COLD STORE LIGHTING SYSTEM

TECHNICAL FIELD

The invention relates to a light filtering and transmission apparatus. The 5 apparatus finds particular, though not exclusive, utility in a lighting system lighting the interior of a cold store. The invention also relates to a lighting system including light filtering and transmission apparatus, the lighting system finding particular utility in providing light to the interior of a cold storage unit. The invention also relates to use of the lighting system to light the interior of a cold store.

0

BACKGROUND OF THE INVENTION

Large cold storage units are cooled below the environmental ambient temperature to near or below freezing by refrigeration units and are maintained in this cooled state by thick thermal insulation surrounding the unit. These cold stores 5 may be used to chill foodstuffs for warehousing purposes or keep frozen foods, or may provide a cooled area for food preparation.

The lighting systems that are required to light the interiors of these large cold storage units are themselves large, extensive and consume a large amount of power. A significant amount of heat is generated by the lighting systems, particularly by the0 light sources thereof, and as the lighting systems are usually built into the walls (i.e. walls and/or ceilings) of the cold storage units, at least some or all of this heat is typically transmitted into the cold store itself, raising the temperature thereof. The input of this heat from the lighting system must be removed from the cold store by the refrigeration unit, which may significantly increase the power consumption and5 running costs thereof and may also lead to a general or localised elevation in the temperature of the cold store, which may spoil foodstuffs and breach requirements.

To reduce the amount of heat input to a cold store by a lighting system it is known in the art to replace the light sources in the lighting system with more suitable ones which may themselves be expensive and may not lead to a significant0 reduction in the input heat, or to employ complicated and expensive fibre optics to provide light to the cold store. Further, these solutions may lead to a reduced amount of light entering the cold store. SUMMARY OF THE INVENTION

The inventors have recognised that there is a need for an alternative solution the above problem. It is therefore an object of the invention to provide an apparatus for use in a lighting system of a cold store that has the effect of limiting the amount of input heat.

Viewed from one aspect, the invention provides light filtering and transmission apparatus for use in a lighting system lighting the interior of a cold store, comprising: a hollow body defining an evacuated cavity, the body having first and second windows and the light filtering and transmission apparatus being configured such that light can pass through the body between the first and second windows; and heat filtering means arranged to filter light that passes through the hollow body between the first and second windows, the heat filtering means being configured so as to allow transmission of visible wavelengths and suppress transmission of infra-red wavelengths of light through the body.

In accordance with this aspect of the invention, the light filtering and transmission apparatus can be used in a lighting system of a cold store, and when positioned such that light from the light source used to light the interior of the cold store passes between the first and second windows, the apparatus acts to transmit visible light into the interior of the cold store, but not transmit the heat. In particular, the heat filter removes (e.g. by absorption and/or reflection) the thermal infra-red wavelengths from the light spectrum output by the light source, which is otherwise a significant source of heating, thereby suppressing transmission of the thermal infra-red into the cold store. The heat filter allows the visible wavelengths of the spectrum to be transmitted to light the cold store. By suppression, it is meant that the energy of the light transmitted through the apparatus into the cold store at thermal infra-red wavelengths is significantly reduced, preferably with the thermal infra-red being completely or almost completely removed or eliminated.

Further, the provision of the body as a hollow body having an evacuated cavity suppresses heat transfer from the light source into the interior of the cold store by conduction or convection. The portion of the body nearest the light source and first illuminated thereby may be heated by the light source, either by absorption of thermal radiation (i.e. infra-red light) produced thereby, or by conduction and convection. However, the evacuated cavity of the hollow body removes the mechanism for heat transfer into the cold store by convection that would otherwise occur in a non-evacuated cavity, and the cavity also provides thermal insulation to relatively reduce heat transfer into the cold store by conduction.

Therefore the light filtering and transmission apparatus enables lighting of the interior of a cold store but limits heat transfer into the cold store by suppressing thermal radiation, conduction and convection.

Further still, the light filtering and transmission apparatus of the invention allows transmission of light produced by a light source located outside a cold store (which may be an artificial or natural light source - e.g. daylight) into the interior of a cold store. This further reduces heat transfer from the light source to the cold store and facilitates maintenance by ease of replacement of the light source (the time during which a maintenance engineer is permitted to be present inside a cold store is typically limited, for safety reasons).

