WO2008139386A1

WO2008139386A1 - Moiré effect lumination device

Info

Publication number: WO2008139386A1
Application number: PCT/IB2008/051812
Authority: WO
Inventors: Marcellinus P. C. M. Krijn; Siebe T. De Zwart; Martin G. H. Hiddink; Michel C. J. M. Vissenberg; Ariadne D. Tenner; Joseph L. A. M. Sormani
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-05-14
Filing date: 2008-05-08
Publication date: 2008-11-20
Also published as: TW200914760A

Abstract

Proposed is a Moiré effect lumination device (1), comprising a housing (10) with an optically transparent window (11), a grid (20) with a periodicity λg arranged in optical relationship with the transparent window (11), and the housing comprising a light source (30). The Moiré effect lumination device (1) is characterized in that the light source (30) comprises an array of light emitting elements (31) with a periodicity λls. This is especially advantageous as the Moiré effect can now be realized through the interference effect of the grid and the array of light emitting elements. Preferably, the grid is provided with a lenticular or lenslet array or with color filters. Preferably the color filters (60) comprise electrically controllable liquid crystal cells enabling a dynamic Moiré effect.

Description

Moire effect lumination device

FIELD OF THE INVENTION

The invention relates to a Moire effect lumination device comprising a housing with an optically transparent window, the housing comprising a light source, and a grid with a periodicity λ_g arranged in optical relationship with the transparent window. The invention also relates to a method for creating a Moire effect. Such Moire effect lumination devices and Moire effect creation methods are used in particular for decorative purposes.

BACKGROUND OF THE INVENTION

An embodiment of a Moire effect lumination device of the kind set forth is known from US4300068 by Baird et al. That document discloses an incandescent lamp bulb envelope for creating a Moire effect that has a plurality of transparent and nontransparent regions on its surface. When viewed from a point external to the envelope, the individual nontransparent regions on the surface of the envelope which is nearest to the point appear as superimposed upon and intersecting with nontransparent regions on the surface furthest from the point. The nontransparent regions may be either light diffusive (i.e. translucent) or light nontransmissive (i.e. opaque) in nature.

The advantage of this approach lies in the fact that the apparent intersections produce a Moire effect, which is enhanced by varying the line of sight to the bulb. Hence, the device creates a highly decorative effect. A drawback of the solution described in US4300068, however, is that the device needs two superimposed grids of transparent and nontransparent regions to create the Moire effect. This makes the device relatively complex and reduces the design freedom for these decorative devices. For instance, as a consequence of applying the grids on the incandescent lamp bulb surface, the Moire effect only visualizes when looking through the bulb.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a Moire effect lumination device of the kind set forth, in which only a single grid is applied. This object is achieved with the Moire effect lumination device according to the invention as defined in claim 1. According to an aspect of the invention the light source comprises an array of light emitting elements with a periodicity λ_ls. Advantageously the interference of the array of light emitting elements and the grid results in a visible Moire effect. Thus, the invention provides a much simpler construction for a Moire effect lumination device by eliminating the need of a second grid to create the Moire effect. Additionally, the Moire effect lumination device according to the invention advantageously can be designed as a non-look-trough decorative appliance.

In an embodiment of the present invention the light emitting elements are chosen to emit light with at least two spectra. Preferably the light emitting elements are arranged in at least a first array emitting light with a first spectrum and having a periodicity λ_1Sjl and at least a second array emitting light with a second spectrum and having a periodicity λ_ls,₂. Advantageously, the Moire effect will be constituted by Moire patterns of the individual spectral colors.

In an embodiment, periodicities λ_ls or λ_g depend on the location an the array of light emitting elements and the grid, respectively. Advantageously this embodiment enhances the decorative effect.

In an embodiment of the Moire effect lumination device according to the invention the grid is provided with optical lenses having a periodicity X₁. Applying the optical lenses has the advantage that the array of light emitting elements is demagnified forming an array of virtual light emitting elements. As an advantage the Moire effect can be created with a smaller number of light emitting elements.

In an embodiment of the invention the light emitting elements are LEDs. The low spatial extension of LEDs allows advantageously for a small periodicity of the array of light emitting elements.

