WO2007048181A1

WO2007048181A1 - A method of coupling light collector sheets to a light transfer component

Info

Publication number: WO2007048181A1
Application number: PCT/AU2006/001581
Authority: WO
Inventors: James Bruce Franklin; Geoffrey Burton Smith
Original assignee: Fluorosolar Systems Limited
Priority date: 2005-10-24
Filing date: 2006-10-24
Publication date: 2007-05-03
Also published as: AU2006308502A1

Abstract

The present invention provides a method of coupling light collector sheets to a light transfer coupler. Each light collector sheet has an end-surface that provides a sheet coupling surface. The method comprises coupling the sheet coupling surface of a first light collector sheet with a coupling surface of the light transfer coupler to form a first coupling. Further, the method comprises coupling the sheet coupling surface of a second light collector sheet with another coupling surface of the light transfer coupler to form a second coupling. At least one of the first and the second couplings is overlapped by a portion of the transfer coupler and the other coupling is overlapped by at least one of the light collector sheets.

Description

A METHOD OP COUPLING LIGHT COLLECTOR SHEETS TO A LIGHT

TRANSFER COMPONENT

Field of the Invention

The present invention broadly relates to a method of coupling light collector sheets to a light transfer component .

Background of the Invention

Electrical lighting systems are often very inefficient; usually more than 90% of the electrical energy is not converted into useful light. Sunlight, however, is freely available and attempts have been made to collect sunlight for illumination purposes.

US Patent 6059438 discloses a sunlight collecting and transmitting system. The disclosed system comprises three flat collector sheets. The three sheets are stacked on top of each other and are composed of a polymeric material that is doped with fluorescent dye molecules. The dye molecules absorb sunlight of a particular wavelength and subsequently emit fluorescent light having a slightly longer wavelength. A first sheet is doped with blue dye molecules, a second sheet is doped with green dye molecules and a third sheet is doped with red dye molecules. The generated fluorescent light is guided by total internal reflection within the collector sheets and white light can be generated by combining the blue, green and red fluorescent light. The fluorescent light generated by such stacks of light collector sheets may be guided into buildings to illuminate the interior of the buildings. For this purpose end-faces of the light collector sheets typically are connected to end-faces of un-doped light transfer sheets using a suitable coupling medium which establishes optical and mechanical connections. As indicated in US patent no. 6272265, optical connections which do not allow a continuous optical pathway between connected sheets may result in intensity losses and consequently the entire end-faces typically are connected by the coupling medium.

As the light collector sheets and the un-doped light transfer sheets typically have a combined length of many metres and a width of typically 1 to 100 cm, the one-by- one connection of the light collector sheets to light transfer sheets at their end-faces is a difficult task. Particular care needs to be taken that no coupling medium penetrates between adjacent side surfaces of adjacent light collector sheets. Such coupling medium between a first and a second light collector sheet typically would result in leaking of fluorescent light between the light collector sheets. For example, fluorescent light generated in the first light collector sheet may leak into the second light collector sheet. If that light has sufficient energy to be absorbed by dye molecules in the second light collector sheet, intensity loss and/or colour changes may occur. Consequently, the surfaces to which coupling medium may be applied to establish the connection are limited to end-faces which are relatively small and the connections are therefore of limited mechanical strength of the connection. To avoid the application of coupling medium at portions between side portions of the light collector sheets, the sheets are coupled one-by one.

Summary of the Invention

The present invention provides in a first aspect a method of coupling light collector sheets to a light transfer coupler, each light collector sheet having an end-surface that provides a sheet coupling surface, the method comprising: coupling the sheet coupling surface of a first light collector with a coupling surface of the light transfer coupler to form a first coupling; and coupling the sheet coupling surface of a second light collector sheet with another coupling surface of the light transfer coupler to form a second coupling; wherein at least one of the first and the second couplings is overlapped by a portion of the transfer coupler and the other coupling is overlapped by at least one of the light collector sheets.

Throughout this specification the meaning of the term "overlap" also includes that of the term "overlay" .

As at least one of the first and the second couplings are overlapped by a portion of the light transfer coupler and the other coupling is overlapped by at least one of the light collector sheets, the mechanical strength of the coupling typically is improved.