The hollow body may be a tubular member having said first and second windows at its ends. The tube may have a substantially circular cross-section. The tube may be a straight tube having first and second windows at its opposite ends. The tube preferably has an axial length of at least 200mm, more preferably at least 250mm. Further, the tube preferably has an axial length of between 300mm and 600mm, more preferably between 400mm and 550mm, and more preferably still between 450mm and 500mm. These preferred arrangements are particularly advantageous in that tubular constructions are easily manufactured and provide end windows for light entry and exit. Tubes having circular cross sections are particularly advantageous and easy to produce, though tubes having other, non- circular cross sections, are possible. A straight tube provides line-of-sight illumination. Tubular arrangements, particularly those having the aforementioned axial lengths, are particularly suitable for installation in the wall (i.e. wall and/or ceiling) of a cold storage unit extending through the thermal insulation thereof, which is typically between 250mm and 300mm thick. The light source may then be provided outside (i.e. external to), or at least near the outer surface of the thermal insulation surrounding the cold store, which further reduces heat transfer into the cold store, particularly by limiting heat conduction. Further, such tubular and straight-tubular forms are particularly advantageous for easy installation.

The apparatus may be configured such that light is guided between the first and second windows by reflection. The apparatus may further comprise a reflective material arranged to guide light between the first and second windows. The reflective material may be a reflective film or coating arranged on the internal surface of the cavity. Alternatively, the reflective material may be a reflective film arranged on the external surface of the hollow body. These preferred arrangements provide particularly efficient transfer of light into the interior of the cold store to provide light therein, significantly reducing light losses and thereby keeping down the number of required light sources and improving the light levels therein.

The hollow body may have a non-return valve usable to create the vacuum. The hollow body is sealed to maintain the evacuated state therein. To create the evacuated state initially, the hollow body may be formed and sealed (for example by applied windows in a tubular construction) in, for example, an evacuated chamber. Alternatively, the body may have a branch tube through which the cavity is pumped down to a vacuum or near vacuum, and the branch tube may be thereafter sealed shut by, for example, pinching the walls of the branch tube together (for example, if the body and branch tube are made of glass). Alternatively the body may provided with a non-return valve and be formed and sealed in, for example, atmospheric pressure conditions, and the non-return valve be used to out-gas or pump down the cavity to evacuate it.

The heat filtering means may be further configured to suppress transmission of ultraviolet wavelengths of light through the body. Suppression of ultraviolet wavelengths further reduces heat transmission into the interior of the cold store, and also, where a metal halide light source is used, to prevent exposure to potentially dangerous levels of ultraviolet light. Alternatively, and ultraviolet filter may be provided separate to the heat (IR) filter.

The apparatus may further comprise a lens or a diffuser arranged to direct or diffuse light passing through a window of the body. Preferably, a light shaping diffuser is provided to direct and diffuse the light. The lens or diffuser may be provided as or arranged adjacent a said window of the body. The use of lenses or diffusers, separately, in combination, or together as a single unit enables the light transmitted into the interior of the cold store to be directed or diffused as desired. The light filtering and transmission apparatus may be arranged such that the lens and/or diffuser is provided as or arranged adjacent the said window of the hollow body on which light from an associated light source is, in normal use, last incident.

The heat filtering means may be provided as or arranged adjacent a said window of the body. The light filtering and transmission apparatus may be arranged such that the heat filtering means is provided as or arranged adjacent the said window of the hollow body on which light from an associated light source is, in normal use, first incident. Providing the heat filter at or as the light input window is advantageous in the suppression of heat transfer into the interior of a cold store. When the hollow body is provided as a tubular member, the heat filter and the lens(es) and/or diffuser(s) are preferably provided as or at opposite end windows.

Optionally, cooling means may be arranged to cool the heat filter in use. The heat filtering means may become very hot in use, particularly where it is arranged between a window of the hollow body and a high power light source, such as a metal halide lamp. To cool the heat filter, the cooling means may be provided as a fan.

The body of the light filtering and transmission apparatus may comprise an acrylic or polycarbonate material. These preferred materials are particularly advantageous in that they are able to withstand the heat produced by a light source at one portion of the body (where temperatures of up to around 90 degrees Centigrade may be sustained), and the cold of the cold store at another section of the body (where temperatures of minus 30 degrees Centigrade or lower may be sustained), without being prone to frosting or vitrification.

