WO2008102297A1

WO2008102297A1 - Lighting system with improved rigidity

Info

Publication number: WO2008102297A1
Application number: PCT/IB2008/050581
Authority: WO
Inventors: Michel C. J. M. Vissenberg; Peter H. F. Deurenberg
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-02-21
Filing date: 2008-02-18
Publication date: 2008-08-28
Also published as: TW200900766A

Abstract

The present invention relates to a lighting system (100, 200) that comprises a multi-layer stack including a light emitting layer (L1) comprising a plurality of adjacent light emitting elements (102), and a light guiding layer (L2) comprising a plurality of adjacent light guiding elements (110), each adapted to receive light emitted by at least one of the light emitting elements (102) and to alter an optical property of the emitted light, wherein the layers (L1, L2)are positioned in relation to each other such that at least one interface between the plurality of adjacent light emitting elements (102) and at least one interface between the plurality of adjacent light guiding elements (110) do not coincide with each other. The present invention provides for the ability to construct a large area lighting systemusing smaller components based on a modular building concept, wherein the lighting systemexhibit a maintained rigidity in comparison to a prior art large scalelighting system.

Description

Lighting system with improved rigidity

FIELD OF THE INVENTION

The present invention relates to a lighting system, and more specifically to a modular multi- layer stacked lighting system with improved rigidity.

DESCRIPTION OF THE RELATED ART

A recent trend in lighting systems, such as luminaires, is to replace large conventional light sources, such as fluorescent tubes, with a plurality of smaller light sources, in combination providing the required coverage and/or luminance. Owing to previous and ongoing progress and development in the area of light emitting diodes (LEDs), LEDs are presently an advantageous choice of such small light sources, although other alternatives may be found in the future.

A requirement for a lighting system in general, including a LED based one, is that it should be able to provide a well controlled, well defined uniform luminous flux without unintentional spreading and/or obstruction of light. In particular, a lighting system should be able to comply with application specific requirements, for example regarding glare. In many applications, a glare related requirement is that the luminous flux should be uniform and not exhibit any bright spots, not even when the lighting system is viewed from certain oblique angles.

To facilitate the production of a lighting system comprising plurality of smaller light sources, a modular concept is employed, where each module, referred to as a lighting module, comprises a number of smaller light sources bundled together with a support structure (e.g. a PCB for providing electrical connection to each of the light sources), and light guides configured to direct the light from each of the light sources out from the lighting module. However, a drawback with a lighting system comprising a plurality of lighting modules arranged adjacent to each other is that the rigidity of the lighting system deteriorates, and the lighting system tends to bend at its weakest points: the connections between the lighting modules. Besides the aesthetic disadvantage of a bent lighting system, this may also cause a partial failure to the lighting system, such as an electrical and/or optical failure. An electrical failure generally results in that one or more light sources will fail to emit the desired amount of light, whereas an optical failure may result in stray light being emitted by the lighting system, thus failing to comply with the glare requirements set for the lighting system. A solution to this problem is disclosed in EP 1 650 729 A2, describing a display comprising a support structure holding a number of emissive lighting modules. The support structure may be used in large scale display applications, and provides a rigidity to the display. Each of the emissive lighting modules comprises among other things the components described above, i.e. a support substrate, an LED arranged onto the support structure, and light guides to direct the light from the LED out from the lighting module. However, when arranging the emissive lighting modules adjacent to each other, there will be a small spacing between the modules due to the support structures arranged between the emissive lighting modules, resulting in a pixilated appearance of the display. Therefore, such a solution is not suitable in a large area lighting system where a well defined uniform luminous flux is necessary. Using the support structure will furthermore make the lighting system heavy and bulky.

OBJECT OF THE INVENTION

There is therefore a need for an improved lighting system, and more specifically that overcome or at least alleviates the rigidity problems according to prior art, without deteriorating the uniform luminous flux of the overall lighting system.