The light collector sheets typically have a rectangular cross-sectional shape. The sheets may be elongated and typically have a length of 0.1 - 5m, a width of 1 to 100cm and a thickness in the range of 0.5 -10mm. At least one of the light collector sheets may be stacked over another light collector sheet.

In one specific example, the second light collector sheet is doped with dye molecules that emit fluorescent light having a second range of wavelengths and the first light collector sheet is doped with dye molecules that absorb light having a first range of wavelengths that are shorter than those of the second range, in this case coupling typically is effected in a manner so that the first light collector sheet overlaps a coupling between the light transfer coupler and the second light collector sheet . In general, coupling typically is effected in a manner so that a first light collector sheet that is doped with dye molecules that emit fluorescent light having a shorter wavelength overlaps a coupling between the light transfer coupler and a second light collector sheet that is doped with dye molecules that emit fluorescent light having a longer wavelength. An additional coupling may then be effected at an overlapping portion between the first light collector sheet and the light transfer coupler, which increases mechanical strength and facilitates the coupling procedure. Because of the above- described arrangement of the light collector sheets, it can substantially be avoided that the additional coupling results in directing fluorescent light form the first light collector sheet into the second light collector sheet.

For example, the second light collector sheet may be doped with dye molecules that emit red fluorescent light and the first light collector may be doped with dye molecules that emit green fluorescent light. As the first light collector sheet overlaps a portion of the light transfer coupler, it can substantially be avoided that emitted green fluorescent light is directed into the second light collector sheet even if coupling is effected between the first light collector sheet and the light transfer coupler.

Using prior art methods, significant care needs to be taken to avoid coupling between side-portions of light collector sheets as this would result in intensity losses and/or colour changes. For this reason the couplings were established one-by one, sheet by sheet. This is especially cumbersome if the sheets are large and the joints are fragile. However, if the couplings are effected by the above-defined method, it is possible, and even advantageous, to allow coupling to from between side- portions of the light collector sheet and a light transfer coupler at each overlap and it is possible to couple a stack of the light collector sheets to the light transfer coupler typically without the need to dissemble the stack of the light collector sheets.

The method typically comprises effecting the coupling using a welding technique such as laser welding to establish mechanical and optical couplings. Coupling by welding may comprise the step of applying a coupling medium to the coupling surfaces.

It is to be appreciated that with the above-defined method any number of light collector sheets may be coupled to the light transfer component.

The light transfer coupler may have any number of coupling surfaces for coupling to a respective number of light collector sheets in a manner such that each coupling is overlapped by a portion of at least one light collector sheet or by a portion of the light transfer coupler.

For example, the light transfer coupler may have a height that substantially corresponds to a height of a stack of light collector sheets. The light transfer coupler typically comprises a plurality of steps, each step having a height and width that substantially corresponds to the height and width of one sheet coupling surface of one of the light collector sheets. In one specific variation, the light transfer coupler has two stepped portions which are positioned so that light received from one stack of coupled light collector sheets is guided to a stack of coupled light transfer sheets.

The present invention provides in a second aspect a method of coupling light collector sheets to light transfer sheets, each light collector sheet and each light transfer sheet having an end-surface which provides a sheet coupling surface, the method comprising: coupling the sheet coupling surface of a first light collector sheet with the sheet coupling surface of a first light transfer sheet to form a first coupling; and coupling the sheet coupling surface of a second light collector sheet with the sheet coupling surface of the first light transfer sheet to form a second coupling; wherein at least one of the first and the second couplings is overlapped by a portion of at least one light transfer sheets and the other coupling is overlapped by at least one of the light collector sheets.

The light collector sheets typically are arranged for emitting fluorescent light having differing wavelength ranges. Coupling typically is effected in a manner so that one of the light collector sheet that is doped with dye molecules that emit fluorescent light having a shorter wavelength overlaps a coupling between one of the light transfer sheets and a light collector sheet that is doped with dye molecules that emit fluorescent light having a longer wavelength.

It is to be appreciated that with the above-defined method any number of light collector sheets may be coupled to any number of light transfer sheets. The method typically comprises coupling the light transfer sheets to a corresponding number of light collector sheets. For example, a stack of light collector sheets may be coupled to a stack of light transfer sheets. Alternatively, the sheet coupling surface of at least one light transfer sheet may be coupled to a plurality of light transfer sheets. In this case the method typically comprises coupling each light collector sheet to a plurality of light transfer sheets. The light transfer sheets typically have a rectangular cross-sectional shape. The light transfer sheets may be elongated and typically have a length of 1 - 50 m, a width of 1 to 100 cm and a thickness in the range of 0.5 - 10 mm. At least one of the light transfer sheets may be stacked over another light transfer sheet.

