WO2008114200A1

WO2008114200A1 - Flexible light source

Info

Publication number: WO2008114200A1
Application number: PCT/IB2008/050993
Authority: WO
Inventors: Leendert Van Der Tempel; Rabin Bhattacharya; Chantal Sweegers; Jacob Klerk; Peter H. F. Deurenberg; Stefan M. Verbrugh; Willem L. Ijzerman
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-03-22
Filing date: 2008-03-17
Publication date: 2008-09-25

Abstract

The present invention relates to a flexible light source (100), adapted to be bent in at least one direction so as to form a line of curvature (Lc), comprising a translucent substrate (104), at least one light emitting diode (102) arranged to emit light into said substrate, and at least one light guide (103) arranged in the path of light between said at least one light emitting diode and said substrate. By placing the LEDs on the rear side of the translucent substrate, heat generated during operation of the LEDs may be transferred to the surrounding atmosphere, thus reducing the risk of overheating. In this way, the LEDs may be operated at temperatures which promote their efficient and long-lasting performance.

Description

FLEXIBLE LIGHT SOURCE

FIELD OF THE INVENTION

The present invention relates to a flexible light source and to a system comprising a light source and a supporting structure, wherein said light source is arranged to be fixed to said supporting structure.

BACKGROUND OF THE INVENTION

The requirements on lighting applications from architects, engineers and interior designers continually present new challenges for the lighting industry. Efficient, robust, cost-effective, versatile and aesthetic are some examples of the desired properties of light sources today, especially for professional environments. In particular, there is a demand for light sources which are easily mountable on various types of non-planar and/or irregular surfaces, such as a curved wall or a curved ceiling structure.

US 5,162,696 discloses a flexible panel comprising a plurality of light emitting diodes (LEDs). The panel has the ability to conform to curved surfaces and is self-supporting by means of suction cup devices provided on the back side of the panel. Moreover, the panel comprises a light transmissive, heat resistant PVC envelope enclosing the LEDs.

In operation, LEDs generate energy, both in terms of heat and in terms of light intensity. Especially when operated for extended time periods, the generated heat may seriously impair the performance of the LED with respect to brightness, efficiency and lumen output, and may also reduce the life span of the LED.

The panel disclosed in US 5,162,696 is primarily intended for use as a moving message information display. Considering the larger amount of heat generated from a plurality of continuously operated LEDs for general lighting, compared to that of a device in which a lesser amount of LEDs are momentarily operated, such as in an information display, it is clear that the panel of US 5,162,696 is not suitable for general lighting purposes, as the LEDs are enclosed within a heat-resistant PVC envelope having no cooling equipment.

Thus, there is a need in the art for a light source which is flexible enough to be mounted on a curved structure and which is suitable for professional general lighting applications. SUMMARY OF THE INVENTION

One object of the present invention is to at least partly overcome the above- mentioned problems associated with prior art and to provide a light source which may be mounted on curved or irregular surfaces.

Another object of the present invention is provide a light source which may be operated at temperatures which promote its efficient and long-lasting performance.

Another object of the present invention is provide a light source which may be easily and cost-effectively manufactured and transported. Another object of the present invention is to provide a light source which is easy to install.

These and other objects are achieved by a light source according to the appended claims.

Thus, in one aspect, the present invention provides a flexible light source, adapted to be bent in at least one direction so as to form a line of curvature, comprising a translucent substrate, at least one light emitting diode arranged to emit light into said substrate, and at least one light guide arranged in the path of light between said at least one light emitting diode and said substrate.

As the light source is flexible in at least one direction, it is easily rolled to a roll for convenient transportation. Further, convenient transportation of rolls of large units allows cost-effective manufacturing of large units, which subsequently may be cut to measure on the installation site.

Also, to allow bending, the light source must be rather thin, which means that it requires rather small front side and back side spaces when mounted. By placing the LEDs on the back side of the translucent substrate, the problem of overheating is reduced as heat generated during operation of the LEDs may be transferred to the surrounding atmosphere.

Furthermore, the substrate may be divided along the line of curvature into a plurality of regions, each region comprising at least one light guide, adjacent regions being mutually bendable. The division of the substrate into regions facilitates bending while allowing for many different substrate designs.