SUMMARY OF THE INVENTION

According to an aspect of the invention, the above object is met by an optical system that comprises a multi-layer stack including a first layer comprising a plurality of adjacent optical components and a second layer comprising a plurality of adjacent optical components, the first and second layers being adapted to interact in order to provide a combined optical effect, wherein the layers are arranged in relation to each other such that at least one interface between optical components in the first optical layer is unaligned with all interfaces between optical components in said second optical layer.

The fact that at least one interface in one layer is unaligned with interfaces in the other layer will increase the structural strength of the system. This in turn provides for the ability to construct a large area optical system using smaller modular components based on the modular building concept. Such a modular building concept provides for the ability to create lighting systems of different forms and shapes, as compared to the generally rectangular structure used in common lighting systems using florescent tubes.

Each layer can comprise only two components. However, each layer can also comprises a plurality of adjacent optical components. For example, the components of the different layers can be arranged as a string (e.g. a one dimensional light stick) or in a more wider form (e.g. a wide spread two dimensional luminaire). The structural strength will of course be greater if more interfaces are unaligned, and preferably a plurality of interfaces between optical components in the first optical layer are unaligned with all interfaces between optical components in said second optical layer. The disadvantageous rigidity problems according to prior art can be overcome by arranging smaller elements of each layer in a brick- like manner, and arranging the layers in relation to each other such that interfaces between the elements of a layer do not overlap in parallel, i.e. coincide, with interfaces between the elements of another adjacent layer.

When using a plurality of components in one layer, essentially all interfaces in the first optical layer having a first orientation can be unaligned with all interfaces in the second optical layer having the same orientation. In addition to this, interfaces having a second orientation (typically perpendicular to the first orientation) can also be misaligned with interfaces having this second orientation.

The components in each layer can have different size, form and shape, such as a multi-angled form (e.g. a triangular element, a rectangular element, a pentagonal element, a hexagonal element, etc.). The components in a layer can also be arranged as interwoven comb-structures. By forming the components in the respective layers to have different sizes and/or shape, while at the same time taking into account the concept of non-coinciding interfaces, it is possible to even further improve the rigidity of the optical system. It is also possible to use components having similar shapes and forms in two adjacent layers, and rotate the elements in one layer in respect to the other.

Another advantage is that it will thus be possible to manufacture the different components in accordance to an optimal manufacturing process, rather than in accordance to a fixed overall width, breadth, or shape. The components in one arbitrary layer can have identical or different size, for example to be able to fill the empty spaces in one layer resulting from the brick-concept (e.g. similar to using half sized bricks at the edges when forming a constructional brick wall). The empty spaces might however also be ignored or filled with an appropriate filler material. Furthermore, it is not necessary to use the same type of components throughout an entire layer, but it is instead possible to include different types of components in one layer.

The optical components can be of any kind, and may include light emitting elements as well as components for changing optical properties of light. Such components include elements to adjust a wavelength distribution, an angular distribution, a spatial distribution, a polarization state of the received light, etc.

According to an embodiment of the invention, the optical system is used as a lighting system, in which case the first optical layer is a light emitting layer comprising a plurality of adjacent light emitting elements, and the second optical layer is a light guiding layer comprising a plurality of adjacent light guiding elements, each adapted to receive light emitted by at least one of said light emitting elements and to alter an optical property of said emitted light.

Such a lighting system will obtain an improved rigidity, while at the same time being able to emit light with uniform luminous flux. Furthermore, as the lighting system according to the present invention does not have to use a frame-work structure to achieve high rigidity, the light emitted by the lighting system will have a uniform appearance.

The light guiding layer can comprise at least two sub-layers, each sub-layer comprising a plurality of adjacent light guiding elements, wherein said sub-layers are arranged in relation to each other such that at least one interface between optical components in a first sub-layer and at least one interface between optical components in said second optical layer do not coincide with each other. The sub-layers can for example include at least one of a redirection layer (L3), a collimation layer and a diffuser layer.

