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Title:
A PLANAR LED LIGHT SOURCE MODULE
Document Type and Number:
WIPO Patent Application WO/2019/154930
Kind Code:
A1
Abstract:
A light emitting diode, LED, light source module for a luminaire. The LED light source module comprises a PCB (9), at least one row of LEDs mounted on the PCB (9); a plurality of optical layers coupled to the LEDs for emitting a surface of light; and a housing (3). The optical layers comprise: a light guide plate subassembly comprising a light guide plate layer (5); a reflector film layer (6); and a diffuser layer (4). The light guide plate subassembly is mechanically mounted to the housing (3).

Inventors:
HANBURY, Matthew (37 Cloncurry House Spencer Dock, North WallDublin, D01 E186, D01 E186, IE)
Application Number:
EP2019/053046
Publication Date:
August 15, 2019
Filing Date:
February 07, 2019
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
LIGHTLY TECHNOLOGIES LIMITED (37 Cloncurry House Spencer Dock, North WallDublin, D01 E186, D01 E186, IE)
International Classes:
F21V17/16; F21V8/00; F21V23/00; F21Y103/10; F21Y115/10
Domestic Patent References:
WO2018029285A12018-02-15
Foreign References:
CN206669651U2017-11-24
CN205504708U2016-08-24
CN206539952U2017-10-03
CN206160058U2017-05-10
CN206943951U2018-01-30
Attorney, Agent or Firm:
REEDY, Orlaith (PurdyLucey Intellectual Property 6-7 Harcourt Terrace, Dublin, D02 FH73, D02 FH73, IE)
Download PDF:
Claims:
Claims

1. A light emitting diode, LED, light source module for a luminaire comprising: a printed circuit board, PCB;

at least one row of LEDs mounted on the PCB;

a plurality of optical layers coupled to the LEDs for emitting a surface of light; and

a housing;

wherein the optical layers comprise a light guide plate subassembly comprising:

a light guide plate layer;

a reflector film layer; and

a diffuser layer; wherein the light guide plate subassembly is mechanically mounted to the housing.

2. The LED light source module of Claim 1 , wherein the light guide plate subassembly is mechanically mounted to the housing by means of a snap-fit connection.

3. The LED light source module of Claim 2, wherein the snap-fit connection comprises at least one snap fit feature located on one edge of the light guide plate subassembly adapted to mate with a complimentary notch located on the corresponding side of the housing.

4. The LED light source module of Claim 3, wherein each snap fit feature is located on an edge of the light guide plate subassembly which is perpendicular to the sides of the module on which the LEDs are located.

5. The LED light source module of Claim 4, wherein the snap-fit connection comprises a first pair of spaced apart snap fit features located on one edge of the light guide plate subassembly adapted to mate with a complimentary first pair of spaced apart notches located on the corresponding side of the housing, and a second pair of spaced apart snap fit features located on a second edge opposite the first edge of the light guide plate subassembly adapted to mate with a complimentary second pair of spaced apart notches located on the corresponding side of the housing.

6. The LED light source module of any of Claims 3 to 5, wherein each snap-fit feature comprises a cantilever snap-fit feature.

7. The LED light source module of any of Claims 1 to 6, wherein the diffuser layer and the reflector film layer are directly attached to the light guide plate layer in the light guide plate subassembly.

8. The LED light source module of Claim 7, wherein the diffuser layer and the reflector film layer are directly attached to the light guide plate layer by adhesive means.

9. The LED light source module of Claim 8, wherein the adhesive means comprises a double-sided adhesive tape located around the perimeter of the light guide plate layer.

10. The LED light source module of Claim 8, wherein the adhesive means comprises a layer of optically clear adhesive.

1 1 . The LED light source module of any of the preceding claims, wherein the light guide plate layer is fabricated from one of: acrylic (poly methyl methacrylate) or high density polyethylene and the reflector film layer, and the diffuser layer are fabricated from one of: acrylic, polyester and polyethylene terephthalate (PET).

12. The LED light source module of any of the preceding claims, wherein the housing comprises an internal rim, and wherein the module further comprises an optical transparent protective layer and a pressure sensitive adhesive for attaching the optical transparent protective layer to the internal rim of the housing.

13. The LED light source module of Claim 12, further comprising a BEF layer, wherein the BEF layer is mounted to the optical transparent protective layer.

14. The LED light source module of Claim 12, wherein the edges of the housing are flush with the optical transparent protective layer for direct mounting of the module onto a surface.

15. The LED light source module of any of the preceding claims, further comprising an attachment means for mounting the module to a surface.

16. The LED light source module of Claim 15, wherein the attachment means comprises a thermal conductive adhesive film attachable to the back film of the housing.