The translucent substrate of the light source of the present invention may be made of a flexible material. A flexible substrate material allows bending in any direction, thus providing an extremely versatile light source, which can be mounted in any shape. The light source may comprise adhesive material provided on the rear side of the translucent substrate, enabling quick and easy installation of the light source. The use of an adhesive material for attaching the light source to a surface is particularly advantageous in combination with a flexible substrate material, thus enabling mounting of the light source on surfaces or structures of virtually any shape.

Furthermore, the light source may comprise a heat spreader arranged in rear of the light guide. In order to operate LEDs at temperatures which promote their efficient and long-lasting performance, it is preferred that heat energy is transported away from the LED. This is at least partly achieved using a heat spreader which serves to distribute heat away from the LED.

In many lighting applications, it is desirable that the light from a light source is rather homogeneously distributed. In embodiments of the present invention, the light source comprises a light guide plate having at least two light receiving faces, one light output face and a plurality of extracting structures. Light which is received into the light guide via one of the at least two light receiving faces is mixed with light received via another light receiving face before exiting the light guide via the light output face. Thus, light from a plurality of LEDs is received into the light guide via a plurality of light receiving faces and is distributed therein before exiting. Hence, the light source of these embodiments provides well distributed light from a plurality of point light sources. The translucent substrate may comprise a prismatic surface. A prismatic surface serves to redirect the incident light, and by using such a surface, the light source can thus be adapted to emit the light in a desired direction.

In embodiments of the present invention, the light source comprises at least one rigid rod element arranged perpendicular to the line of curvature, at least one rod element being arranged between two adjacent substrate regions.

For the handling of the light source when rolled, it may be advantageous that the light source maintains some degree of rigidity. The use of rod elements provides one- dimensional rigidity while still allowing bending in said bending direction, which facilitates the rolling procedure and the transportation of the roll, maintaining the possibility of mounting the light source on a curved structure. Additionally, as a result of the rod elements the light source may more easily be mounted in a flat manner.

Further, the light source may be divided into separate sections, two adjacent sections being joined together by means of one of said rod elements. Dividing the substrate into separate sections and joining them using rod elements allows the use of a relatively rigid substrate material, while still achieving flexibility by means of the connection, e.g. a hinge, between the sections and the rod elements. The possibility of using a relatively rigid substrate is advantageous, as this renders the choice of substrate material less restricted.

In embodiments of the present invention, the light source comprises at least one rod element extending outside the lateral edge of the translucent substrate. By having one or several rod elements extending outside the lateral edge of the substrate, the rod elements may be utilized for attaching the light source to a supporting structure, without the addition of separate means for attachment. In this manner, the installation and the manufacturing procedures may be simplified. In another aspect, the invention relates to a system comprising a light source and a supporting structure, wherein the light source is arranged to be fixed to the supporting structure. The use of a predefined supporting structure facilitates installation of the light source, thus saving time and cost of this process.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic view of a light source of the present invention.

Figure 2a is a schematic view of another light source of the present invention.

Figure 2b is a schematic cross-sectional view of a light source of the present invention along the line of curvature (Lc). Figure 3 is a schematic view of a light source of the present invention illustrating the line of curvature (Lc) formed formed upon bending of the light source, the substrate being divided into a plurality of regions.

Figure 4 is a schematic cross-sectional view of one example of a light guide used in a light source of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a light source, adapted to be bent in at least one direction so as to form a line of curvature (Lc), comprising a translucent substrate, at least one light emitting diode and optionally at least one light guide. The term "translucent", in the context of the optical properties of a material, refers to the the material being transmissive to light. "Translucent material" is thus to be interpreted as encompassing both transparent, i.e. optically clear, and diffusive transmissive material. Herein, the term "light guide" refers to an optical element having at least one light receiving face through which light is received into the light guide, and a light output face through which light is intended to exit from the light guide. Further, at least part of the light received into the light guide is subject to total internal reflection. Moreover, a light guide as defined herein comprises at least one light extracting structure such that at least part of the light incident on such a light extracting structure is extracted from the light guide.