The light emitting layer can comprise a substrate layer, comprising a plurality of substrate elements, each supporting at least one light source. In a preferred embodiment, each of the light emitting elements comprises a substrate and at least one light source for emitting light. The substrate can for example be formed by a PCB, by the substrate can also be a light guide, in which case the light source can be arranged onto the light guide. Generally, all of the light emitting elements are electrically connected with each other. The skilled addressee will however understand that it also is possible to provide individual control of each of the light emitting elements of the lighting system. Individual, or possibly section based, control of the light emitting elements can be advantageous for providing homogenous illumination of a room where natural ambient lighting from a window makes the part of the room closest to the window brighter than the part of the room farthest away from the window. An adjustable lighting system can compensate for such a difference. The light emitting elements can also be thermally connected to each other, such that heat generated when emitting light is spread over a larger surface.

Even though it is possible to use any type of compact light source, the light sources are preferably selected to be light emitting diodes (LED). Beyond standard and high intensity LEDs it is of course possible to use different types of LEDs, such as for example OLEDs, PLEDs, or a combination of different types of light sources. Furthermore, each of the light emitting elements can comprise a plurality of differently colored light sources. When using differently colored light sources, it might be necessary to increase the complexity of a control system for controlling the lighting system to include means for taking care of color shifts in the differently colored light sources due to temperature and aging.

It is advantageous to further include a redirection foil layer arranged in front of the light emitting layer at the side where light is to be directed out, the redirection foil layer comprising a plurality of redirection foil elements, wherein the redirection foil layer is positioned in relation to the light guiding layer such that at least one interface between the redirection foil elements and at least one interface between the light guiding elements do not coincide with each other. The redirecting foil layer is generally used to redirect any light escaping the light guides essentially parallel to the plane of the light guide to a direction essentially perpendicular to the plane. The introduction of a third layer is also advantageous from a rigidity perspective, as the brick-concept will be further enhanced by the third layer. The interfaces between the light guiding can be arranged to coincide with interfaces between the redirection foil elements, however, this is not necessary.

For protecting the lighting system from dust and/or dirt, the lighting system may further comprise an essentially transparent cover layer arranged in front of the above mentioned layers at the side where light is to be directed out, i.e. at the top of the multi-layer stack. As with the above mentioned different layers, the transparent cover layer can be based on a plurality of elements, however, it is preferred to use a single cover layer stretching over essentially the complete lighting system. Even though the above described lighting system is an advantageous alternative to a conventional light source, such as a luminaire, the lighting system is advantageously used as a component in for example, but not limited to, a backlight included in a display unit further comprising a display panel and a driver for individually controlling the above mentioned light sources such that the lighting system emits light at a desired brightness and color. As understood by the skilled addressee, the display panel is advantageously used as a substitute component in for example, but not limited to, a direct- view LCD (liquid crystal display) or an LCD-projector for TV application and/or monitor application.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing currently preferred embodiments of the invention, in which: Figure 1 is a partial side view of a multi-layer lighting system according to an embodiment of the present invention; and

Figure 2 is a simplified perspective sectional view of a lighting system similar to the multi- layer lighting system in figure 1.

DETAILED DESCRIPTION OF CURRENTLY PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, theses embodiment are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled addressee. Like reference characters refer to like elements throughout.

Referring now to the drawings and to figure 1 in particular, there is depicted a side view of a section of a multi- layer stacked lighting system 100 according to an embodiment of the present invention.

A first layer Ll, arranged at the bottom of the multi-layer stack, comprises a plurality of light emitting elements 102 in the form of substrate elements 101 arranged adjacent to each other. On top of each of the substrate elements 101 there is arranged a side- emitting light emitting diode (LED) 104, adapted to emit light when provided with a drive current. The drive current is provided by means of electrical connections 106 and 108. In the present embodiment the electrical connection 106, 108 are provided to all of the adjacent light emitting elements 102, such that all the light emitting elements 102 are connected to each other. It is however possible to implement an addressing strategy to be able to control each of, or a group of, LEDs 104 individually. In the present embodiment, the substrate elements 101 are constructed of multi- layered PCBs, and the connections 106, 108 are integrated inside of each of the substrate elements 101.