The present invention provides in a third aspect a light transfer coupler for coupling a first stack of at least two light collector sheets to at least one light transfer component, the light transfer coupler comprising: at least two first coupling surfaces for. establishing first couplings with sheet coupling surfaces of the light ■ collector sheets in a manner so that each first coupling is overlapped by a portion of the light transfer coupler or by the, or at least one of the, light collector sheets; and at least one second coupling surface for establishing a second coupling with the coupling surface of the or each light transfer component.

The at least two first coupling surfaces typically are surfaces of steps. Each step typically has substantially the same height and width as the sheet coupling surface of a respective light collector sheet.

! In one specific embodiment of the present invention the second coupling surface is round or rounded and arranged for coupling to a light transfer component that has a round or rounded cross-sectional shape, such as an optical cable.

The second coupling surface also may be one of at least two second coupling surfaces for establishing second couplings and the or each light transfer component typically is one of a stack of light transfer sheets. The at least two second coupling surfaces typically are surfaces of steps .

The coupling surfaces of the coupler may be arranged so that the cross-sectional area in a direction perpendicular to a direction in which light in use is guided decreases. However, this typically results in light intensity losses and the coupling surfaces of the coupler typically are arranged so that the cross-sectional area in a direction perpendicular to a direction in which light in use is guided does not decrease. In one specific embodiment the cross-sectional area is substantially constant in the direction in which light in use is guided. The light transfer coupler may comprise two ends and the first coupling surfaces may be positioned at a first end and the or each second coupling surfaces may be positioned at the second end. In this case the light transfer coupler may comprise a first number of first coupling surfaces and a first number of second coupling surfaces. Alternatively, the light transfer coupler may comprise a first number of first coupling surfaces and a second number of second coupling surfaces, the second number being smaller or greater than the first number.

The , first and the second ends may be opposite ends. The light transfer coupler may also comprise more than two ends, such as three ends, and the first coupling surfaces may be positioned at a first end and the second coupling surfaces may be positioned at second and third ends. In this case the light transfer coupler typically is arranged for splitting light received at the first coupling surface to light transfer components that are in use coupled to the second coupling surfaces at the second and third ends . The light transfer coupler may comprise a bent portion which in use guides light received from coupled light collector sheets in an angled direction to coupled light transfer components. For example, the light transfer coupler may have a right angle bent (or may be bent by any other angle) between respective coupling surfaces.

The light transfer coupler may be composed of any suitable material, but typically is composed of polymethylmethacrylate (PMMA) .

An advantage of the light transfer coupler is that it can provide a precision interface that facilitates the coupling of a stack of light collector sheets to a pre- manufactured light transfer components assembly which may includes multiple light transfer components, protective jackets, end fittings, etc.

The present invention provides in a fourth aspect a light transfer coupler for coupling a first stack of at least two first light transfer components to at least one second light transfer component, the light transfer coupler comprising: at least two first coupling surfaces for establishing first couplings with coupling surfaces of respective first light transfer components so that each coupling is overlapped by a portion of the light transfer coupler or by the, or at least one of the, light first light transfer components; and at least one second coupling surface for establishing a second coupling with the coupling surface of the or each second light transfer component.

The present invention provides in a fifth aspect a light transfer component for coupling to a stack of at least two light collector sheets, the light transfer component comprising: at least two coupling surfaces for establishing couplings with sheet coupling surfaces of the light collector sheets in a manner so that each coupling is overlapped by a portion of the light transfer coupler or by the, or at least one of the, light collector sheets.

The invention will be more fully understood from the following description of specific embodiments of the invention. The description is provided with reference to the accompanying drawings .

