevents leakage of warm air into the cold-storage room, which would result in condensation in the cold-storage room.

The surrounding insulating pipe is advantageously sealed with the wall using an adhesive, for example silicon adhesive.

In a further advantageous procedure according to the invention, flexible insulation is inserted between the surrounding insulating pipe and the light pipe at the end of the surrounding insulating pipe facing away from the reflector.

In the case where the light pipe is constructed of a number of sections, the sections can be advantageously installed one after the other working away from the power unit and the joints between the sections sealed by means of a suitable method, for example with tape.

The invention will be described in greater detail below with reference to the enclosed drawings, where figure 1 shows diagrammatically and partly in section a light fitting according to the invention installed with a wall inlet and figure la shows partly in section in greater detail the part of the light fitting in figure 1 marked la.

The light fitting shown in figure 1 consists of a power unit 1, a light source 2 and a focusing reflector 3 mounted on one side of an insulated dividing wall 4.

An insulating pipe 5 is fitted in the dividing wall 4 and sealed with the dividing wall by means of a sealing adhesive. The insulating pipe 5 contains one end of a light pipe 6. The end of the light pipe situated inside the insulating pipe is terminated with a silicon ring 7 surrounding a glass plate 8 that forms a window for the light. The silicon ring is joined by an airtight connection, for example by gluing, to the light pipe 6 and the glass plate 8. The silicon ring 7 is also joined by a completely airtight connection to the insulating pipe 5 by means of a thin seal 9 in combination with sealing adhesive 10, for example silicon adhesive. At the inner part of the wall a special insulation 11 is inserted between the light pipe 6 and the insulating pipe 5. An air-filled space 1 2 around the light pipe is bounded by the outer surface of the light pipe and the inner surface of the insulating pipe in combination with the insulation 11 and the seal at the silicon ring 7. The insulation does not need to be completely airtight, but must prevent the free ventilation of the space 1 2. The air-filled space acts as a good thermal insulator between the insulating pipe 5 and the light pipe 6.

The light pipe 6 terminates at the end facing away from the dividing wall 4 in a close-sealing end plate 14. Together with the end plate 8 and the light pipe 6 the end plate 1 4 forms a closed space that makes an effective barrier to the conduction of heat.

Figure 1 a shows in greater detail how the silicon ring 7 can be designed to hold the light pipe 6 and the glass plate 8. According to this design the silicon ring 7 has a first recess 7.1 to hold the light pipe 6 and a second recess 7.2 to hold the glass plate 8. In order to facilitate the fixing of the silicon ring on the light pipe and to create a good seal, the inner edge 7.3 of the recess 7.1 can, as shown, extend beyond the outer edge of the recess.

In short, the light fitting can be said to work as follows: the power unit 1 powers a light source 2 that emits light. The reflector 3 focuses the light from the light source and directs it into the light pipe 6 through the glass plate 8. By means of its design the light pipe 6 distributes the light in the required way along all its length with small losses. Examples of films that can be used for light pipes are described in the article "PRISMATIC FILM LIGHT GUIDES; PERFORMANCE AND RECENT DEVELOPMENTS" by Steven G. Saxe, Solar Energy Materials 19 (1989) 95 109 North-Holland, Amsterdam, pages 95 - 109.

The light is distributed along the light pipe by means of preferably repeated diffractions and reflections varying for different components of the light before it finally reaches such an angle of incidence that transmission can take place and the light is then allowed to leave the pipe.

The installation of the light fitting must be carried out in a certain way in order to avoid condensation, etc. A suitable installation procedure is described below, step by step.

1. The insulating pipe 5 is installed in the wall 4 and sealed with the wall.

2. The light pipe is normally made up of a number of sections of suitable length so that the installation of a complete light pipe can be carried out on site. The section that is to be inserted in the wall 4 is taken into the cold-storage room first. Prior to insertion the end of the section that is to be inserted into the insulating pipe 5 is fitted with a silicon ring 7 surrounding a glass plate 8. It is ensured in a suitable way that the section is emptied of warm air and that this is replaced with cold air from the cold-storage room. Thereafter the end of the light pipe with the silicon ring is inserted through the insulating pipe 5 and the pipe is aligned using the supports not shown in the figure.

3. The thin seal 9 is inserted between the silicon ring 7 and the insulating pipe 5 and sealed carefully with silicon adhesive.

4. The reflector 3 is fitted on the power unit 1 and fixed in its supports. The reflector is usually fitted right up to the silicon ring 7 in order to avoid the loss of light. The light source can be switched on in order to check the direction of the light through the pipe but must be switched off while the rest of the installation of the pipe is carried out.

5. After the space 1 2 between the insulating pipe 5 and the light pipe 6 has been filled with cold air from the cold-storage room, the flexible insulation 11 can be inserted between the insulating pipe and the light pipe.

6. The sections are then taken into the cold-storage room one at a time and installed as soon as they have been filled with cold air. Before installation, the far end of the last section is fitted with a silicon ring with a mirror.

7. After all the sections have been assembled, all the joints between the sections are taped so that the light pipe has airtight connections.

8. The light can now be switched on.

It can be pointed out that certain of the stages in accordance with points 1 - 8 above can be carried out in a somewhat modified form or can be combined. For example, the seal in accordance with point 1 can be combined with the seal in accordance with point 3.

By means of the installation procedure described above there is no warm air in the light pipe that can condense and form a coating of ice on the inside of the pipe. Very good thermal insulation is achieved between the wall and the light pipe which prevents the leakage of heat at this point. The air in the light pipe also provides good insulation. The temperature of this air falls quickly from the inside of the glass plate inside the light pipe and immediately inside the wall is down to the temperature of the cold-storage room. The seals on the outside consisting of silicon adhesive and seals prevent warm air from entering and causing condensation. This has been confirmed in practical experiments.

This invention is in no way limited to the embodiment described above, but within the invention as it is defined in the attached patent claims there is also room for many other possible embodiments.