In an embodiment the grid is provided with color filters. Preferably, the color filters comprise at least a first set of color filters having a first optical filtering characteristic and a periodicity X^₁ and at least a second set of color filters having a second optical filtering characteristic and a periodicity X^₂. Applying color filters advantageously results in the Moire effect to be constituted by Moire patterns of the individual spectral colors.

In an embodiment the color filters comprise liquid crystal cells. Preferably, the liquid crystal cells are arranged to be controllable enabling a dynamic Moire effect. Advantageously, the viewer observes a dynamic Moire pattern - even without repositioning himself- in accordance with the electrical control of the liquid crystal cells.

According to another aspect the invention provides a method for creating a Moire pattern as defined in claim 10. The method comprises the steps of providing a light source, providing a grid with a periodicity λ_g arranged in optical relationship to the light source, and wherein the light source comprises an array of light emitting elements with a periodicity λ_ls. The method has the advantage that only a single grid is needed to create a Moire pattern, since the function of the traditionally essential second grid is provided by the array of light emitting elements.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, features and advantages of the invention are disclosed in the following description of exemplary and preferred embodiments in connection with the drawings.

Fig. 1 shows a top view of an embodiment according to the invention

Fig. 2 graphically depicts the periodicity and wave -vector of a grid (front view)

Fig. 3 shows a top view of an embodiment according to the invention comprising multiple arrays of different colored light emitting elements

Fig. 4 shows a top view of an embodiment according to the invention comprising an array of lenses

Fig. 5 shows a top view of an embodiment according to the invention with a grid comprising optical filters

Fig. 6 shows a top view of an embodiment according to the invention with a grid comprising multiple arrays of optical filters with different filtering characteristics

DETAILED DESCRIPTION OF THE EMBODIMENTS

Fig. 1 shows a top view of a Moire effect luminance device 1 according to the invention, comprising a housing 10 with an optically transparent window 11, the housing comprising a light source 30, and a grid 20 with a periodicity λ_g arranged in optical relationship with the transparent window 11. The light source 30 comprises an array of light emitting elements 31 with a periodicity λ_ls. Advantageously, the interference of the light source 30 and the grid 20 patterns create the Moire effect of this embodiment. The grid 20 may be created in a wide variety of ways. For instance, it may be constructed as a separate entity inside the housing 10. Advantageously, however, the grid 20 is applied on or adjacent to the transparent window 11 or by abrading the (inside or outside) surface of the window. Alternatively, it may be created by applying an opaque or diffusive coating onto the surface of the window 11.

In general, a Moire pattern is an interference pattern created, for example, when two periodic grids 20 are overlaid having a slightly different grid period or when two grids 20 with equal periodicity are overlaid at an angle with respect to each other. A periodic grid 20 is characterized by a wave vector k , located in the plane of the grid and directed perpendicular to the grid pattern (Fig. 2). The relation between the length of the wave-vector and the associated grid period, λ_g, is given by

The Moire pattern, characterized by a wave vector k_M , resulting from overlaying two grids 20 follows simply from the relation k — k — k ?

According to the invention, the first wave-vector relates to the array of light emitting elements 31, while the second relates to the grid 20. Equation 2 implies that two identical non tilted grids 20 will not produce a Moire pattern. Two identical non tilted grids 20 spaced apart at a distance d and viewed from a distance D, however, will produce a Moire pattern characterized by κ, -~-^λ d, T , „ d. k₂ (D + -) - k_γ (D --)

D 2 ' ^{L v} T

A viewer moving towards (away from) the grids 20 will observe a dynamic Moire pattern, which period X_M will decrease (increase), as under most practical circumstances d«D. For a viewer moving in a direction parallel to the planes of the two grids 20, the Moire pattern will appear to move at a velocity V_M that may differ from the viewer's velocity v_v. In fact, even the direction of movement may differ, as the velocities are related by the expression

V M_M ~ V v _{p D} 4

where

p = d - ^λ<-¹ λg,2 - \,l Figs. 1 and 2 show the light source 30 and the grid 20 to have a periodicity in only 1 dimension (i.e. have a single wave-vector £ .) It is noted however that they may have a periodicity in 2 dimensions. In fact, the periodicity may vary as a function of location on the grid 20 or light source 30.

