WO2008152558A1

WO2008152558A1 - Improved lighting device

Info

Publication number: WO2008152558A1
Application number: PCT/IB2008/052252
Authority: WO
Inventors: Liesbeth Van Pieterson; Petrus C. P. Bouten; Hugo J. Cornelissen; Martijn Krans; Jan C. Kriege
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-06-15
Filing date: 2008-06-09
Publication date: 2008-12-18
Also published as: TW200925517A

Abstract

A lighting device comprises a first layer comprising a plurality of light sources that are distributed in a two-dimensional pattern and attached to a sheet of textile- like material, and a second layer comprising a plurality of flexible ribbons having a refracting structure, where at least a subset of the ribbons are arranged parallel with each other and arranged in relation to the sheet of textile-like material such that light emitted from the light sources is refracted by the ribbons. Such a lighting device is an improvement over prior art arrangements at least in that the inherent flexibility of a photonic textile-like material can be fully utilized in different applications, while at the same time the homogeneity of the distribution of the light emitted from the device can be high.

Description

Improved lighting device

TECHNICAL FIELD

The present invention relates to a lighting device comprising plurality of light sources that are distributed in a two-dimensional pattern and attached to a sheet of textile-like material.

BACKGROUND

In recent years, attempts have been made to change passive textiles into intelligent and interactive systems by the integration of electronics. These have sometimes been named "photonic textiles" and they typically comprise arrays of light sources, such as inorganic LEDs, that are integrated into fabrics without compromising the soft look and feel of the textile material. Examples of fields of application of these photonic textiles include a cushion display, interactive cubes, backpack and jackets. In addition, photonic textiles are interesting from a medical point of view. That is, photonic therapy, such as investigated for acne treatment, wound healing, pain relief, baby jaundice etc. are also important fields of use. However, the fact that inorganic LEDs are typically used as light sources in these devices often leads to a problem that is related to the fact that inorganic LEDs are point source emitters. A fabric with LEDs attached to it at certain spacing, has no appealing look. Also for medical therapy applications it is important that the light is more or less homogeneously distributed over the textile area. Regarding LCD backlight systems, light direction foils, such as the Vikuiti™ display enhancement films of 3M corporation, are used that consist of prismatic ribbons. Another example of a similar foil can be found in European patent application publication EP 0609816.

When such prior art foils are arranged on top of a light source in the form of a LED, the central LED spot is redirected such that it will be viewed as two satellite light spots. Using two crossed foils, four spots can be produced, etc. However, an unfortunate drawback with such foils is that the flexibility of the foils differs significantly from that of textile-like materials. Textile-like materials more easily adopt 3-D shapes (deformation along two axes). In general, foils can be deformed well around one axis, but not around two axes. SUMMARY

An object is hence to overcome drawbacks with prior art solutions. Such an object is achieved by lighting device as in the appended claims.

Hence, there is provided a lighting device that comprises a first layer comprising a plurality of light sources that are distributed in a two-dimensional pattern and attached to a sheet of textile-like material, and a second layer comprising a plurality of flexible ribbons having a refracting structure, where at least a subset of the ribbons are arranged parallel with each other and arranged in relation to the sheet of textile-like material such that light emitted from the light sources is refracted by the ribbons. Such a lighting device is an improvement over prior art arrangements at least in that the inherent flexibility of a photonic textile- like material can be fully utilized in different applications, while at the same time the homogeneity of the distribution of the light emitted from the device can be high.

The second layer may comprise a first subset of refractive parallel ribbons aligned along a first direction and a second subset of refractive parallel ribbons aligned along a second direction, where the first direction is not equal to the second direction. For example, the first direction may perpendicular to the second direction.

Alternatively, the second layer may comprise a first subset of refractive parallel ribbons aligned along a first direction and a second subset of parallel ribbons aligned along a second direction, where the first direction is not equal to the second direction. For example, the first direction may perpendicular to the second direction. From a constructional point of view such a second subset of ribbons that are not refractive, e.g. yarns and/or fibres, may function as a fixation/interlocking structure.

The first subset of parallel ribbons and the second subset of parallel ribbons may form a woven structure or a braided structure. These are examples of features that further improve the flexibility of the device.

The ratio between the width and the thickness of at least one ribbon may be at least five. It has been found that such a limit on the width to thickness ratio is preferable in order to obtain as high flexibility as possible. At least one of the ribbons may be configured such that the thickness and/or the width of the ribbon varies along a direction perpendicular to the direction of extension of the ribbon. Such a configuration may be such that the ribbons are thinner in between the light sources, which even further enhances the flexibility of the ribbon and also reduces the unwanted light guiding in the ribbon itself, and also be helpful for mechanical interlocking of the ribbons within a structure.