Preferably, the body comprises glass and is surrounded by a protective material. This arrangement is advantageous in that it is cheap and easy to produce, and has low outgassing characteristics. Outgassing treatment may be applied to the hollow body and windows, such as by heating, in order to maintain the vacuum after sealing. Glass is advantageous because is not prone to devitrification on such outgassing treatment. The protective sleeve may, for example, be a suitable thermoplastic resin such as acrylonitrile butadiene styrene (ABS), or polycarbonate, and is provided to protect the glass vacuum tube and reduce the risk of the glass smashing. This is intended to reduce the likelihood of broken glass entering controlled environments inside cold stores, which is undesirable and can be extremely dangerous, particularly in food preparation areas. A transparent protective cover may be arranged to protect the window of the hollow body on which light from an associated light source is, in normal use, last incident. This is also intended to prevent unwanted material, such as broken glass, from entering a controlled clean environment inside a cold store.

One or both of the windows of the light filtering and transmission apparatus may be sealingly adhered to the hollow body by an adhesive which has a low outgassing performance so as not to degrade the evacuation of the hollow body and which is tolerant of thermal cycling an having an operating temperature of -30 °C to 60 ⁰ C, more preferably -30 ⁰ C to 100 ⁰ C, more preferably still -5O ⁰ C to 200 ⁰ C. An example of such an adhesive is Master Bond Polymer Adhesive EP21 -TDCHT-LO, obtainable from Master Bond Inc. of Hackensack, NJ, USA. A low outgassing performance material may be, for example, one for which a sample of the material experiences a total mass loss, determined from its weight before and after exposure to a temperature of 398 K, of less than 1%. Such an adhesive can withstand thermal cycling from the high temperatures reached when illuminated by a high power light source to the low temperatures reached when the light source is off and the cold store cools the apparatus.

The apparatus may further comprise mounting means arranged to be usable to mount a light source adjacent a said window. Providing mounting means is advantageous in that the light source can be rigidly mounted to the apparatus, creating a robust and easy-to-install configuration.

The apparatus may further comprise fixing means configured to be usable to hold the hollow body in place when the apparatus is arranged to extend through the insulated wall of a cold store.

One or more of the surfaces of the light filtering and transmission apparatus through which light passes in use may have an antireflective coating. Preferably all of the surfaces have antireflective coatings. Providing antireflective coatings on the surfaces lying in the optical path of the apparatus between the light source and the interior of the cold store, in use, improves the overall efficiency of the apparatus.

Viewed from another aspect, the invention provides a lighting system for providing light to the interior of a cold storage unit, the lighting comprising: a light filtering and transmission apparatus according to any of the aforementioned arrangements; and a light source arranged to, in normal use, provide light to a said window of the light filtering and transmission apparatus.

The heat filtering means of the light filtering and transmission apparatus may be provided as or arranged adjacent the window of the hollow body on which the light source is, in normal use, first incident.

Viewed from yet another aspect, the invention provides use of a lighting system according to any of the aforementioned arrangements to light the interior of a cold store.

The lighting system according to any of the aforementioned arrangements is preferably arranged to provide light to the interior of a cold storage unit, wherein the light source is provided outside the cold storage unit, and wherein the lighting system is arranged such that the light filtering and transmission apparatus provides light from the light source to the interior of the cold storage unit in use.

The hollow body of the light filtering and transmission apparatus preferably extends in a bore in a wall/ceiling of the cold storage unit. A transparent fireproof cover is preferably provided on the inside of the cold store arranged to cover the bore. The fireproof cover may include a toughened glass or polycarbonate plate, which may be placed over the bore adjacent a window of the hollow body, and may be laminated with the window of the hollow body. The fireproof cover may be secured in place by a metal fixing such as a fixing ring provided around the cover and screwed into the wall/ceiling of the cold store, or may be screwed directly into the wall/ceiling of the cold store. A suitable sealant, such as a fire resistant sealant, like silicone sealant, may seal the cover around the bore. A fire resistant foam, such as an intumescent foam, may be provided in the bore surrounding the hollow body of the light filtering and transmission apparatus. These preferred arrangements, and in particular the provision of the fireproof cover, can enable the cold storage unit including the lighting system to retain or achieve a particular fire rating and safety certification.