17. The LED light source module of Claim 15, wherein the attachment means comprises a stretch release tape attachable to the housing.

18. The LED light source module of Claim 15, when dependent on claim 12, wherein the attachment means comprises an optically clear adhesive film attachable to the optical transparent protective layer.

19. The LED light source module of any of the preceding claims, wherein the housing is fabricated from one of: polycarbonate, high density polyethylene or polypropylene.

20. The LED light source module of any of the preceding claims, wherein the PCB comprises a flexible PCB.

21. The LED light source module of any of the preceding claims wherein the at least one row of LEDs comprises a plurality of ultra-thin LEDs.

22. The LED light source module of any of the preceding claims, wherein the thickness of the module is less than 4.0 mm.

23. The LED light source module of any of the preceding claims, wherein the module comprises a recessed groove for receiving wiring for the module.

24. The LED light source module of Claim 23, wherein the wiring is configurable to emerge from the recessed groove diagonally from a corner of the housing and/or coincident to an edge of the housing and/or perpendicular to the module.

25. The LED light source module of any of the preceding claims, wherein each optical layer comprises one or more low friction thin films.

26. The LED light source module of Claim 12, wherein the wiring for the module is configurable such that it follows a path around the edge of the housing and passes through the internal rim.

27. The LED light source module of any of the preceding claims, further comprising a BEF layer.

28. The LED light source module of Claim 27, wherein the BEF layer is mounted to the light guide plate subassembly.

29. The LED light source module of Claim 12, wherein the internal rim is fabricated by means of an injection molding process as part of the housing.

30. The LED light source module of Claim 12, wherein the internal rim is fabricated by means of a silkscreen printing process on one of the plurality of optical layers.

31. A method for fabricating a light emitting diode, LED, light source module for a luminaire comprising: mounting at least one row of LEDs to a printed circuit board, PCB, to form a LED subassembly;

mounting the LED subassembly to a housing; and

mechanically mounting a light guide plate subassembly to the housing;

wherein the light guide plate subassembly comprises a light guide plate layer, a reflector film layer and a diffuser layer.

32. The method of Claim 31 , wherein the mechanical mounting of the light guide plate subassembly to the housing comprises mating at least one snap fit feature located on the edge of the light guide plate subassembly to a complimentary notch located on the corresponding side of the housing.

33. The method of Claim 31 or Claim 32, further comprising sealing the housing with a back film.

34. The method of any of Claims 31 to 33, further comprising attaching an optical transparent protective layer to the housing.

35. The method of any of claims 31 to 34, further comprising assembling the light guide plate subassembly by directly attaching the diffuser layer and the reflector film layer to the light guide plate layer.

36. The method of Claim 35, further comprising attaching the diffuser layer and the reflector film layer to the light guide plate layer by adhesive means.

37. The method of Claim 36, wherein the adhesive means comprises a double sided adhesive tape located around the perimeter of the light guide plate layer.

38. The method of Claim 36, wherein the adhesive means comprises a layer of optically clear adhesive.

Description:
Title

A planar LED light source module

Field

The present invention relates to a LED light source module for a luminaire. More particularly, the invention relates to providing a LED light source module for producing a flat surface of white light.

Background

There has been much research into the development of light sources which produce a surface of white light for a luminaire, instead of the more conventional point light sources, such as LED, incandescent and HID lamps (more commonly referred to as bulbs by consumers). One known technology achieves this through the creation of a square array of light emitting diodes (LEDs) mounted on a PCB. A mixing chamber then mixes and converges the LED light, while a diffuser reduces the glare from individual LEDs and provides a uniform panel luminance. However, this design suffers from the drawback that it requires a deep luminaire (typically 3-8cm in depth), due to a considerable volume being required by the mixing chamber.

Another technique makes use of edge-lit LED technology to create such a light source. However, this approach also requires a thick luminaire, and thus its use is limited to larger scale recessed luminaires and backlighting applications, such as for TVs and PC monitors. Furthermore, it requires the fabrication of a complete luminaire. Thus, it is not possible to create new luminaire designs using this technology.

It is an object of the present invention to provide a LED light source which produces a surface of white light which overcomes at least one of the above mentioned problems. Summary

According to the invention there is provided, as set out in the appended claims, a light emitting diode, LED, light source module for a luminaire comprising:

a printed circuit board, PCB;

at least one row of LEDs mounted on the PCB;

a plurality of optical layers coupled to the LEDs for emitting a surface of light; and

a housing;

wherein the optical layers comprise a light guide plate subassembly comprising:

a light guide plate layer;

a reflector film layer; and

a diffuser layer; wherein the light guide plate subassembly is mechanically mounted to the housing.