Moreover, at least one of the ribbons may be configured with a plurality of cut-outs along a direction perpendicular to the direction of extension of the ribbon. Similarly, at least one of the ribbons may be configured with a plurality of individual refracting elements interconnected with flexible structures along the direction of extension of the ribbon.

At least one of the ribbons may comprise a stretch limiting structure. This stretch limiting structure may comprise a fibre of a material having a high tensile modulus, e.g. >500 MPa, and be incorporated into the at least one ribbon. The stretch limiting structure may also, or alternatively, comprise a sheet of a material having a high tensile modulus.

The spatial relationship between the two layers of the device may be such that the first layer is arranged on the second layer. The layers may alternatively be arranged such that the first and the second layer are arranged into a single composite layer. The textile-like material may comprise any of a woven material, a non- woven material and a flex film material as well as any combination of these materials. In other words, there is provided a photonic textile-like device that overcomes drawbacks with prior art solutions.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure Ia schematically shows a perspective view of a first embodiment of a lighting device comprising a woven ribbon structure.

Figure Ib schematically shows a top view of a part of the lighting device illustrated in figure Ia. Figure Ic schematically shows a cross section of a part of the lighting device illustrated in figure Ia.

Figure 2 schematically shows a cross section of a part of a second embodiment of a lighting device.

Figure 3 a schematically shows a cross section of a part of a third embodiment o f a lighting device .

Figure 3b schematically shows a perspective view of a refracting structure comprised in the lighting device illustrated in figure 3 a.

Figure 4 schematically shows a ribbon that varies in width along a direction of extension of the ribbon. Figure 5 schematically shows a first example of a ribbon that comprises cutouts along a direction of extension of the ribbon.

Figure 6 schematically shows a second example of a ribbon that comprises cut-outs along a direction of extension of the ribbon. Figures 7, 8 and 9 schematically illustrate examples of ribbons provided with stretch limiting structures.

DETAILED DESCRIPTION OF EMBODIMENTS

Figures Ia, Ib and Ic are illustrations, schematically drawn, of an embodiment of a lighting device. Figure Ib is a partial top view and figure Ic is a cross sectional partial view of the section indicated with A in figure Ia. A sheet or layer of a reflective, e.g. white, textile-like material 102 is provided with a plurality of light sources, such as LEDs, of which only one single light source 108 is shown. The light sources are provided with electric power via a suitably configured electrode pattern 105 that is connected to a power source 106. The electrode pattern 105 and the power source 106 may be configured in any suitable manner, for example in a simple manner where all light sources are connected in parallel, or in a more complex manner such that any number of light sources may be addressed individually and powered on and off as desired.

A plurality of ribbons 103, 104 are arranged on top of the sheet 102 and arranged such that the light sources are sandwiched between the sheet 102 and the ribbons. A suitable material for the ribbons is Polydimethylsiloxane (PDMS) although other materials may also be used, such as polycarbonate, PMMA, PET, PEN etc. The ribbons are transparent and provided with a refracting prismatic structure 110, the structure having 90 degree apex angles. In the example shown in figure 1, the refracting structure is on one side of the ribbons. However, other examples of ribbons may have other forms of structures located on any or both sides.

The light 109 emitted by the light sources, as exemplified by the single light source 108, is refracted by the structure 110 of the ribbons and exits in a general direction z, as exemplified in figure Ic. Due to total internal reflection 117, virtually no light exits the ribbon 104 in an area immediately above the light source 108, as generally indicated by reference numeral 113. However, light 139, 149 exiting from the light source in directions that are more along the +/-x directions is refracted by the refracting structure 110 and exits from the ribbons along directions 112 and 114. From a viewer's point of view, looking from above the device 100 along the -z direction, this will generate an appearance that, in the x- direction, is a respective image 120 and 122 of the light source 108.

As indicated in figure Ia, the ribbons indicated with the exemplifying ribbonl03 are arranged in a perpendicular relation to the ribbon 104 discussed above. Here the ribbons are woven together and form an essentially flat sheet on top of the textile-like sheet 102. The ribbon 103 is in this example identical in structure to the ribbon 104 and, consequently, refracts the light in the same way as described above. This results in an appearance as illustrated in figure Ib where also two images 124 and 126 of the light source 108 are shown. In other words, the light 109 emitted from the light source 108 has been spread out into four images and thereby the overall appearance of the lighting device has a more homogeneous character than that of a device without the refracting ribbons. The flexibility of the device 100 can be optimized by a suitable selection of width and thickness for the ribbons. It has been found that for PDMS ribbons, a ratio between the width and the thickness of at least five gives a good result. Furthermore, an alternative way of arranging the ribbons is braiding.