Herein, "front side" refers to the side of a component of the light source, or of the light source as a whole, intended as the viewing side, i.e. the side of the component or of the light source which is intended to face the viewer of the light. Consequently, "back side" or "rear side" refers to the side of a component of the light source, or of the light source as a whole, intended to be facing away from the viewer of the light.

A first embodiment of a light source according to the present invention is shown in Fig. 1. The light source 100 is adapted to be bent so as to form a line of curvature Lc. The light source 100 comprises a transparent substrate 101, a plurality of LEDs 102 provided on the back side of the substrate 101 and a plurality of light guides 103. The LEDs 102 are arranged to emit light into the substrate 101.

The transparent substrate 101 may consist of a transparent material, e.g. plastic, ceramic, or glass. Suitable materials are known to those skilled in the art. The substrate material may itself be flexible enough to be bent so as to form a line of curvature Lc. A flexible substrate material allows bending in any direction, thus allowing the light source to be mounted in any shape. Typically, the transparent substrate 101 is a PVC sheet. The transparent substrate 101 has a typical thickness of from 0.15 to 0.2 mm.

Further, the transparent substrate 101 may have a small percentage shrinkage upon heating at 38-50 °C. This heating may be realised by switching on the LEDs 102. The transparent substrate 101 may comprise one single layer of transparent material, or multiple layers of transparent material.

The substrate usually being very thin, it is easily bent in at least one direction, allowing production of the light source to a roll, thus greatly facilitating manufacturing and transportation of large units. As an example, the radius of curvature may be as low as 10 mm. Also, being thin, the light source requires rather small front side and back side spaces when mounted.

Those areas of the transparent substrate 101 which are illuminated by the LEDs 102 may comprise a prismatic surface. A prismatic surface may for example be present in at least one substrate layer. A prismatic surface serves to redirect the incident light and may be used to emit the light exiting from the translucent substrate in a desired direction. Using a prismatic surface, the light source may be thus be adapted to fit many different constructional environments.

The light source may also be adapted to emit light in a plurality of specified directions. Preferably, the prism apices of the prismatic surface are directed towards the rear side of the light source, thus facing the LED.

The translucent substrate may have a diffusely reflecting surface. Furthermore, the substrate may be at least partly printed, e.g. for decoration purposes.

Further, the light source 100 comprises light guides 103 arranged in the path of light between the LEDs 102 and the transparent substrate 101. Each light guide 103 may for example have the shape of a plate. With reference to Fig. 1 and 4, the light guide 103, 400 is provided such that light from the LEDs 102, 404 enters the light guide 103, 400 via at least one light receiving face 401 and exits the light guide 103, 400 via the light output face 402 and subsequently enters the transparent substrate 101. Preferably each of the light guides 400 is a plate having at least two light receiving faces 401 and 401 ', one light output face 402 and a plurality of extracting structures 403, wherein light received into said light guide 400 via one of said at least two light receiving faces 401, 401 ' is mixed with light received via another one of said light receiving faces 401, 401 ' before exiting the light guide 400 via the light output face 402. Fig. 4 also shows a LED 404. Each of the light guides may comprise collimating structures such that the light exiting the light guide has a lower angular spread than the light entering the light guide. When this is the case, the light guides serve to collimate and redirect the light exiting from the LEDs before entering the translucent substrate. Alternatively, a collimating structure may be provided outside the light guide, collimating the light from the LED before it enters the light guide. A collimating structure improves the capacity of the light source of emitting the light in a specified direction and also improve the efficacy of the light source by reducing the angular distribution of the light.

Furthermore, in many lighting applications, it is desirable that the light from a light source is rather homogeneously distributed. In this embodiment, light from a plurality of LEDs is received into each light guide via a plurality of light receiving faces and is distributed within the light guide before exiting via the output face. Hence, each light guide distributes light from a LED to a larger area so that a plurality of LEDs, although typically being point sources of light, can be used in a light source of the invention to homogeneously illuminate a large surface area. For constructional purposes it is preferred that the flexible light source may have a variety of substrate designs and that the substrate may be made of different materials. In this embodiment of the invention, the translucent substrate 101 is divided along the line of curvature Lc into a plurality of regions 104, 104', each region 104, 104' comprising at least one light guide 103. The division of the substrate into regions facilitates bending while allowing many different substrate designs.