In one embodiment, the light guide plate subassembly is mechanically mounted to the housing by means of a snap-fit connection.

In one embodiment, the snap-fit connection comprises at least one snap fit feature located on one edge of the light guide plate subassembly adapted to mate with a complimentary notch located on the corresponding side of the housing.

In one embodiment, each snap fit feature is located on an edge of the light guide plate subassembly which is perpendicular to the sides of the module on which the LEDs are located.

In one embodiment, the snap-fit connection comprises a first pair of spaced apart snap fit features located on one edge of the light guide plate subassembly adapted to mate with a complimentary first pair of spaced apart notches located on the corresponding side of the housing, and a second pair of spaced apart snap fit features located on a second edge opposite the first edge of the light guide plate subassembly adapted to mate with a complimentary second pair of spaced apart notches located on the corresponding side of the housing. In one embodiment, each snap-fit feature comprises a cantilever snap-fit feature.

In one embodiment, the diffuser layer and the reflector film layer are directly attached to the light guide plate layer in the light guide plate subassembly.

In one embodiment, the diffuser layer and the reflector film layer are directly attached to the light guide plate layer by adhesive means.

In one embodiment, the adhesive means comprises a double sided adhesive tape located around the perimeter of the light guide plate layer.

In one embodiment, the adhesive means comprises a layer of optically clear adhesive.

In one embodiment, the light guide plate layer is fabricated from one of: acrylic (poly methyl methacrylate), high density polyethylene and the reflector film layer, and the diffuser layer are fabricated from one of: acrylic, polyester and polyethylene terephthalate (PET).

In one embodiment, the housing comprises an internal rim, and wherein the module further comprises an optical transparent protective layer and a pressure sensitive adhesive for attaching the optical transparent protective layer to the internal rim of the housing.

In one embodiment, the module further comprises a BEF layer, wherein the BEF layer is mounted to the optical transparent protective layer.

In one embodiment, the edges of the housing are flush with the optical transparent protective layer for direct mounting of the module onto a surface.

In one embodiment, the attachment means comprises a thermal conductive adhesive film attachable to the back film of the housing. In one embodiment, the attachment means comprises a stretch release tape attachable to the housing.

In one embodiment, the attachment means comprises an optically clear adhesive film attachable to the optical transparent protective layer.

In one embodiment, the housing is fabricated from one of: polycarbonate, high density polyethylene or polypropylene.

In one embodiment, the PCB comprises a flexible PCB.

In one embodiment, the at least one row of LEDs comprises a plurality of ultra- thin LEDs.

In one embodiment, the thickness of the module is less than 4.0 mm.

In one embodiment, the module comprises a recessed groove for receiving wiring for the module.

In one embodiment, the wiring is configurable to emerge from the recessed groove diagonally from a corner of the housing and/or coincident to an edge of the housing and/or perpendicular to the module.

In one embodiment, each optical layer comprises one or more low friction thin films.

In one embodiment, the wiring for the module is configurable such that it follows a path around the edge of the housing and passes through the internal rim.

In one embodiment, the module further comprises a BEF layer.

In one embodiment, the BEF is mounted to the light guide plate subassembly. In one embodiment, the internal rim is fabricated by means of an injection molding process on the housing.

In one embodiment, the internal rim is fabricated by means of a silkscreen printing process on one of the plurality of optical layers.

According to another embodiment of the invention there is provided a method for fabricating a light emitting diode, LED, light source module for a luminaire comprising:

mounting at least one row of LEDs to a printed circuit board, PCB, to form a LED subassembly;

mounting the LED subassembly to a housing; and

mechanically mounting a light guide plate subassembly to the housing;

wherein the light guide plate subassembly comprises a light guide plate layer, a reflector film layer and a diffuser layer.

In one embodiment, the mechanical mounting of the light guide plate subassembly to the housing comprises mating at least one snap fit feature located on the edge of the light guide plate subassembly to a complimentary notch located on the corresponding side of the housing.

In one embodiment, the method further comprises sealing the housing with a back film.

In one embodiment, the method further comprises attaching an optical transparent protective layer to the housing.

In one embodiment, the method further comprises assembling the light guide plate subassembly by directly attaching the diffuser layer and the reflector film layer to the light guide plate layer.

In one embodiment, the method further comprises attaching the diffuser layer and the reflector film layer to the light guide plate layer by adhesive means. In one embodiment, the adhesive means comprises a double sided adhesive tape located around the perimeter of the light guide plate layer. In one embodiment, the adhesive means comprises a layer of optically clear adhesive.