Brief Description of the Drawings Figure 1 shows a side view of light collector sheets coupled to light transfer sheets by a method according to a specific embodiment of the present invention,

Figure 2 shows a side view of a light transfer coupler coupled to light collector sheets and light transfer sheets by a method according to a specific embodiment of the present invention,

Figure 3 shows a side view of light transfer coupler according to a further specific, embodiment of the present invention,

Figure 4 shows a side view of light transfer coupler according to another specific embodiment of the present invention, Figure 5 and 6 shows a side views of light transfer couplers coupled to light transfer sheets by a method according to an embodiment of the present invention and

Figure 7 shows a light transfer coupler according to another embodiment of the present invention.

Detailed Description of Specific Embodiments

Referring initially to Figure 1, a method of coupling light collector sheets to light transfer components according to a specific embodiment of the present invention is now described. In this embodiment light collector sheets 10, 12 and 14 are coupled to light transfer sheets 16, 18 and 20. The light collector sheets are doped with dye molecules that absorb sunlight and emit fluorescent light which is then guided inside each sheet by total internal reflection. For example, the light collector sheet 10 may be doped with dye molecules that emit blue fluorescent light, the light collector sheet 12 may be doped with dye molecules that emit green fluorescent light, and the light collector sheet 14 may be doped with dye molecules that emit red fluorescent light.

The light collector sheets 10, 12 and 14 are in this example composed of PMMA that is doped with the dye molecules and the light transfer sheets 16, 18 and 20 are composed of undoped PMMA. The light collector sheets 10, 12 and 14 typically are positioned at an exterior surface of a building and are arranged to collect sunlight. They are typically flat and may have a length of approximately one metre and a width of approximately 10 cm. The light collector sheets 10, 12 and 14 have sheet coupling surfaces 10a, 12a and 14a, which are coupled to light transfer sheets 16, 18 and 20 at sheet coupling surfaces 16a, 18a and 20a. The light transfer sheets 16, 18 and 20 are arranged to guide received fluorescent light, for example into the interior of the building to illuminate the interior of the building. In this example, the sheet coupling surfaces 10a, 12a and 14a have the same size as the sheet coupling surfaces 16a, 18a and 20a respectively. Coupling is effected by adhering respective coupling surfaces using a suitable infra-red absorptive material that is exposed to infra-red radiation emitted by a laser. Absorption of the infra-red radiation by the infra-red absorptive material results in generation of thermal energy which effects welding of the coupling surfaces. It is to be appreciated that in an alternative embodiment coupling may be effected by use of a suitable adhesive.

Each sheet coupling surface 10a, 12a, and 14a is overlapped by a portion of at least one of the light collector sheets 10, 12, 14, or the light transfer sheets 16, 18 or 20. Additional coupling may be effected between the adjacent side portion of the light collector sheet 12 and the light collector sheet 20 at portion 22 (which advantageously does not overlap collector sheet 14) , and between the light collector sheet 10 and the light transfer sheet 18 at portion 24 (which advantageously does not overlap collector sheet 12) . The additional coupling at the side portions increases the mechanical strength of the couplings of light collector sheets 10 and 12 to light transfer sheets 16 and 18.

It is advantageous to avoid any coupling between side-portions of adjacent light collector sheets, such as the portion 27 (between light collector sheets 12 and 14) and portion 25 (between light collector sheets 11 and 12) as this typically produces a loss in intensity of the fluorescent light and/or a colour change. However, it is possible to effect coupling between light collector sheets (10 and 12) and un-doped light transfer sheets (18 and 20) at portions 22 and 24 without intensity or colour disadvantages which makes assembly less critical and also improves the mechanical stability. It is also possible to effect coupling between the undoped light transfer sheets 16 and 18 at portion 26, and between the undoped light transfer sheets 18 and 20 at portion 28, without intensity or colour disadvantages which makes assembly less critical and also improves the mechanical stability. It is to be appreciated that in a variation of the embodiment illustrated in Figure 1 and described above, any number of light transfer components may be coupled to any number of light collector sheets in a manner such that each coupling is overlapped by a portion of at least one light transfer sheet and/or by a portion of at least one light collector sheet. For example, each light collector sheet may be coupled to two or more light transfer sheets. In this case the area of each sheet coupling surface of the light collector sheets typically corresponds to the combined cross-sectional area of the light transfer sheets that are coupled to the light collector sheet. For example, the light collector sheets may have half the width of the light collector sheets or half the thickness of the light collector sheets. In this case typically two light transfer sheets typically are coupled side-by side or on top of ach other, respectively, to each light collector sheet . Further, it is to be appreciated that the light transfer sheets and the light collector sheets that are coupled may have any suitable size.