A second light guiding layer L2 is arranged on top of the first layer Ll. The second layer L2 comprises a plurality of different elements than the light emitting elements 102 in the first layer Ll, e.g. light guiding elements 110. In the present embodiment, each of the light guiding elements 110 includes three collimator strips 112 and a tripled- wedged light guide 114. The collimator strips 112 are adapted to receive light emitted by the LEDs 104, and to forward the emitted light into each of the tripled- wedged light guides 114. As in relation to the substrate elements 101, the light guiding elements 110 are arranged adjacent to each other, but positioned in such a way that interfaces between the light guiding elements 110 do not coincide with interfaces between the light emitting elements 102. As understood by the skilled addressee, any number of wedges (in the present embodiment three) can be used, thereby making it possible to form light guiding elements 110 having different dimensions. The adjacently positioned tripled- wedged light guide 114 are optically connected with each other in the sense that light is able to be travel from one light guide to the other. However, they do not have optical contact in the sense that the light guides are connected by a transparent material (e.g. glue) with a refractive index that more-or-less matches that of the light guides. Hence there will always be air slits or cavities between the tripled- wedged light guide 114. Glue or any other similar materials in optical contact with the light guides will lead to light losses and unwanted stray light. Instead, the light guides has to loosely connected with each other.

The lighting system 100 further comprises a third layer L3 arranged on top of the second layer L2. The third layer L3, which in the present embodiment is a redirection foil layer, comprises a plurality of redirection foil elements 116 used to redirect the light that escapes the tripled- wedged light guide 114 essentially parallel to the plane in a direction that is essentially perpendicular to the longitudinal plane of the lighting system 100.

The redirection foil elements 116 are positioned such that interfaces between the redirection foil elements 116 in the third layer L3 and interfaces between the substrate elements 101 in the first layer Ll coincide with each other. The described positioning of interfaces between the adjacently positioned elements (i.e. substrate elements 101, light guiding elements 110, and redirection foil elements 116, respectively) in each of the stacked layers Ll - L3 provides for an optimal distribution of the interfaces, thereby providing a rigid brick- like construction. However, it is of course possible to arrange the interfaces such that none of the interfaces in one of the layers coincide with any interfaces of the any of the other layers. The exact placement of interfaces can instead depend on the construction of the different elements of the respective different layers, as long as the positioning of the majority of interfaces in two adjacently stacked layers do not coincide with each other. Furthermore, a transparent plate 118 is provided on top of the lighting system

100 for providing protection against dust and/or dirt. The transparent plate 118 is preferably in the form of a single plate covering the whole visible area of the lighting system 100. As understood by the skilled addressee, it is of course possible to use a different structure than the above mentioned arrangement without departing from the scope of the invention. For example, it is possible to only use two different layers covered by a transparent protection plate 118.

During operation, as soon as the LED 104 receives the drive current through the electrical connections 106, 108, the side-emitting LED 104 starts to emit light. The light from the side-emitting LED 104 impinges onto a collimator strip 112, which directs the light to a wedge of the wedged light guide 114. The light transferred to the wedged light guide 114 will then be coupled to the redirection foil element 116 which the will redirect the light being out coupled from the wedged light guide 114, such that it is out coupled from the lighting system 100 in a direction essentially perpendicular to the longitudinal plane of the lighting system 100. Figure 2 illustrates a perspective sectional view of a similar multi-layer lighting system 200 as the lighting system 100 illustrated in figure 1. For better understanding and for simplicity of explanation, the elements of the three different layers Ll - L3 (e.g. light emitting elements 102, light guiding elements 110, and redirection foil elements 116) are illustrated as sectional blocks. However, the respective block-elements 102, 110, and 116 still comprises similar components as describe above in relation to figure 1 (e.g. the light emitting element 102 comprises a light source).