According to another embodiment of the invention there is provided a light emitting diode, LED, light source module for a luminaire comprising:

a printed circuit board, PCB;

at least one row of LEDs mounted on the PCB;

a plurality of optical layers coupled to the LEDs for emitting a surface of light and

a housing;

wherein each optical layer comprises one or more low friction thin films such that the optical layers are slidable with respect to one another when bent.

In one embodiment, the optical layers comprise:

a light guide plate layer;

a reflector film layer;

a diffuser layer; and

a brightness enhancement film, BEF layer.

In one embodiment, the light guide plate layer is fabricated from one of: Acrylic (Poly Methyl Methacrylate) or high density polyethylene and each of the reflector film layer, the diffuser layer and the BEF layer are fabricated from one of: acrylic, polyester and polyethylene terephthalate (PET).

In one embodiment, the housing comprises an internal rim, and wherein the module further comprises a pressure sensitive adhesive for attaching the BEF to the internal rim of the housing. In one embodiment, the edges of the housing are flush with the BEF for direct mounting of the module onto a surface.

In one embodiment, the LED light source module further comprises an attachment means for mounting the module to a surface.

In one embodiment, the attachment means comprises a thermal conductive adhesive film attachable to the back film of the housing.

In one embodiment, the attachment means comprises a stretch release tape attachable to the housing.

In one embodiment, the attachment means comprises an optically clear adhesive film attachable to the BEF.

In one embodiment, the housing comprises a flexible plastic.

In one embodiment, the housing has a Young Modulus in the range of 0.1 to 2.0 GPa, and preferably between 0.2GPa to 1.OGPa.

In one embodiment, the housing is fabricated from one of: polycarbonate, high density polyethylene or polypropylene.

In one embodiment, the PCB comprises a flexible PCB.

In one embodiment, the flexible PCB comprises a PCB provided with plurality of slots to improve flexibility.

In one embodiment, the at least one row of LEDs comprises a plurality of ultra- thin LEDs.

In one embodiment, the thickness of the module is less than 4.0 mm.

In one embodiment, the thickness of the module is 3.2mm. In one embodiment, the module comprises an x axis and a y axis, and wherein the module is bendable about one or both of its x and y axes.

In one embodiment, the module comprises a recessed groove for receiving wiring for the module.

In one embodiment, the wiring is configurable to emerge from the recessed groove diagonally from a corner of the housing and/or coincident to an edge of the housing and/or perpendicular to the module.

According to another aspect of the invention there is provided, a light emitting diode, LED, light source module for a luminaire comprising:

a printed circuit board, PCB;

at least one row of LEDs mounted on the PCB;

a plurality of optical layers coupled to the LEDs for emitting a surface of light and

a housing;

wherein the optical layers are slidable with respect to one another when bent.

In one embodiment, the light guide plate layer is coupled to the LEDs by an adhesive means.

The adhesive means comprises a light reflective adhesive film attached between the LED subassembly and the light guide plate layer.

In one embodiment, the wiring for the module is configurable such that it follows a path around the edge of the housing and passes through the internal rim.

In one embodiment, the module further comprises an optically transparent protective layer mounted to the BEF layer.

In one embodiment, the internal rim is fabricated by means of an injection molding process on the housing. In one embodiment, the internal rim is fabricated by means of a silkscreen printing process on one of the plurality of optical layers. According to another embodiment of the invention there is provided a light emitting diode, LED, light source module for a luminaire comprising:

a printed circuit board, PCB;

at least one row of LEDs mounted on the PCB;

a plurality of optical layers coupled to the LEDs for emitting a surface of light; an optical transparent layer; and

a housing;

wherein the optical layers comprise a light guide plate subassembly comprising:

a light guide plate layer;

a reflector film layer; and

a diffuser layer; wherein the light guide plate subassembly is mechanically mounted to the housing.

Brief Description of the Drawings

The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which :-

Figure 1 shows a perspective view of the LED light source module of the invention;

Figure 2 shows an exploded view of the light source module of Figure 1 ;

Figure 3 shows a section through the light source module of Figure 1 ;

Figure 4 shows one embodiment of a recessed groove provided on the housing of the light source module for the wiring;

Figure 5 shows one configuration of the wiring in the recessed groove;

Figure 6 shows an alternative configuration of the wiring in the recessed groove; Figure 7 shows another alternative configuration of the wiring in the recessed groove; Figure 8 shows a view of one exemplary configuration of the wiring within the light source module of Figure 1 ;

Figure 9 shows a cross section of the light guide plate subassembly of the LED light source module;

Figure 10 shows an exploded view of the components of the module prior to final assembly;

Figure 1 1 shows an exploded view of the light guide plate subassembly positioned above the housing with the snap-fit features of the light guide plate subassembly aligned for mating with their corresponding notches on the housing; Figure 12 shows a detailed perspective view of a notch in the housing which is adapted to receive a snap fit feature of the light guide plate subassembly; and Figure 13 shows a detailed top view of one snap-fit feature of the light guide plate subassembly mated with its corresponding notch on the housing.