Figure 2 shows a light transfer coupler according to a specific embodiment of the present invention. The light transfer coupler 30 is coupled to ^• light collector sheets 12, 14 and to light transfer sheets 16 and 18. In this embodiment the light transfer coupler 30 is coupled to the light collector sheets 12, 14 and to the light transfer sheets 16 and 18 at coupling surfaces 30a, 30b, 30c and 3Od. The coupling surfaces 30a, 30b, 30c and 3Od abut against sheet coupling surfaces 12a, 14a, 16a and 18a, respectively, and coupling is effected by a suitable laser welding using the procedure described in the context of Figure 1. Further, coupling is effected at areas 32

(which advantageously does not overlap collector sheet 14) and at areas 34 and 35. It is advantageous that the coupling is effected at areas 34 and 35 as this improves the strength of the joint for light transfer sheet 18. The additional coupling at area 32 increases the mechanical strength of the couplings of light collector sheets 12 to light transfer sheet 16. A mechanical connection to light collector sheet 14 may for example be improved by carefully clamping the light collector sheet 14 to light collector sheets 12 in a manner so that no optical path is established between the clamped light collector sheets or otherwise use the light collector sheet 12 to mechanically support the light collector sheet 14. In this embodiment the light transfer coupler 30 is composed of PMMA.

In the described embodiments the cross-sectional area of the light transfer medium is equal to or greater than the cross-sectional area of the collector sheets.

It is to be appreciated that the light transfer coupler 30 may, in variations of the embodiment shown in Figure 2, have any number of coupling surfaces for coupling to any number of light transfer sheets. For example, the light transfer coupler may have two legs with light transfer sheets in use being coupled to coupling surfaces at ends of the legs .

Figure 3 shows a light transfer coupler 40 which is similar to the light transfer coupler 30 shown in Figure 2 and has coupling surfaces 40a, 40b, 40c, 4Od and 40e for coupling to the sheet coupling surfaces of light transfer sheets and light collector sheets or further light transfer sheets. Figure 4 shows a light transfer coupler according to a further embodiment of the present invention. The light coupler 50 comprises a right-angle bend and is arranged so that light is guided from light collector sheets coupled to the light transfer coupler 50 in one plane to light transfer sheets coupled to the light transfer coupler in a perpendicular plane. The light transfer coupler 50 comprises coupling surfaces 50a, 50b, 50c, 5Od and 5Oe, and functions otherwise in the same manner as the light transfer coupler 40 discussed above. It is to be appreciated that in variations of the embodiment shown in Figure 4 the light transfer coupler may be arranged for guiding light received from coupled light collector or transfer sheets to other coupled light transfer sheets having any angular orientation relative to the light transfer sheets from which the light is received.

Figure 5 shows a light transfer coupler 60 according to a further embodiment of the present invention. The light transfer coupler 60 has coupling surfaces 60a to 6Oe and is arranged for coupling three light transfer sheets (not shown) to two light transfer sheets 62 and 64. The light transfer sheets 62 and 64 have sheet coupling surfaces 62a and 64a which are coupled to respective coupling surfaces of the light transfer coupler 60.

Further, coupling is effected between the light transfer sheets 62 and 64 at area 66.

The light transfer sheets 62 and 64 are coupled to respective light collector sheets 68 and 70, which have coupling surfaces 68a and 70a at which coupling is effected by butt-joints to respective coupling surfaces 62b and 64b of the light transfer components 62 and 64.

Figure 6 shows an embodiment that is related to that shown in Figure 5. The shown light transfer coupler 70 has coupling surfaces 60a to 6Oe and is arranged for coupling three light transfer sheets (not shown) to two light transfer sheets 72 and 74. The coupling surfaces 7Oe and 70 d are located in a common plane. The light transfer sheets 72 and 74 have sheet coupling surfaces 72a and 74a which are coupled to respective coupling surfaces of the light transfer coupler 70. Further, coupling is effected between the light transfer sheets 72 and 74 at area 76.

The light transfer sheets 72 and 74 are coupled to respective light collector sheets 68 and 70, which have sheet coupling surfaces 68a and 70a at which coupling is effected by butt-joints to respective coupling surfaces 72b and 74b of the light transfer components 72 and 74.