The light emitting elements 31 may all emit the same spectrum or may consist of different sets, with each set emitting light with a different spectrum. Therefore, in an embodiment according to the invention as shown in Fig. 3, the light source 30 comprises at least two arrays 41,42 of light emitting elements 31, each array emitting light with a different spectrum. Hence the array of light emitting elements 31 can be subdivided into at least a first array 41 emitting light with a first spectrum and having a periodicity λ_1Sjl and in at least a second array 42 emitting light with a second spectrum and having a periodicity λ_1Sj2. Of course, the array of light emitting elements 31 may comprise a third array 43 emitting light with a third spectrum and having a periodicity λ_lsj3, and so on. The individual periodicities λis,i, λ_1Sj2, λ_lsj3, etc may be equal or may differ, depending on the Moire effect to be designed. Advantageously, the resulting Moire effect comprises the overlapping Moire effects in the individual spectral colors, thus contributing to the decorative effect.

Preferably the light emitting elements 31 comprise light emitting diodes (LEDs), although it is understood that in principle any light source technology can be used - such as (filtered) incandescent bulbs, (compact) fluorescent tubes, organic LEDs, etc. The LEDs may or may not be comprise a color converting medium, such as a phosphor. Advantageously, the phosphor coated (pc-)LEDs emit a wide spectrum (including white light), while the non-pcLEDs emit a narrow band spectrum, selectable throughout the visible spectrum.

In an embodiment of the invention as indicated in Fig. 4 the Moire effect luminance device 1 may comprise, in addition to the grid 20, an array of optical lenses 50 demagnifying the real array(s) 41,42 of light emitting elements 31 with periodicities λ_1Sjl, λ_1Sj2 into virtual array(s) 46,47 with periodicities λ'_1Sil, λ'_ls,₂. Alternatively, the grid 20 is provided with optical lenses 50 having a periodicity λ_ls so as to create a lenticular (i.e. a ID array of cylinder lenses) or lenslet array (i.e. a 2D array of round or polygonal lenses). In other words, the grid 20 and the optical lenses 50 may be integrated into one entity, with for instance the grid being grinded or coated on the lenticular or lenslet array. Given the object distance L₀ from the light emitting elements 31 to the optical lenses 50 with focal length/, the image distance L₁ can be approximated by L = L f

⁰ L₀ - /

Preferably the geometrical patterns of the array(s) 41,42 of light emitting elements 31 and the array of optical lenses 50 are chosen such that the virtual images of the light emitting elements 31 of the same spectral color coincide (Fig. 4). Advantageously the interference between the light originating form the virtual array(s) 46,47 and the grid 20 creates the Moire effect. The embodiment has the advantage that a Moire effect luminance device 1 can be created with a smaller number of light emitting elements 31. In one embodiment the window 11, grid 20, and lens array 50 preferably are incorporated in a single entity, resulting in the virtual array(s) 46, 47 being located outside the housing 10 of the Moire effect luminance device 1. This enhances the decorative effect and stimulates the imagination of the viewer.

In another embodiment according to the invention, the grid 20 is provided with color filters 60 (Fig. 5). Preferably the filters are applied as a coating or layer on the transparent window 11. The color filters 60 transmit a predetermined part of the spectrum emitted by the light emitting elements 31 , while absorbing the complementary part. Alternatively, the color filters 60 may transmit a predetermined part of the spectrum, while reflecting the complementary part. Such filters are often referred to as dichroic filters or dichroic mirrors. The reflected light can be recycled inside the housing 10 to allow it to pass a different color filter 60. The filter characteristic can selectably be chosen throughout the visible spectrum so that the filter 60 transmits predominantly red, amber, green, blue, etc. Hence, the, layer may comprise sections that transmit light in accordance with the filter characteristic and opaque sections blocking light.

In another embodiment according to the invention, the grid is provided with color filters 60 having different filtering characteristics (Fig. 6). Preferably, the grid is provided with at least a first set of color filters 61 having a first optical filtering characteristic and a periodicity λ_cf,i and at least a second set of color filters 62 having a second optical filtering characteristic and a periodicity λ_cf,2. The periodicity of the pattern of color filters 60 may depend on the location within the layer. The periodicity may also differ for the different colors.