Detailed Description of the Drawings

The present invention provides a LED light source module for a luminaire that produces white light from a surface which is flat and ultra-thin.

In accordance with the described embodiment shown in the figures, the module 10 comprises a flexible printed circuit board (PCB) 9, a plurality of rows of ultra- thin LEDs in the form of a LED subassembly 8 mounted on the PCB 9, and a plurality of optical layers coupled to the LED subassembly 8, all of which are contained in a housing 3.

The optical layers comprise a light guide plate layer (LGP) 5, a reflector film layer 6 and a diffuser layer 4. In one embodiment of the invention, the optical layers may further comprise a brightness enhancement film (BEF) layer. Each optical layer comprises at least one low friction, thin film.

In one embodiment of the present invention the light guide plate layer 5 is coupled to the LED subassembly 8 by an adhesive means. This adhesive means comprises a light reflective adhesive film which is attached between the top and bottom surfaces of the LED subassembly 8 and the light guide plate layer 5. This adhesive film provides for a connection between the LED subassembly 8 and the optical layers, while at the same time enabling the transmission of light from the LED subassembly 8 through to the optical layers.

In the described embodiment of the invention, the LGP 5 is a thin plastic plate that contains thousands of features in the form of tiny bumps and ridges formed by an injection molding or laser etching process or silkscreen printing. These features allow for light extraction from the plastic plate, and thus prevent the occurrence of total internal reflection. Thus, total internal refraction occurs within the LGP 5 until the light hits one of these features. The LGP 5 is also adapted to maximise the uniformity of the light extracted by the features. Thus, the LGP 5 is designed so that there are fewer features near the LEDs, and an increasing number of features as the distance away from the LEDs increases. In one embodiment of the invention, the LGP 5 is fabricated from acrylic (poly methyl methacrylate). In another embodiment of the invention the LGP 5 is fabricated from high density polyethylene (HDPE). These materials provide a LGP of high optical performance.

Each of the reflector film layer, the diffuser layer and the BEF layer may be fabricated from any suitable plastic, such as for example acrylic, polyester and polyethylene terephthalate (PET).

In one embodiment of the invention, the reflector film layer 6 comprises a specular reflector film (SR) layer which is adapted to reflect any light received from the LGP 5 upwards towards the emission plane. In an alternative embodiment, the reflector film layer 6 comprises a diffuse reflector film layer. The diffuser 4 increases the uniformity of the light emitting surface (LES), and also influences the photometry of the light source by effecting the amount of light emitted off- angle from the normal of the LES. However, it should be noted in this regard that the BEF has a greater effect on this photometry, while the diffuser 4 is primarily for uniformity. In the embodiment of the invention where the optical layers further comprise a BEF, the BEF contains prism shaped features that refract light moving at a high angle to the normal of the module to bring it closer to the normal. This improves the photometric properties of the module, by increasing the directivity of the light while maintaining adequate diffusion. In the described embodiment of the invention, the BEF comprises a single optical film. Flowever, it will be appreciated that in alternative embodiments of the invention, a plurality of BEF films could be used in the module 10, in order to enable the module 10 to emit a plurality of light beams of different angles.

In one embodiment of the invention, the module 10 also includes a protective outer optical transparent layer or cover film 1 for preventing scratches and damage to the module 10. An internal rim secures the optical transparent protective layer in place.

A pressure sensitive adhesive (PSA) 2 attaches the cover film 1 to the housing 3. In the described embodiment of the invention, the PSA 2 takes the form of a double-sided adhesive tape.

The multiple LEDs forming the LED subassembly 8 provide a high total light output for the module. These LEDs may be either top or side emitting LEDs. The LEDs are soldered onto the flexible PCB 9 via surface mounted technology (SMT) and are connected to allow for a single point for the power supply to enter the module. In one embodiment of the invention, two rows of side emitting LEDs are provided, one row on two opposing sides of the PCB 9. This arrangement provides for very efficient light extraction. The PCB 9 connects the LED subassembly 8 to the external power supply and is designed to transform the supplied current and voltage to the optimal power supply for each individual LED. The external power supply may be a standard LED constant current driver. The driving voltage and current are dependent on the number and type of LEDs, as well as the target light output from the module. In one embodiment of the invention, the LED subassembly 8 comprises ultra-thin warm white (2700K), neutral white (3000K) or cool white (4000K) LED chips. The housing 3 is a plastic. In one embodiment of the invention, the housing has a Young’s Modulus within the range of 0.1 GPa to 2.0 GPa, and preferably between 0.2GPa to I .OGPa. The housing may be fabricated from any thermoplastic such as for example polycarbonate, HDPE or polypropylene (PP). The housing 3 may also be coloured white, in order to maximise internal reflectivity.