Although figure 1 illustrates a device having two sets of refracting parallel ribbons that are woven into each other, it is not always necessary that the both sets of parallel ribbons also contain the refracting structures. From a constructional point of view a second set of ribbons may have only a function of fixation/interlocking. In such a case, also more simple structures may be used instead, such as yarns and/or fibres.

Furthermore, in order to obtain an appropriate bending stiffness of the device 100, either thin high tensile modulus materials or thicker low tensile modulus materials may be used for the ribbons. Alternatively, as will be described below in connection with figures 7 to 9, strengthening structures may be arranged in relation to the ribbons.

Turning now to figure 2, an alternative refracting structure to that of the structure 110 in figure 1, will be described. Instead of a prismatic structure, as in figure 1, figure 2 illustrates a Fresnel-like structure. Figure 2 is a cross sectional view of a small part of a ribbon, similar to the ribbons described above and, e.g., made of PDMS. A light source 208, such as a LED, is illustrated being attached to a textile-like sheet 202 and emitting light 209.

Similar to the situation of figure 1, the light 209 emitted by the light source 208 is refracted by the Fresnel-like structure 210 of the ribbons and exits in a general direction z. However, contrary to the situation of figure 1, there is no total internal reflection in the ribbon 204, and light exits the ribbon 204 also in an area immediately above the light source 208, as generally indicated by reference numeral 213. Moreover, light exiting from the light source in directions that are more along the +/-x directions is refracted by the refracting structure 210 and exits from the ribbons along direction 212. From a viewer's point of view, looking from above a device having such refracting ribbons 204 along the -z direction, this will generate an appearance that is a spread out image 220 of the light source 208.

Turning now to figures 3 a and 3b, another alternative refracting structure to that of the structure 110 in figure 1, will be described. Instead of ribbons having a prismatic structure, as in figure 1, figures 3 a and 3b illustrate a sheet-like structure of interconnected multi- faceted pyramids 310. Figure 3a is a cross sectional view of a small part of such a sheet, e.g., made of PDMS, and figure 3b is a perspective view of such a sheet. The pyramids are interconnected with thin ribbons 333 made of a suitably selected material. Light sources 308, 338 and 348, typically in the form of LEDs, are illustrated being attached to a textile- like sheet 302 and emitting light 309. A shown in figure 3a, each LED is arranged such that it is aligned in the x direction and y direction with a respective refracting pyramid.

Similar to the situations described above, the light 309 emitted by the light sources 308, 338 and 348 is refracted by the pyramid structures 310 and exits in a general direction z. Similar to the situation of figure 2, there is no total internal reflection in the refracting structures 310 and light exits the refracting structures 310 also in areas immediately above the light sources 308, 338, 348, as generally indicated by reference numeral 313 above the light source 308. Moreover, light exiting from the light sources in directions that are more along the +/-x directions is refracted by the refracting structure 310 and exits along a plurality of directions 312. From a viewer's point of view, looking from above a device having such refracting structures 310 along the -z direction, this will generate an appearance that is a plurality of images, such as images 320 and 322, of the light sources 308, 338, 348.

As illustrated in figures 1-3 a lighting device may be configured such that a first layer is arranged on a second layer. It should be noted that alternative arrangement include those where also a third transparent layer is arranged between the first layer and the second layer. Such arrangement will provide a spacing between the light sources and the refracting layer and improve the optical performance of the device. Furthermore, another alternative is to arrange the first layer and the second layer into a single composite layer.

Turning now to figures 4, 5 and 6, examples of ribbons having local reducetions of the thickness and/or width that give the ribbons a decreased flexural rigidity and thereby being more bendable. This increased flexibility may be realised in various ways and one example is shown in figure 4, where a ribbon 401 is configured with cut-outs 402 at regular intervals such that the width of the ribbon 401 varies along a direction perpendicular to the direction of extension of the ribbon 401. Another example is shown in figure 5, where a ribbon 501 is configured with a plurality of cut-outs 502 in the form of rounded holes along the ribbon. Figure 6 illustrates a similar ribbon 601 having rectangular cut-outs 602.

With regard to all examples described above, although high flexibility of the refractive ribbons is desirable, extensive stretching of the ribbons may distort their optical performance. In various applications a good bending behaviour may be required, but a limitation of the stretching may be necessary. To obtain such performance, the ribbons may be provided with stretch limiting structures, such as a fibre of a material having a high tensile modulus. Such a fibre may be incorporated into the ribbon or simply attached in a parallel relation to a ribbon. A stretch limiting structure may also be in the form of a sheet or ribbon of a material having a high tensile modulus.