In another embodiment according to the invention, the color filters 60 comprise liquid crystal cells. Preferably the electrically controllable liquid crystal cells (according to well known control techniques in the art) enabling a dynamic Moire effect. Normally a viewer has to reposition relative to the Moire effect luminance device 1 in order to see a change in the Moire pattern. Advantageously, the viewer observes a dynamic Moire pattern - even without repositioning himself- in accordance with the electrical control of the liquid crystal cells.

Although the invention has been elucidated with reference to the embodiments described above, it will be evident that alternative embodiments may be used to achieve the same objective. The scope of the invention is therefore not limited to the embodiments described above, but can also be applied to any other applications where a Moire effect is desired such as, for example, traffic signs.

Claims

CLAIMS:

1. A Moire effect lumination device (1) comprising: a housing (10) with an optically transparent window (11), the housing comprising a light source (30), and a grid (20) with a periodicity λ_g arranged in optical relationship with the transparent window (11), characterized in that the light source (30) comprises an array of light emitting elements (31) with a periodicity λ_ls.

2. A Moire effect lumination device (1) according to claim 1, wherein the light emitting elements (31) are chosen to emit light with at least two spectra.

3. A Moire effect lumination device (1) according to claim 2, wherein the light emitting elements (31) are arranged in at least a first array (41) emitting light with a first spectrum and having a periodicity λ_1Sjl and at least a second array (42) emitting light with a second spectrum and having a periodicity λ_ls,₂.

4. A Moire effect lamination device (1) according to any of the proceeding claims where in the periodicities λ_ls or λ_g depend on the location of the array of light emitting elements (31) and the grid (20), respectively.

5. A Moire effect lumination device (1) according to any of the preceding claims, wherein the grid (20) is provided with optical lenses (50) having a periodicity X₁.

6. A Moire effect lumination device (1) according to any of the preceding claims, wherein the light emitting elements (31) are LEDs.

7. A Moire effect lumination device (1) according to any of the preceding claims, wherein the grid is provided with color filters (60).

8. A Moire effect lumination device (1) according to claim 7, wherein the color filters comprise at least a first set of color filters (61) having a first optical filtering characteristic and a periodicity X_c^₁ and at least a second set of color filters (62) having a second optical filtering characteristic and a periodicity λcf_j2.

9. A Moire effect lumination device (1) according to claims 7 or 8, wherein the color filters (60) comprise liquid crystal cells.

10. A Moire effect lumination device (1) according to claim 9, wherein the liquid crystal cells are arranged to be controllable enabling a dynamic Moire effect.

11. A method to create a Moire pattern comprising the steps: Providing a light source (30)

Providing a grid (20) with a periodicity λ_g arranged in optical relationship to the light source, characterized in that the light source (30) comprises an array of light emitting elements (31) with a periodicity λ_ls.

12. A method to create a Moire pattern according to claim 11, wherein the light emitting elements (31) are chosen to emit light with at least two spectra.

13. A method to create a Moire pattern according to claim 12, wherein the light emitting elements (31) are arranged in at least a first array (41) emitting light with a first spectrum and having a periodicity λ_1Sjl and in at least a second array (42) emitting light with a second spectrum and having a periodicity λ_1Sj2.

14. A method to create a Moire pattern according to claim 13, wherein the grid (20) is provided with optical lenses (50).

15. A method to create a Moire pattern according to the claims 11 to 14, wherein the light emitting elements (31) are LEDs.

16. A method to create a Moire pattern according to claims 11 to 15, wherein the grid is provided with color filters (60).

17. A method to create a Moire pattern according to claim 16, wherein the grid is provided with at least a first set of color filters (61) having a first optical filtering characteristic and a periodicity X_c^₁ and at least a second set of color filters (62) having a second optical filtering characteristic and a periodicity λcf_j2.

18. A method to create a Moire pattern according to claims 16 or 17, wherein the color filters (60) comprise liquid crystal cells.

19. A method to create a Moire pattern according to claim 18, wherein the liquid crystal cells are controlled to enable a dynamic Moire effect.