Preferably the lighting system is flush with the wall/ceiling of the cold storage unit. Within this 'flush' arrangement, a small layer of material, such as a fireproof cover, may protrude from the wall/ceiling. This preferred arrangement ensures the whole lighting system assembly retains a low-profile in the cold store so that collision with and breakage of elements of the lighting system is unlikely, increasing safety. In addition, this arrangement presents no vertically-facing surfaces on which dust can collect, which provides a hygienic arrangement ideal for use in 'clean' cold stores, such as food storage and preparation areas.

Sealing means may be arranged to prevent water ingress into the bore from the outside of the cold storage unit.

Viewed from another aspect, the present invention provides a cold storage unit comprising a lighting system in accordance with any of the above mentioned arrangements, arranged to provide light to the interior of the cold storage unit.

Viewed from another aspect, the present invention provides a method of installing a lighting system in accordance with any of the aforementioned arrangements, to provide light to the interior of a cold storage unit, comprising: creating, from outside of the cold storage unit, a bore through a wall/ceiling of the cold storage unit dimensioned so as to accommodate the hollow body of the light filtering and transmission; inserting the hollow body of the light filtering and transmission into the bore from the interior of the cold storage unit; and arranging the light source in place outside the cold store to provide light to a said window of the light filtering and transmission apparatus.

This method of providing light to the interior of a cold store facilitates clean installation with minimal debris being produced in the interior of the cold store that cannot easily be contained, which may be important where the cold store is intended to provide a controlled, clean environment. The method also allows easy retrofitting of a highly efficient and powerful lighting system of the present invention to existing cold stores, during operation of the cold store. As the installation steps that need to be performed by persons located inside the cold store are few and simple, the installation can be achieved within the time allowed for persons to enter and remain in the cold store during operation, without having to increase the temperature of the cold store, or even having to switch off the refrigeration completely, which could spoil foodstuffs and increase operation costs significantly.

The method preferably also comprises a step of arranging a fireproof cover over the bore opening on the inside of the cold storage unit. The method preferably also comprises a step of arranging sealing means around the hollow body to prevent water ingress into the bore from the outside of the cold storage unit.

The above-described advantages of the first described aspect of the invention are also provided by the subsequently described aspects of the invention.

DESCRIPTION OF THE EMBODIMENTS

Certain preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a schematic side view of a cross-section of a first embodiment of a light filtering and transmission apparatus;

Figure 2 shows a schematic side view of a cross-section of a second embodiment of a light filtering and transmission apparatus, together with a light source;

Figure 3 shows a schematic side view of a cross-section of a cold storage unit incorporating a lighting system according to an embodiment of the invention; and

Figure 4 shows a schematic side view of a cross-section of a third embodiment of a light filtering and transmission apparatus arranged in situ in a cold store, together with a light source.

A light filtering and transmission apparatus 1 of a first embodiment of the invention 1 shown in Figure 1 includes a hollow tubular body 3, integrally formed and having a circular cross section. The tubular body 3 may be provided by an acrylic or polycarbonate material and may be formed by, for example, moulding, machining or extrusion. The tubular body has an axial length of between 450mm to 500mm and an external diameter of 60mm. Alternatively, both the diameter and length of the tube may be larger or smaller. The ends of the tubular body 3 are closed by first and second windows 5, 7 which hermetically seal the interior of the tubular body 3, with the internal surface of the tubular body 3 thereby defining a cavity 4. The cavity 4 is sealed in normal atmospheric conditions and thereafter evacuated using a non-return valve 11 to pump down or out-gas the cavity as much as is desired. The greater the degree of evacuation of the cavity 4, the more pronounced the advantageous effects of the invention. Alternatively the cavity may be sealed in an evacuated chamber.

The first window 5 and the second window 7 provide a direct line of sight for light to pass through the body. In normal use in a lighting system for a cold store, light from a light source (not shown) passes first through the first window 5, located distant from the interior of the cold store, and secondly through the second window 7, located proximal to (e.g. in the wall and/or ceiling of) the interior of the cold store.

Thus the first window 5 is provided as a light input window which, in normal use, is where light from an adjacent external light source (not shown) is first incident. The first window 5 is also provided as a heat filtering means. The first window 5 has a transmission function that varies across different wavelengths of light and is configured as desired so as to allow transmission of visible wavelengths of light from an adjacent light source into the cavity 4 and suppress transmission of infra-red and ultra-violet wavelengths of light into the cavity 4. The first window 5 preferably provides substantially zero transmission of thermal infra-red wavelengths of light. The heat filtering means of the first window 5 may be configured such that the non-transmitted wavelengths of light are absorbed thereat and/or reflected away. The first window 5 is made of 6mm thick toughened glass. The heat filtering means may be deposited on the surface of the first window 5 in one or more layers.