Figure 7 shows a light transfer coupler 80 according to a further embodiment of the present invention. The light transfer coupler 80 is arranged for coupling light transfer or light collector sheets to an optical cable. The light transfer coupler 80 comprises a flat portion 81 having in this embodiment three coupling surfaces 80a, 80b and 80c for coupling to three light collector sheets. The light transfer coupler 80 has an intermediate hollow and rounded portion 82 and a solid round end 84. The end 84 has a round coupling surface 8Od for coupling to an optical cable. Coupling may be effected in any suitable manner, and typically is effected using laser welding in the above-described manner. It is to be appreciated that in variations of the described embodiment the light transfer coupler 80 may take any other suitable form. For example, the end 84 may not necessarily be solid, the portion 81 may not necessarily be flat and the light transfer coupler 80 may be arranged for coupling any number of light transfer or collector sheets to any number of optical cables. Although the invention has been described with reference to particular examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms. For example, coupling surfaces may not be planar surfaces, but may have any suitable shape and may be arranged for any type of coupling including for example scarf butt joints, double butt lap joints or tongue and groove joints. Further, the light transfer coupler may be provided in form of a light transfer component that is arranged for coupling to light collector sheets but does not have coupling surfaces for coupling to light transfer components. The coupling between light collector sheets and light transfer components may also be made by other mean other than coupling mediums, such as chemical welding or laser welding.

The reference that is being made to prior patent US 6059438 does not constitute an admission that that reference forms a part of the common general knowledge of a skilled person.

Claims

The Claims :

1. A method of coupling light collector sheets to a light transfer coupler, each light collector sheet having an end-surface that provides a sheet coupling surface, the method comprising: coupling the sheet coupling surface of a first light collector sheet with a coupling surface of the light transfer coupler to form a first coupling; and coupling the sheet coupling surface of a second light collector sheet with another coupling surface of the light transfer coupler to form a second coupling; wherein at least one of the first and the second couplings is overlapped by a portion of the transfer coupler and the other coupling is overlapped by at least one of the light collector sheets.

2. The method of claim 1 wherein coupling is effected in a manner so that a first light collector sheet that is doped with dye molecules that emit fluorescent light having a shorter wavelength overlaps a coupling between the light transfer coupler and a second light collector sheet that is doped with dye molecules that emit fluorescent light having a longer wavelength.

3. The method of claim 2 wherein an additional coupling is effected at an overlapping portion between the first light collector sheet and the light transfer coupler.

4. The method of claim 3 wherein the additional coupling is effected so that it is substantially avoided that in use fluorescent light from the first light collector sheet is directed into the second light collector sheet.

5. The method of any one of the preceding claims wherein the light collector sheets have a rectangular cross- sectional shape.

6. The method of any one of the preceding claims wherein at least one of the light collector sheets is stacked over another light collector sheet.

7. The method of any one of the preceding claims comprising effecting coupling using a welding technique.

8. The method of claim 7 wherein the coupling comprises the step of applying a coupling medium to the coupling surfaces.

9. The method of any one of the preceding claims wherein the light transfer coupler has a height that substantially corresponds to a height of a stack of light collector sheets.

10. The method of any one of the preceding claims wherein the light transfer coupler comprises a plurality of steps, each step having a height and width that substantially corresponds to the height and width of one sheet coupling surface of one of the light collector sheets.

11. A method of coupling light collector sheets to light transfer sheets, each light collector sheet and each light transfer sheet having an end-surface which provides a sheet coupling surface, the method comprising: coupling the sheet coupling surface of a first light collector sheet with the sheet coupling surface of a first light transfer sheet to form a first coupling; and coupling the sheet coupling surface of a second light collector sheet with the sheet coupling surface of the first light transfer sheet to form a second coupling; wherein at least one of the first and the second couplings is overlapped by a portion of at least one light transfer sheets and the other coupling is overlapped by at least one of the light collector sheets.

12. The method of claim 11 wherein the light collector sheets arranged for emitting fluorescent light having differing wavelength ranges and wherein coupling is effected in a manner so a first light collector sheet that is doped with dye molecules that emit fluorescent light having a shorter wavelength overlaps a coupling between one of the light transfer sheets and a second light collector sheet that is doped with dye molecules that emit fluorescent light having a longer wavelength.