The module of the present invention is designed so that there is no raised bezel on the light emitting surface. This is achieved through the provision of an internal rim or bezel 13 on the module 10. In the embodiment of the invention shown in Figure 8, this rim 13 extends around all four sides of the housing 3 in order to secure the cover film 1 in place. This rim acts as both a light shield to define the active area, as well as a surface to attach to the cover film 1 . The cover film 1 can then be attached to the housing through the PSA 2. In the described embodiment of the invention, the housing edges are flush with the cover film 1 . This prevents peeling of the cover film from the module during handling and over lifetime. In one embodiment of the invention, the module has a thickness of less than 4.0 mm. In an exemplary embodiment of the invention, the module has a thickness of 3.2mm.

In one embodiment of the invention, the rim or bezel 13 is fabricated by means of an injection molding process as part of the housing 3. In an alternative embodiment of the invention, the bezel 13 is fabricated by means of a silkscreen printing process on one of the plurality of optical layers. This process involves the silkscreen printing of an opaque white ink on the underside of the top optical layer.

There are a number of advantages associated with fabricating the bezel 13 by means of this silkscreen printing technique. Firstly, it prevents the LED subassembly 8 and other internal components from being visible, as is also the case for when the bezel is fabricated by means of an injection molding process. It also provides a sharp edge for the light emission and reflects the light internally in order to maximise the total light output from the module 10. Furthermore, by using the silkscreen printing technique, it enables the module 10 to be assembled from the top down, which can be advantageous for ease of production. It should be understood however that the housing 3 still acts as the mounting support for all the individual components of the module 10, including the LED subassembly 8, the PCB 9 and the plurality of optical layers. The silkscreen printed optical layer is attached to the housing 3 via an adhesive layer.

It will be appreciated that a number of different methods could be employed to assemble the optical layers into the housing 3 in order to form the module 10. For example, the diffuser layer 4, the light guide plate layer 5 and the reflector film layer 6 could be individually placed on top of each other in the housing 3 with no connection between them, thus forming a plurality of“free floating” optical layers. The housing 3 could then be sealed to constrain these components. The seal may be provided by any suitable means, such as for example through the use of adhesive tapes, glues or screws.

In one embodiment of the invention, the light guide plate layer 5, reflector film layer 6, and diffuser layer 4 are first mounted together to form a light guide plate subassembly 16, with the light guide plate subassembly 16 then being mounted to the housing 3. A cross section of the light guide plate subassembly 16 is shown in Figure 9, while an exploded view of the components of the module prior to final assembly is shown in Figure 10.

The light guide plate subassembly 16 is fabricated by attaching the diffuser layer 4 to one side of the light guide plate layer 5 and attaching the reflector film layer

6 to the other side of the light guide plate layer 5.The light guide plate subassembly 16 is then mounted to the housing 3 such that the diffuser layer 4 is located above the light guide plate layer 5 and adjacent to the BEF layer, in the embodiment where the module includes a BEF layer, or adjacent to the cover layer 1 in the embodiment where the module does not include a BEF layer, while the reflector film layer 6 is located below the light guide plate layer 5 and adjacent to a back film 7. In one embodiment of the invention, the diffuser layer 4 and the reflector film layer 6 are attached to the light guide plate layer 5 by means of a double-sided adhesive tape (known as a ring tape) which is provided around the perimeter of the light guide plate layer 5. Thus, a first double sided adhesive tape 17 is provided around the top perimeter of the light guide plate layer 5 to attach the diffuser layer 4 to the light guide plate layer 5, while a second double sided adhesive tape 18 is provided around the bottom perimeter of the light guide plate layer 5 to attach the reflector film layer 6 to the light guide plate layer 5. However, it will be appreciated that any other suitable attachment means could be used to directly attach both the diffuser layer 4 and the reflector film layer 6 to the light guide plate layer 5 in order to form the light guide plate assembly 16. For example, in an alternative embodiment, a layer of optically clear adhesive (OCA) could be used to form the attachment between the light guide plate layer 5 and each of the diffuser layer 4 and the reflector film layer 6.