Alternatively the window material itself may provide the filtering effect.

Alternatively the heat filtering means may be provided separate from but adjacent to the first window 5.

The second window 7 is provided as a light output window and is a 6mm thick appropriately-shaped acrylic disc. Other window thicknesses and materials are of course possible and within the scope of the invention. The second window 7 is lightly frosted to diffuse light incident thereon and give a diffuse illumination of the interior of the cold store. The second window 7 may also be provided as a light- directing lens or may be provided merely as a transparent window. Alternatively, a separate diffuser or lens member may be provided adjacent to or on the second window 7 to diffuse and/or direct the light. Such separate lens/diffuser members are advantageous when provided with an apparatus having a second window 7 that is merely a transparent window. Any separate diffuser/lens may be mounted directly to the second window 7 or may be mounted to be spatially separated from the window. A separate lens/diffuser member mounting means (not shown) may be provided as part of the apparatus 1 for this purpose. Alternatively a fixative may be used to mount any diffuser/lens member.

Of course, for the windows 5, 7 other, non-circular, window shapes are within the scope of the invention. Such non-circular window shapes are particularly advantageous to seal the ends of the tubular body 3 where the tubular body 3 has a non-circular cross section.

The interior surface of the hollow tubular body 3 is coated with a highly reflective material 9 (for example by silvering) to guide light input at the first window 5 to be output at the second window 7 and to substantially prevent light losses along the length of the hollow body 3. Alternatively, the highly reflective material may be provided around the outer surface of the hollow body 3. The highly reflective material 9 may be deposited on the relevant surface of the body or may be separate from the body 3 and be merely located adjacent to the body 3 or be affixed thereto.

The light filtering and transmission apparatus 1 of the first embodiment may be located adjacent to the light output aperture of a light source. The light source may be provided in a separate fitting with the light filtering and transmission apparatus 1 being registered to it.

A light filtering and transmission apparatus 20 of a second embodiment of the invention shown in Figure 2 is identical to the first embodiment described above with the addition of a mounting means 21 (for example a light fixing) to receive a light source 23 in use. The mounting means 21 is rigidly connected to the first window 5 (and/or the hollow body 3) to locate the light source in the optimal position. Alternatively, the mounting means 21 may be formed integrally with the hollow body 3. Power input means for the light source 23 may also be provided with the mounting means 21, or may be separately provided.

Figure 3 shows a large cold store 30 having a lighting system 31 including a plurality of light filtering and transmission apparatus 20 according to the second embodiment of the invention. The cold store 30 has an internal wall 33 that defines an interior 34 of the cold store from which a refrigeration unit 32 extracts heat to cool the interior 34 to below the ambient temperature. A 250mm thick layer of thermal insulation 35 is provided surrounding the wall (i.e. wall or ceiling) 33 to limit the conduction of ambient heat into the interior 34.

The lighting system 31 is configured such that each light filtering and transmission apparatus 20 extends through the thermal insulation 35 to transmit visible light but little or no heat from a number of external light sources 23 to the interior 34 of the cold store 30. Each light filtering and transmission apparatus 20 is arranged such that the diffuse output second window 7 of each light filtering and transmission apparatus 20 is located in the internal wall (i.e. wall or ceiling) 33 of the cold storage unit 30. Each light filtering and transmission apparatus 20 then extends through the insulating material 35 such that its input first window 5 is located outside the insulating material 35 and the cold store 30. The light sources 23 are located externally to the cold store 30, away from the insulating layer 35 such that the heat transmission from the light sources 23 to the cold store, for example by conduction through the insulation, is substantially prevented.

In use, power is provided to the light sources 23 and the light filtering and transmission apparatus 20 acts to filter out infra-red and ultra-violet light produced by the light source and efficiently transmit substantially all of the remaining (visible) light entering the cavity 4 through the first window 5 of each light filtering and transmission apparatus 20 to the interior 34 of the cold storage unit, the second window 7 being such that the lighting system 30 efficiently provides a diffuse light to the interior 34. The lighting system 31 is such that heat produced by the external light sources 23 is substantially not transmitted to the interior 34 of the cold store and the refrigeration unit 32 therefore does not have to operate to remove that heat.