Further, the light source 100 is provided with appropriate power supply equipment. In Fig. 1, main electrically conductive wires 106 and low voltage secondary wires

107 are provided on the back side of the substrate 101. The main wires 106 are running in a direction along the line of curvature Lc. The wires 106 may for example be centrally located on the substrate 101, or located at any of the lateral edges 105, 105' of the substrate 101. Location of the main wires 106 to the lateral edge 105 or 105' may assist in preventing sagging of the substrate 101. The low voltage wires 107 may be arranged running in a direction perpendicular to the line of curvature Lc. The wires 106 and/or wires 107 may be adapted to accommodate for a possible shrinkage of the substrate due to heating, e.g. by having a zig-zag or corrugated topology, or by being arranged on elastic cores. For example, the wires 106 and 107 may be wound around elastic cores. The wires may for example be made from metal yarn, such as copper yarn.

Moreover, the light source 100 of this embodiment comprises at least one power electronics module 108 having a high frequency switch mode, e.g. by means of a flyback or resonant converter, further comprising the appropriate power factor correction means and filters, and optionally insulation to meet legal safety requirements. The module

108 may be mounted on a flexfoil or other PCB base material.

Optionally the light source 100 may comprise at least one heat spreader 109 for distribution of the heat generated by the LED 102. The heat spreader 109 may be comprised of a heat conductive material, such as metal. During operation, LEDs generate heat which, in particular during long-term operation, causes a reduction of the efficiency and the life-span of the device. By using a heat spreader to improve heat transport from the LED, the LED can be operated at temperatures which promote its efficient and long-lasting performance.

In embodiments of the present invention, the light guide, having a relatively large surface area, is used as a heat sink, being cooled by the surrounding atmosphere. In order to transport heat from the heat spreader to the light guide, good thermal transport properties there between are desired. However, to obtain good light propagation, it is preferred that total internal reflection can occur in the surfaces of the light guide, including the back surface. The distance between the light guide and the heat spreader must be substantially above the wavelength of the light in order to allow total internal reflection within the heat spreader, and is typically about 2 μm or more. However, to maintain good heat transfer between the light guide and the heat spreader, the distance should typically not exceed about 200 μm. For increasing the heat transfer between the light guide plate and the heat spreader, the distance should be as small as possible, while being relatively simple to obtain. For example, the heat spreader 109 may be arranged at a distance of from 5 to 15 μm from the light guide 103, e.g. using spacers. Light sources of the invention may be used for general lighting purposes.

Particularly, light sources of the invention may be mounted on a wall, or mounted as stretch ceilings having integrated lighting. Hence the light source may be adapted to suit various constructional requirements, e.g. to comprise perforations for sprinklers or air conditioning. In order to be easily mountable on a supporting sur-face, a light source of present the invention may be provided with an adhesive material on its rear side. The use of an adhesive material allows the light source to be mounted by adhesion only, enabling quick and easy installation. For a flexible light source this is very advantageous, as it enables mounting on surfaces or structures of virtually any shape and does not require any particular fixating arrangements on the surface or structure to be mounted onto. In embodiments of the present invention, the substrate of the light source comprises rod elements. Figure 2a is a schematic view illustrating a light source 200 which is adapted to be bent so as to form a line of curvature Lc. The light source 200 comprises a translucent substrate 201 and a plurality of LEDs 202. Along the line of curvature Lc the substrate 201 is divided into a plurality of regions 203, 203', adjacent regions 203 and 203' being mutually bendable. Further, the light source comprises rod elements 204 which are arranged perpendicular to the line of curvature Lc and in the plane of the substrate 201 between two adjacent substrate regions 203 and 203'. The rod elements 204 provide structural rigidity, while still allowing bending in one direction. This one-dimensional rigidity facilitates the rolling procedure and the transportation of the roll, while maintaining the possibility of mounting the light source on a curved structure. Moreover, due to the presence of the rod elements, the light source may more easily be mounted in a flat manner.