Figures 7, 8 and 9 are cross sectional views that schematically illustrate examples of ribbons provided with such stretch limiting structures. Hence, figure 7 shows a cross sectional view of a refractive ribbon 704, the view being perpendicular to the direction of extension of the ribbon (i.e. perpendicular to the views in figures Ic, 2 and 3a). Fibres 761 and 762 are attached to the ribbon 704. Figure 8 shows a ribbon 804 into which stretch limiting structures in the form of fibres 861 and 862 have been incorporated.

As figure 9 shows, to limit the stretching of a ribbon 904, but preserving a good bend ability, the ribbon 904 is a multi-layer structure. A lower layer 961 is a thin high modulus polymer, for instance a 25 micron PET foil. The refracttive part of the ribbon 904 is, as in previous examples, typically a PDMS layer and it's thickness may be significantly larger than that of the lower layer 961.

It should be noted that the structures described above with reference to figures 2-9 may, individually or in any combination, form part of a lighting device, such as the lighting device 100 of figure 1. Fields of use of a lighting device as described above include dynamic interior lighting systems (e.g. furniture upholsteries, curtains, carpets), as well as wearable communication displays (e.g. in backs, jackets), photonic therapy devices (baby jaundice sleeping back, acne treating t-shirt, wound healing plaster, etc.).

Claims

CLAIMS:

1. A lighting device (100) comprising:

- a first layer comprising a plurality of light sources (108, 208, 308) that are distributed in a two-dimensional pattern and attached to a sheet of textile-like material (102, 202, 302), and - a second layer comprising a plurality of flexible ribbons (103, 104, 204, 304,

401, 501, 601, 704, 804, 904) having a refracting structure (110, 210, 310), where at least a subset of the ribbons are arranged parallel with each other and arranged in relation to the sheet of textile-like material such that light emitted from the light sources is refracted by the ribbons.

2. The lighting device of claim 1, where the second layer comprises a first subset of refractive parallel ribbons aligned along a first direction and a second subset of refractive parallel ribbons aligned along a second direction, where the first direction is not equal to the second direction.

3. The lighting device of claim 1, where the second layer comprises a first subset of refractive parallel ribbons aligned along a first direction and a second subset of parallel ribbons aligned along a second direction, where the first direction is not equal to the second direction.

4. The lighting device of claim 2 or 3, where the first direction is perpendicular to the second direction.

5. The lighting device of any of claims 2 to 4, where the first subset of parallel ribbons and the second subset of parallel ribbons form a woven structure.

6. The lighting device of any of claims 2 to 4, where the first subset of parallel ribbons and the second subset of parallel ribbons form a braided structure.

7. The lighting device of any of claims 1 to 6, where the ratio between the width and the thickness of at least one ribbon is at least five.

8. The lighting device of any of claims 1 to 7, where at least one of the ribbons is configured such that the thickness of the ribbon varies along a direction perpendicular to the direction of extension of the ribbon.

9. The lighting device of any of claims 1 to 8, where at least one of the ribbons is configured such that the width of the ribbon (401) varies along a direction perpendicular to the direction of extension of the ribbon.

10. The lighting device of any of claims 1 to 9, where at least one of the ribbons is configured with a plurality of cut-outs (502, 602) along a direction perpendicular to the direction of extension of the ribbon.

11. The lighting device of any of claims 1 to 10, where at least one of the ribbons is configured with a plurality of individual refracting elements (310) interconnected with flexible structures (333) along the direction of extension of the ribbon.

12. The lighting device of any of claims 1 to 11, where at least one of the ribbons comprises a stretch limiting structure (761, 762, 861, 862,961).

13. The lighting device of claim 12, where the stretch limiting structure comprises a fibre of a material having a high tensile modulus.

14. The lighting device of claim 13, where the fibre of a material having a high tensile modulus is incorporated into the at least one ribbon.

15. The lighting device of any of claims 12 to 14, where the stretch limiting structure comprises a sheet of a material having a high tensile modulus.

16. The lighting device of any of claims 1 to 15, where the first layer is arranged on the second layer.

17. The lighting device of claim 16, comprising a third transparent layer arranged between the first layer and the second layer.

18. The lighting device of any of claims 1 to 15, where the first layer and the second layer are arranged into a single composite layer.

19. The lighting device of any of claims 1 to 18, where the textile-like material comprises a woven material.

20. The lighting device of any of claims 1 to 19, where the textile-like material comprises a non- woven material.

21. The lighting device of any of claims 1 to 20, where the textile-like material comprises a flex film material.