WO2018029285A1

WO2018029285A1 - A planar led light source module

Info

Publication number: WO2018029285A1
Application number: PCT/EP2017/070256
Authority: WO
Inventors: Matthew HANBURY
Original assignee: Lightly Technologies Limited
Priority date: 2016-08-10
Filing date: 2017-08-09
Publication date: 2018-02-15
Also published as: GB2552807B; GB2552807A

Abstract

A light emitting diode, LED, light source module for a luminaire. The LED light source module comprises a 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. The optical layers are adapted to be slidable with respect to

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 flexible LED light source module for producing a 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

Accordingly 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 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 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 backplane film attachable to 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: 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 3.0 mm.

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.

Accordingly 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 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. 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 a 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; and

Figure 8 shows a view of one exemplary configuration of the wiring within the light source module of Figure 1 .

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 flexible 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 flexible housing 3.

The optical layers comprise a light guide plate layer 5, a reflector film layer 6, a diffuser layer 4, and a brightness enhancement film (BEF) layer 1 . Each optical layer comprises at least one low friction, ultra- thin film such that the optical layers can slide over each other when bent. As a result, the module provides flexibility and can be bendable about one or both of its x and y axes. In one embodiment of the present invention the light guide plate layer 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 flexible 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. 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 high density polyethylene (HDPE) having a Young's modulus of 0.8GPa. This material provides a LGP of high flexibility and optical performance. However, it will be appreciated that any other suitable flexible material could be used.

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 1 has a greater effect on this photometry, while the diffuser 4 is primarily for uniformity.

The BEF 1 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 photometic properties of the module, by increasing the directivity of the light while maintaining adequate diffusion. In the described embodiment of the invention, the BEF 1 comprises a single optical film. However, 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.

A pressure sensitive adhesive (PSA) 2 attaches the BEF 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 dependant on the number and type of LEDs, aswell as the target light output from the module. In one embodiment of the invention, the LED subassembly 8 comprises ultra-thin warm white (3000K) or neutral white (4000K) LED chips. The housing 3 is a flexible plastic. In one embodiment of the invention, the housing has a Young Modulus within the range of 0.1 GPa to 2.0 GPa, and preferably between 0.2GPa to 1 .OGPa. The housing may be fabricated from any stable, flexible material, such as for example HDPE or polypropylene (PP). In the described embodiment of the invention, the flexibility is optimized through the use of slots provided in the PCB 9. 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 BEF 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 BEF 1 . The BEF 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 BEF 1 . This prevents peeling of the BEF from the module during handling and over a lifetime. In one embodiment of the invention, the module has a thickness of less than 3.0 mm.

In one embodiment of the invention, the rim or bezel 13 is fabricated by means of an injection molding process on 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 a 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.

In one embodiment of the invention, the module 10 further includes a protective outer optical layer mounted to the BEF 1 layer for preventing scratches and damage to the module 10 (not shown). This protective outer optical layer comprises an optically transparent layer in the form of an optically clear film. In this embodiment, it will be appreciated that the rim secures the outer optical layer in place.

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 BEF 1 as a surface of light.

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 in the form of a backplane 7 comprising a thermally conductive self-adhesive plastic film. This back film therefore allows for both effective thermal management and reduced total thickness. 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 effect 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 great 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 BEF layer 1 . Alternatively, in the embodiment of the invention where a protective outer optical layer is mounted to the BEF layer 1 , the OCA layer is mounted instead to the outer optical layer.

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 backplane 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 backplane removed). It can be seen from this figure that the path of the wiring 1 2 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 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 thermal tapes on the back of the housing 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 backplane. The graphite is positioned as a layer between the LED subassembly 8 and the adhesive backplane 7.

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

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 bezel-less 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 mechanically 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 as a microscope backlight, 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.

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 housing;

2. The LED light source module of Claim 1 or Claim 2, wherein the optical layers comprise:

a light guide plate layer;

a reflector film layer;

a diffuser layer; and

a brightness enhancement film, BEF layer.

3. The LED light source mode of Claim 2, wherein the light guide plate layer is fabricated from one of: high density polyethylene and each of the reflector film layer, the diffuser layer and BEF layer are fabricated from one of: acrylic, polyester and polyethylene terephthalate (PET).

4. The LED light source module of Claim 2 or Claim 3, wherein 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.

5. The LED light source module of Claim 4, wherein the edges of the housing are flush with the BEF for direct mounting of the module onto a surface.

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

7. The LED light source module of Claim 6, wherein the attachment means comprises a thermal conductive adhesive backplane film attachable to the housing.

8. The LED light source module of Claim 6, wherein the attachment means comprises a stretch release tape attachable to the housing.

9. The LED light source module of Claim 6, wherein the attachment means comprises an optically clear adhesive film attachable to the BEF layer.

10. The LED light source module of any of the preceding claims, wherein the housing comprises a flexible plastic.

11. The LED light source module of any of the preceding claims, wherein the housing has a Young Modulus in the range of 0.1 to 2.0 Gpa, and preferably between 0.2GPa to LOGPa.

12. The LED light source module of Claim 1 1 , wherein the housing is fabricated from one of: high density polyethylene or polypropylene.

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

14. The LED light source module of Claim 13, wherein the flexible PCB comprises a PCB provided with plurality of slots to improve flexibility.

15. 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.

16. The LED light source module of any of the preceding claims, wherein the thickness of the module is less than 3.0 mm.

17. The LED light source module of any of the preceding claims, wherein 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.

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

19. The LED light source module of Claim 18, 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.

20. The LED light source module of Claim 2, wherein the light guide plate layer is coupled to the LEDs by an adhesive means.

21 . The LED light source module of Claim 20, wherein the adhesive means comprises a light reflective adhesive film attached between the LED

subassembly and the light guide plate layer.

22. The LED light source module of Claim 4, 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.

23. The LED light source module of Claim 2, further comprising an optically transparent protective layer mounted to the BEF layer.

24. The LED light source module of Claim 4, wherein the internal rim is fabricated by means of an injection molding process on the housing.

25. The LED light source module of Claim 4, wherein the internal rim is fabricated by means of a silkscreen printing process on one of the plurality of optical layers.