13. The method of claim 12 wherein an additional coupling is effected at an overlapping portion between the first light collector sheet and one of the light transfer sheets .

14. The method of claim 13 wherein the additional coupling is effected so that it is substantially avoided that in use fluorescent light from the first light collector is directed into the second light collector sheet .

15. The method of any one of claims 11 to 14 comprising coupling the light transfer sheets to a corresponding number of light collector sheets.

16. The method of any one of claims 11 to 15 comprising coupling a stack of light collector sheets to a stack of light transfer sheets.

17. The method of any one of 11 to 14 comprising coupling the sheet coupling surface of at least one light transfer sheet to a plurality of light transfer sheets.

18. The method of any one of claims 11 to 17 wherein the light transfer sheets have a rectangular cross- sectional shape .

19. The method, of any one of claims 11 to 18 wherein at least one of the light transfer sheets is stacked over another light transfer sheet.

20. A light transfer coupler for coupling a first stack of at least two light collector sheets to at least one light transfer component, the light transfer coupler comprising: at least two first coupling surfaces for establishing first couplings with sheet coupling surfaces of the light collector sheets in a manner so that each first coupling is overlapped by a portion of the light transfer coupler or by the, or at least one of the, light collector sheets; and at least one second coupling surface for establishing a second coupling with the coupling surface of the or each light transfer component.

21. The light transfer coupler of claim 20 wherein the at least two first coupling surfaces are surfaces of steps.

22. The light transfer coupler of claim 21 wherein each step has substantially the same height and width as the sheet coupling surface of a respective light collector sheet .

23. The light transfer coupler of any one of claims 20 to 22 wherein the second^" coupling surface is rounded and arranged for coupling to a light transfer component that has a round or rounded cross-sectional shape.

24. The light transfer coupler of any one of claims 20 to 22 wherein the second coupling surface is one of at least two second coupling surfaces for establishing second couplings and the or each light transfer component is one of a stack of light transfer sheets.

25. The light transfer coupler of claim 24 wherein the at least two second coupling surfaces are surfaces of steps.

26. The light transfer coupler of any one of claims 20 to 24 being arranged so that the cross-sectional area in a direction perpendicular to a direction in which light in use is guided does not decrease.

27. The light transfer coupler of any one of claims 20 to

26 wherein the cross-sectional area is substantially constant in the direction in which light in use is guided.

28. The light transfer coupler of any one of claims 20 to

27 wherein coupling areas of respective coupling surfaces are substantially the same.

29. The light transfer coupler of any one of claims 20 to 28 comprising two ends and the first coupling surfaces is positioned at a first end and the or each second coupling surfaces is positioned at the second end.

30. The light transfer coupler of claim 29 comprising a first number of first coupling surfaces and a first number of second coupling surfaces.

31. The light transfer coupler of claim 29 comprising first number of first coupling surfaces and a second number of second coupling surfaces, the second number being smaller or greater than the first number.

32. The light transfer coupler of any one of claims 29 to 31 wherein the first and the second ends are opposite ends .

33. The light transfer coupler of any one of claims 29 to 31 comprising more than two ends.

34. The light transfer coupler of claim 33 arranged for splitting light received at the first coupling surface to light transfer components that are in use coupled to the ₍ second coupling surfaces at the second and third ends.

35. The light transfer coupler of any one of claims 20 to 34 comprising a bent portion which in use guides light received from coupled light collector sheets in an angled direction to coupled light transfer components.

36. A light transfer coupler for coupling a first stack of at least two first light transfer components to at least one second light transfer component, the light transfer coupler comprising: at least two first coupling surfaces for establishing first couplings with coupling surfaces of respective first light transfer components so that each coupling is overlapped by a portion of the light transfer coupler or by the, or at least one of the, light first light transfer components; and at least one second coupling surface for establishing a second coupling with the coupling surface of the or each second light transfer component.

37. A light transfer component for coupling to a stack of at least two light collector sheets, the light transfer component comprising: at least two coupling surfaces for establishing couplings with sheet coupling surfaces of the light collector sheets in a manner so that each coupling is overlapped by a portion of the light transfer coupler or by the, or at least one of the, light collector sheets.