It is to be noted that when the substrate of the light source comprises rod elements, it is not necessary, although possible, for the light source to comprise a light guide. Hence, the present invention also relates to a flexible light source 200, adapted to be bent in at least one direction so as to form a line of curvature Lc, comprising a translucent substrate 201 having a front side and a rear side, and at least one light emitting diode 202 arranged to emit light into said substrate 201, wherein said substrate 201 is divided along said line of curvature Lc into a plurality of regions 203, 203', adjacent regions 203, 203' being mutually bendable, and at least one rod element 204 being arranged perpendicular to the line of curvature Lc between two adjacent of said regions 203, 203'.

Fig. 2b illustrates a light source 200 comprising a translucent substrate 201 which is divided into separate sections 206, 206', 206", two adjacent sections 206 and 206', or 206' and 206", being joined together by means of a rod element 204. Adjacent substrate sections 206 and 206', or 206' and 206", are mutually bendable. Each of the rod elements 204 is flexibly attached to at least one of the two adjacent sections 206, 206', 206", e.g. by hinge means. The use of a flexible joint arranged between two separate, adjacent substrate sections allows the use of a relatively rigid substrate material while still maintaining flexibility in one direction. The possibility of using a relatively rigid substrate is advantageous, as the material to be used for the translucent substrate may be chosen more freely without the requirement of flexible properties, or the substrate sections may be made thicker and hence more difficult to bend.

In embodiments of the present invention, at least one LED 202 is at least partly integrated in the translucent substrate 201. The integration of the LEDs further improves the ro liability of the light source, providing a more even back side.

The invention further relates to a system comprising a light source and a supporting structure. To save time and cost in the process of mounting a light source, it is preferred that the light source is easily mountable. Thus, the system comprises a light source as defined above and a supporting structure, the light source being arranged to be attached to the supporting structure. The use of a predefined supporting structure facilitates installation of the light source. The attachment of the light source to the structure may be performed using any kind of means for attachment. For example, click means may be used for fixing the light source to the suporting structure. By using click means, the fixation of the light source to the supporting structure may be easily and quickly managed. The supporting structure may be mounted on the site of installation before the attachment of the light source.

Claims

CLAIMS:

1. Flexible light source (100, 200), adapted to be bent in at least one direction so as to form a line of curvature (Lc), comprising a translucent substrate (101, 201), at least one light emitting diode (102, 202) arranged to emit light into said substrate (101, 201), and at least one light guide (103) arranged in the path of light between said at least one light emitting diode (102) and said substrate (101).

2. Light source according to claim 1, wherein said substrate (101, 201) along said line of curvature (Lc) is divided into a plurality of regions (104, 104'; 203, 203'), each region comprising at least one light guide (103), adjacent regions (104, 104'; 203, 203') being mutually bendable.

3. Light source according to claim 1 or 2, wherein said substrate (101, 201) is of a flexible material.

4. Light source according to any of the preceding claims, wherein said substrate

(101, 201) comprises a front side and a rear side, an adhesive material being provided on said rear side of said substrate (101, 201).

5. Light source according to any of the preceding claims, comprising a heat spreader (109) arranged in rear of said light guide (103).

6. Light source according to to any of the preceding claims, wherein said light guide (103, 400) is a plate having at least two light receiving faces (401, 401 '), one light output face (402) and a plurality of extracting structures (403), wherein light received into said light guide (400) via one of said at least two light receiving faces (401, 401 ') is mixed with light received via another one of said at least two light receiving faces (401, 401 ') before exiting said light guide (400) via said light output face (402).

7. Light source according to to any of the preceding claims, wherein said translucent substrate (101, 201) has a prismatic surface.

8. Light source according to any of the claims 2 to 7, comprising at least one rigid rod element (204) arranged perpendicular to said line of curvature (Lc), wherein said at least one rod element (204) is arranged between two adjacent of said regions (203, 203').

9. Light source according to claim 8, wherein said substrate is divided into separate sections (206, 206', 206"), two adjacent sections (206, 206', 206") being joined together by means of one of said at least one rod element (204).

10. Light source according to claim 8 or 9, wherein said at least one rod element (204) extends outside the lateral edge (205, 205') of said substrate (201).

11. System comprising a light source according to any one of the claims 8 to 10 and a supporting structure, wherein said light source is arranged to be fixed to said supporting structure.