To further illustrate the possibility to use different dimensions, forms and shapes for the block-elements of the different layers, the first layer Ll is illustrated to comprise squared light emitting elements 102, while the second layer L2 comprises light guiding elements 110 covering the total width and only a part of the total breadth of the lighting system. Further, the third layer L3 comprises redirection foil elements 116 arranged in a honeycomb-pattern. As in figure 1 , the lighting system 200 is covered by a transparent plate 118. It is according to the selection of the dimensional sizes and the placement of the block-elements 102, 110, and 116 in the different layers Ll - L3 possible to provide a lighting system 200 wherein a majority of interfaces between the different block-elements 102, 110, and 116 of the different layers Ll - L3 are arranged to not coincide with each other. The above discussed positioning of the different block-elements 102, 110, and 116 is especially advantageous for providing a lighting system 200 with improved rigidity.

The skilled addressee realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, it is possible to include more than one light source with each substrate portion. It is also possible to include differently colored light sources, such as LEDs, which thereby would make it possible to emit light with a plurality of colors and color temperature. However, when using differently colored LEDs, it might be necessary to adapt the lighting system to include means for handling differences in the surrounding temperature and/or the temperature of the LED in comparison to a predetermined normal temperature, as a difference in temperature generally renders a shift in color.

Furthermore, the above description describes a lighting system comprising a limited number of different layers (i.e. two to four), however, the skilled addressee understand that different optical and/or mechanical functionality can be either combined or split up, and the principle of the present invention can be used in combination with any number of different layers.

In conclusion, it is according to the present invention possible to provide a large scale lighting system based on a modular building concept which has a maintained rigidity in comparison to a prior art large scale lighting system. The modular layer portions (e.g. light emitting elements, light guiding elements, redirection foil elements, and etc.) of each of loosely stacked layers are positioned such that the interfaces between elements of two adjacently stacked layers do not coincide with each other.

Claims

CLAIMS:

1. An optical system (100, 200) comprising a multi-layer stack including:

- a first layer (Ll) comprising a plurality of adjacent optical components (102); and

- a second layer (L2) comprising a plurality of adjacent optical components (110), said first and second layers being adapted to interact in order to provide a combined optical effect, wherein said layers (Ll, L2) are arranged in relation to each other such that at least one interface between optical components in said first optical layer, is unaligned with all interfaces between optical components in said second optical layer.

2. The optical system as claimed in claim 1, wherein a plurality of interfaces between optical components in said first optical layer are unaligned with all interfaces between optical components in said second optical layer.

3. The optical system as claimed in claim 2, wherein essentially all interfaces in said first optical layer having a first orientation are unaligned with all interfaces in said second optical layer having said orientation.

4. The optical system as claimed in claim 1, wherein the size of an optical component in said first layer (Ll) is different than the size of an optical component in said second layer (L2).

5. The optical system as claimed in claim 1, wherein the shape of an optical component in said first layer (Ll) is different than the size of an optical component in said second layer (L2).

6. A lighting system comprising an optical system as claimed in claim 1, wherein the first optical layer is a light emitting layer (Ll) comprising a plurality of adjacent light emitting elements (102); and the second optical layer is a light guiding layer (L2) comprising a plurality of adjacent light guiding elements (110), each adapted to receive light emitted by at least one of said light emitting elements (102) and to alter an optical property of said emitted light.

7. The lighting system as claimed in claim 6, wherein said light guiding layer (L2) comprises at least two sub-layers (L2, L3), each sub-layer comprising a plurality of adjacent light guiding elements (110, 116), wherein said sub-layers are arranged in relation to each other such that at least one interface between optical components in a first sub-layer and at least one interface between optical components in said second optical layer do not coincide with each other.

8. The lighting system as claimed in claim 7, wherein one of said sub-layers is selected from the group consisting of redirection layer (L3), collimation layer and diffuser layer.

9. The lighting system as claimed in one of claims 6-8, wherein said light emitting layer comprises a substrate layer, comprising a plurality of substrate elements, each supporting at least one light source.

10. The lighting system as claimed in claim 9, wherein said substrate layer is arranged to provide electrical connection between said light sources.

11. The lighting system as claimed in claim 9, wherein said substrate elements are light guide elements.

12. The lighting system as claimed in claim 9, further comprising a thermal layer, comprising a plurality of heat sink elements thermally connected to said light sources.