The light filtering and transmission apparatus of the invention may include multiple light sources, and may multiple input and output windows inputting and outpυtting light at different locations. The hollow body of the apparatus may be non-tubular. The hollow body may be configured such provide light transmission from an input to an output window by a non-direct line of sight.

Figure 4 shows a third embodiment of the invention in which the light filtering and transmission apparatus 40 includes a hollow tubular body 43 comprising a glass cylinder having windows 45, 47 covering the open ends of the glass cylinder 43. The windows 45, 47 are adhered to the rim of the glass cylinder 43 in a hermetically sealing fashion using a high strength, epoxy-based adhesive which can withstand thermal cycling and a wide range of temperatures. An example of such an adhesive is Master Bond EP21. To allow evacuation of the hollow body 43, the cylindrical wall thereof initially has a branch tube (not shown) extending from the cylindrical wall in communication with the cavity of the hollow body 43. After the windows 45, 47 have sealed the open ends of the hollow body 43, a pump is used to evacuate the chamber via the branch tube which is thereafter closed off to seal the evacuated hollow body 43 by pinching the opposing walls of the branch tube together close to the cylindrical wall of the hollow body 43. The branch tube is removed during the pinching.

Before evacuation, the inner surface of the cylindrical glass tube 43 is coated with a reflective layer of silvering 49 to guide light between the windows 45, 47 in use. Any appropriate silver coating process can be used.

The windows 45, 47 are provided as glass discs having a diameter matching the outer diameter of the glass cylinder 43. The windows may alternatively be provided as toughened glass or any other suitable, transparent, material. Both surfaces of the windows 45, 47 are provided with antireflective coatings to reduce light losses through the transmission system and increase the efficiency.

A protective tubular casing 50 having an internal diameter greater than the external diameter of the hollow body 43 is provided radially surrounding the hollow body 43 and a gap therebetween is filled with an expanding insulation foam 51. The casing 50 may be a suitable resin plastic based material, such as ABS, or a polycarbonate material. Polycarbonate discs, 51, 53 are provided adjacent windows 45, 47 to cover the open ends of the tubular casing 50. The polycarbonate discs, 52, 53 may be laminated with the windows 45, 47 and may have antireflective coatings on both surfaces. The casing 50, insulation foam 51, and polycarbonate discs 52, 53 protect the glass of the hollow body 43 and windows 45, 47 to reduce the likelihood of breakage thereof and also seal these components inside a durable casing such that even if the glass components were to break, no pieces of glass can reach outside the casing. This ensures that the illuminated space of the cold store remains a clean and controlled environment suitable for, e.g., food preparation.

A diffuser 55 is provided on the outer surface of the disc 53 to diffuse light inside the cold store and increase the breadth and angle of illumination. The diffuser 55 is preferably light shaping diffuser of the type produced by, for example, Luminit LLC of Torrance, CA, USA. The light shaping diffuser 55 is provided on a flexible polycarbonate sheet and has a relief structure replicated from a holographically recorded master which provides a randomised, non-periodic structure acting as randomised micro-lenslets. This gives a high transmission efficiency in the visible wavelengths of light of 90% or more, and the diffusion filter 55 can be selected to have a structure giving a desired angle of light diffusion from the light transmission and filtering apparatus 40. In this way, the diffusion filter 55 also acts as a divergent lens, which facilitates design of a lighting system for a cold store. The flexible polycarbonate diffuser sheet 55 can be mounted to the polycarbonate disc 53, giving a simple construction and keeping the profile of the assembly low in the cold store.

The light filtering and transmission apparatus 40 is installed into the wall/ceiling of a cold store by creating a bore in the insulation panel 57 from outside the cold store sized to accommodate the casing 50. The bore may be created by any suitable method, such as, for example, drilling or milling. The apparatus 40 is then inserted into the bore from inside the cold store. The polycarbonate window 53 has a diameter greater than the opening of the bore and has screw openings for receiving self-tapping screws which are used to fix the light filtering and transmission apparatus 40 to the insulation panel 57 in the wall/ceiling of the cold store.