In one embodiment of the invention, the light guide plate subassembly 16 is mounted to the housing 3 by means of a snap-fit connection between the light guide plate subassembly 16 and the housing 3. This cantilever snap fit feature 19 can be seen in Figure 9 protruding from the light guide plate subassembly 16.

Figure 1 1 shows an exploded view of the light guide plate subassembly 16 positioned above the housing 3 with the snap-fit features 19 of the light guide plate subassembly 16 aligned for mating with corresponding notches 20 on the housing 3. The snap-fit connection thus comprises a first pair of spaced apart cantilever snap fit features 19 located on one edge of the light guide plate subassembly 16 adapted to mate with a complimentary first pair of spaced apart notches 20 located on the corresponding side of the housing 3, and a second pair of spaced apart cantilever snap fit features 19 located on a second edge opposite the first edge of the light guide plate subassembly 16 adapted to mate with a complimentary second pair of spaced apart notches 20 located on the corresponding side of the housing 3.

It should be noted that the snap-fit features do not optically impact the performance of the module, as they are located on the two edges of the light guide plate subassembly 16 which are perpendicular to the sides 14,15 of the module on which the rows of side emitting LEDs of the LED subassembly 8 are located. Furthermore, the notches are completely internal in the housing, so they are not visible from the final assembled module.

Figure 12 shows a detailed perspective view of a notch 20 in the housing 3 which is adapted to receive a cantilever snap fit feature 19 of the light guide plate subassembly 16, while Figure 13 shows a detailed top view of one cantilever snap-fit feature 19 of the light guide plate subassembly 16 mated with its corresponding notch 20 on the housing 3.

There are a number of advantages of using a light guide plate subassembly in the manufacture of the module of the invention. Firstly, the light guide plate subassembly can now be manufactured separately to the final assembly production line using a process that is reliable and repeatable. This enables a high manufacturing yield to be achieved, as a result of increased control in the alignment of the optical films due to the light guide plate being directly attached to the diffuser layer and the reflector film layer. It also reduces the risk of film warping and unwanted bending between the optical layers. This arrangement also reduces contamination in the form of dust between the diffuser layer 4, the reflector film layer 6 and the light guide plate layer 5, as the light guide plate subassembly is created separately in a controlled environment. This approach also provides for a simplified final assembly of the module, as the light guide plate subassembly comprising the diffuser layer 4, the reflector film layer 6 and the light guide plate layer 5 can now be inserted into the housing 3 as a single process step, with the final assembly being better controlled, due to the fact that the diffuser layer 4, the reflector film layer 6 and the light guide plate layer 5 are no longer free floating, and thus do not require positioning and placement accuracy.

The use of a snap-fit connection between the light guide plate subassembly 16 and the housing 3 also provides a number of additional benefits when compared to a module design where the optical layers are free floating. Such a connection increases the overall robustness, controllability and reliability of the assembly of the module, as well as the alignment between layers. It also provides for a simpler assembly of the module, as the light guide plate subassembly 16 comprising the optical layers is adapted to mate into the correct location in the housing 3.

The snap-fit connection provides for a robust, permanent mechanical fixation, and prevents detachment over the life of the module, without the requirement to use adhesive films, glues or screws.

In use, light emitted by the LED subassembly 8 directly enters into the LGP 5. The LGP 5 reflects and refracts the light in the perpendicular direction to the incoming light source in the form of the LED subassembly 8, and allows the light to escape from the light guide plate 5. Approximately half of the light initially leaves the LGP 5 in a downwards direction, at which point the light is reflected upwards again by the reflector film layer 6. Light that leaves the LGP 5 in the upwards direction, either as a result of one of the features on the LGP 5, or from being reflected by the reflector film layer 6, then enters the diffuser 4. Once the light is diffused through the diffuser 4, it is emitted out of the module through the cover film 1 as a surface of light (via the BEF layer in the embodiment where the module includes a BEF layer).

The module 10 of the present invention may be mounted either at the back or front. In one embodiment of the invention, the module 10 is mounted at the back via an attachment means comprising a self-adhesive film (which may be thermally conductive) onto the thermally conductive back film 7. This back film 7 therefore allows for both effective thermal management and for use as a mounting surface. This enables the attachment of the module to be permanent or semi-permanent. In addition, the attachment of the module does not require any additional tools and does not affect the external finish of the module.

In an alternative embodiment, the module is mounted at the back via a stretch release tape (not shown). This material allows greater flexibility for detaching the module. For front mounting, an optically clear adhesive film (OCA) may be used. It comprises a double sided adhesive film that allows maximum light transfer for when the module is mounted onto a transparent material, such as glass or plastic. This OCA layer covers the entire front face, over the optically transparent cover film 1 .