Alternatively, a metal fixing ring (not shown) having screw openings for receiving self-tapping screws may be provided to surround the polycarbonate window 53 to fix the light filtering and transmission apparatus 40 to the insulation panel 57.

Any debris falling into the inside of the cold store from the creation of the bore is minimal and can be contained so that it does not freely enter the cold store. Further, the amount of time spent by an installation engineer inside the cold store is minimal, and so the installation can occur efficiently while the cold store is operational. The light filtering and transmission apparatus 40 is substantially flush with the insulation panel 57, with only the thickness of the polycarbonate disc 53 and diffuser 55 standing proud from the surface. This reduces the likelihood of any collision with the lighting system from moving items inside the cold store (e.g. carried by forklifts).

From above the insulation panel 57, an expanding, high density foam 59 is injected into the bore to surround the casing 50 to seal the bore and retain the thermal insulation of the cold store space. The foam 59 is preferably an intumescent foam to fire-proof the lighting system. Together with the polycarbonate window 57, the foam 59 preferably helps ensure a desired fire rating for the cold store is achieved. Alternatively, or in addition, a fire-proof sealant (not shown), such as a bead of silicone sealant, may be provided to seal the gap between the polycarbonate window 57 and the insulation panel 55.

A fixing collar 61, having an 'L'-shaped cross section is provided to surround the casing 50 and face the outer surface of the insulation panel 55 around the bore. The fixing collar 61 is fixed to the casing 50 by fixing screws 62 and thereby centres and/or aligns the light filtering and transmission apparatus 40 in the bore. The collar 61 seals the casing to the insulation panel water-tight together with beads 63, 64 of silicone sealant provided at the edges of the collar 61. In this way, standing water that can collect on the outer surface of the insulation panel 55 (e.g. as condensation) is prevented from getting into the bore and damaging the insulation panel.

A lightsource box 65 is fixed to the outer end of the light filtering and transmission apparatus 40 by a lightsource fixing collar 67 attached to the lightsource box 65 and is fixed about the casing 50 by fixing screws.

The lightsource box 65 includes a light source 69, which is preferably a high power and high efficiency metal halide lamp, and a reflector 71, such as a parabolic reflector, arranged to couple as much light as possible generated by the light source 69 into the window 45 of the light filtering and transmission apparatus. The light source 69 is provided power in a controlled fashion by control gear 73 so as to properly ignite and drive the light source 69. The control gear 73 may a ballast (not shown), such as an electronic ballast, and an ignitor (not shown). The control gear 73 is provided with a temperature sensor (not shown) and an internal thermal cut-out system to shut off the control gear 73 and the power supply to the light source 69 if the temperature of the control gear 73 and/or light source 69 exceeds a threshold temperature. An additional temperature sensor (not shown) may be provided inside the lightsource box 65 arranged to cut off the power supply from the control gear 73 in case the measured temperature reaches a second threshold temperature, which is lower than the threshold temperature of the control gear shut-off system. This secondary power cut-off system avoids damage to the control gear, which would be expensive to repair or replace.

The lightsource box 65 also includes a heat filtering means 75 provided as a bandpass filter arranged adjacent the window of the light filtering and transmission apparatus 40. The heat filtering means 75 is configured to substantially transmit visible wavelengths of light and substantially suppress, by absorption or reflection, infrared wavelengths of light and ultraviolet wavelengths of light emitted from the light source 69 and to prevent those suppressed wavelengths of light from entering the window 45 of the light filtering and transmission apparatus 40. Alternatively, the heat filtering means 75 may be provided as an infrared-blocking filter together with a separate ultraviolet-blocking filter. A fan 77 is arranged to cool the heat filtering means 75 and to prevent it from overheating, in use. The lightsource fixing collar 67 may include one or more ducts (not shown) such as slots around the collar 67 to permit drainage and removal of any water that may collect on the upper surface of the window 45 and disc 53 in use (for example by condensation when the light source is switched off). The fan 77 also assists with the removal of standing water and debris.

The heat filtering means 75, together with the evacuation of the hollow body 40 and the locating of the light source 69 outside the cold store, substantially prevents the transmission of heat from the light source 69 to the interior of the cold store. In addition, the locating of the light source 69 outside the cold store facilitates replacement of the light source without having to enter the cold store. The light filtering and transmission apparatus 40 enables these benefits by ensuring an efficient coupling of the light generated by the light source 69 to create a diffuse light in the interior of the cold store.