A recessed groove is provided on the module 10 for the wiring of the module which has dimensions less than the thickness of the module, with the groove ensuring the wiring does not protrude above the back film 7. In one embodiment of the invention, the groove 1 1 is provided at a 45 degree angle to the sides of the housing 3, and has filleted openings to the housing sides, as shown in Figure 4. This design facilitates a number of different configurations options for the wiring, so as to minimize the visual impact of the wiring depending on the desired use of the module, such as for example in lighting fixtures, furniture, walls or ceilings.

Figures 5 to 7 show a number of alternative wiring configurations for the module. In Figure 5, the wiring 12 is arranged in the groove 1 1 so that it emerges diagonally from a corner of the housing 3, such as at a nominal 45 degree angle.

In Figure 6, the wiring 12 is arranged in the groove 1 1 so that it emerges coincident to an edge of the housing 3. This is made possible by the filleted openings in the groove 1 1 , such that the wiring can be bent around these openings to go from a diagonal to a coincident direction to an edge of the housing. In Figure 7, the wiring 12 is arranged in the groove 1 1 so that it emerges set back a few millimetres from a corner of the housing 3 and perpendicular to the housing 3. This configuration enables the wiring to be passed through an aperture in a surface to which the module is to be attached, and the wiring will then be hidden behind the module once the module is attached to the surface. As a result, there is no visible wiring to be seen on the module, so creating an appealing aesthetic finish.

Figure 8 shows a view of one exemplary configuration of wiring within the module 10 (shown with the thermally conductive back film removed). It can be seen from this figure that the path of the wiring 12 is such that it follows around the sides of the housing 3 and passes through the internal rim 13. In one embodiment, the wiring 12 is anchored in place in this position by an adhesive means. This configuration provides a high level of strain relief to the wiring 12 and prevents damage to the module 10 if the wiring 12 is tugged. This figure also illustrates the embodiment where the LED subassembly 8 comprises two rows of side emitting LEDs, wherein one row of side emitting LEDs is located on one side 14 of the module 10 and the other row of side emitting LEDs is located on the opposite side 15 of the module 10.

One aspect of providing these different wiring configurations is to provide robust strain relief, preventing stress and fracture where the external wiring connects to the PCB 9 of the module. This is achieved using a high strength resin or glue which anchors the base of the wiring within the groove 1 1 before it emerges from the housing 3.

It will further be appreciated that in the embodiment of Figure 8 the recessed groove 1 1 provided on the module 10 for the wiring 12 is provided parallel to the sides of the housing 3, rather than at a 45 degree angle to the sides of the housing, as shown in Figure 4.

The performance and lifetime of LEDs is severely impacted by overheating. Accordingly, a path for thermal transfer away from the LED subassembly is always necessary. Thus, the use of a thermally conductive back film on the back of the housing and further thermal films between the LEDs and the back film 7, and the design of using multiple low power LEDs improves the thermal performance of the module. In one embodiment of the module, graphite is used to further improve thermal spreading and increase thermal conductivity between the LEDs and the back film. The graphite is positioned as a layer between the LED subassembly 8 and the thermally conductive back film 7.

The present invention provides numerous advantages when compared to existing technology for producing a surface of white light. Firstly, due to its modular design, the module is suitable for complex and aesthetic luminaire design and mounting in a way that cannot be achieved with existing LED lighting technologies.

Furthermore, the ultra-thin design reduces the total required size for the luminaire. As a result, the invention can be used in small spaces, such as under a shelf or in a drawer. Through the use of multiple rows of LEDs for small area illumination, the light output relative to the dimensions of the module is also very high and does not cause glare associated with point light sources. Furthermore, the LEDs are thermally managed in order to maintain their performance.

The fabrication costs of the module of the invention are also lower when compared to existing OLED lighting modules of similar form factor, and of inferior efficacy and lifetime performance.

The module of the present invention does not require secondary optical controls to provide a comfortable, low glare light source. The module also has the advantage that it can be powered through the use of existing LED driver technology, and integrated with current LED lighting ecosystems.

As a result of the flush bezel design, the module may be directly mounted onto transparent surfaces. It also enhances the aesthetic appearance of the module. In addition, the fact that the module may be mounted using adhesive films results in simplified installation for the luminaire manufacturer.

It will further be appreciated that the present invention is not limited to use with a luminaire and can be used as a standalone module too. It therefore has applications in any area where a small uniform surface of light is required. Such areas include use in decorative applications in furniture, for illuminated signage, and in medical and industrial equipment. The present invention also has applications where space is limited, such as in automotive or aerospace interiors.