WO2006040716A1

WO2006040716A1 - Light modulator

Info

Publication number: WO2006040716A1
Application number: PCT/IB2005/053297
Authority: WO
Inventors: Mark T. Johnson; Peter A. Duine
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-10-15
Filing date: 2005-10-07
Publication date: 2006-04-20
Also published as: TW200627040A

Abstract

For the light modulator (1) for modulating light to have a light modulating element (2) being able to have a different list of attainable optical states for modulating the light, the light modulator (1) has a light modulating element (2) and a medium controller. Furthermore, the light modulating element (2) has a medium (5) comprising a fluid, and an optical state depending on a physical state of the medium (5). Furthermore, the medium controller is arranged to enable an at least partly non-laminar flow in the medium (5) associated with a predetermined optical state for modulating the light.

Description

Light modulator

The invention relates to a light modulator for modulating light.

The invention also relates to a device comprising such a light modulator.

A light modulator for modulating light is disclosed in US 6,144,361. The disclosed light modulator is a transmissive electrophoretic display. The display comprises a regular lateral array of transmissive electrophoretic light modulating elements; each uniformly illuminated from the rear by a backlight. Each light modulating element is comprised of a suspension of charged, black or colored light-absorbing pigment particles in a light-transmissive fluid. Each light modulating element is also comprised of a light- transmissive front and rear window, at least one non-obstructing counter electrode, and at least one non-obstructing, vertically-disposed collecting electrode. With the application of appropriate potentials to the collecting and counter electrodes, each light modulating element can be switched between a light and dark state. In the dark state, the light-absorbing pigment particles are distributed to cover the horizontal area of the light modulating element, thus absorbing light from the backlight and preventing it from reaching the viewer. In the light state, the light- absorbing pigment particles are collected on vertical surfaces within the light modulating element, thus allowing light from the backlight to pass through the light modulating element and reach the viewer. As a result, each light modulating element has a list of attainable optical states for modulating the light, the number of attainable optical states in the list being relatively low.

It is an object of the invention to provide a light modulator of the kind mentioned in the opening paragraph which has a light modulating element being able to have a different list of attainable optical states for modulating the light.

To achieve this object, the invention provides a light modulator for modulating light comprising a light modulating element and a medium controller,

- the light modulating element having - a medium comprising a fluid, and

- an optical state depending on a physical state of the medium, the medium controller being arranged to enable an at least partly non- laminar flow in the medium associated with a predetermined optical state for modulating the light. As a consequence of the at least partly non-laminar flow in the medium the physical state of the medium differs from the physical state resulting from a laminar flow in the medium. Therefore, the light modulating element is able to attain optical states different from optical states relating to only laminar flow. This is in contrast to the light modulating element disclosed in US 6,144,361, where the optical states relate to only laminar flow. In an embodiment the medium comprises an additional fluid, and the medium controller comprises an additional fluid controller being arranged to enable a movement of the additional fluid for achieving the at least partly non-laminar flow in the medium. Then the flow in the medium is being induced by the movement of the additional fluid relative to the fluid, e.g. applicable using the principle of electrowetting. In another embodiment the medium comprises particles in the fluid, and the medium controller comprises a particle controller being arranged to enable a movement of the particles for achieving the at least partly non- laminar flow in the medium. Then the flow in the medium is being induced by the movement of the particles through the fluid, e.g. applicable using the principle of electrophoresis. The non-laminar flow may comprise (traveling) vortices like e.g. a von

Karman vortex street. Then the flow varies with time in a regular, cyclic fashion. As a result the attainable optical states are relatively well controllable. If the non-laminar flow comprises a turbulent flow, the flow is irregular and many complex flow shapes are possible, e.g. cloud shapes, snakes, swirls, stars, water flow and rough water effects, resulting in an increased number of attainable optical states. If, furthermore, the turbulent flow comprises a convection flow, the flow shapes are less irregular and the attainable optical states are relatively well controllable.

In another embodiment the optical state depends on a local density of the fluid. These local density variations are being induced by e.g. the movement of the additional fluid through the fluid or the movement of the particles through the fluid. As a local density variation results in a relatively small variation of the optical state, only smooth patterns inside the optical element appear if, furthermore, the particles or the additional fluid are substantially non-contributing to the optical state. In another embodiment the optical state depends on a position of the additional fluid or on a position of the particles.

In another embodiment the fluid is substantially non-contributing to the optical state. Then the optical states depend solely on the position of the additional fluid or the particles which position can relatively accurately be determined. As a result relatively accurate optical states can be obtained.

In another embodiment the medium comprises a further fluid contributing to the optical state, the further fluid being different from the fluid. Then the number of attainable optical states is increased. If, furthermore, the fluid is a liquid and the further fluid is a gas, gas bubbles in the liquid can be generated resulting in a further increased number of attainable optical states.

If each particle comprises a net magnetic moment, the ability of the particles to be moved can relatively easily be tuned and the particle controller may comprise a switchable magnet, e.g. a solenoid, which can easily be manufactured. If each particle comprises a net charge, the ability of the particles to be moved can relatively easily be tuned. In a variation on the embodiment the particle controller comprises electrodes for receiving potentials and drive means being arranged for controlling the potentials. Such kind of particle controller can easily be manufactured. If the electrodes and drive means are able to generate electric fields for enabling the movement of the particles to have components in three independent directions, detailed 3D patterns inside the optical element can be generated. The movement in three independent directions can be generated by both 2D and 3D electric fields. If the light modulating element has a viewing surface for being viewed by a viewer, the electrodes have substantially flat surfaces facing the particles and the surfaces are substantially parallel to the viewing surface, then the geometry of the electrodes can be relatively simply manufactured. If, furthermore, the surfaces of the electrodes are present in a substantially flat plane, the manufacturing process of the electrodes is further simplified and the movement of the particles has an in-plane component.

Each particle may even comprise both a net charge and a net magnetic moment. It is also possible that the particles become magnetized or electrically polarized during operation by the presence of the applied magnetic or electric fields. An example of the latter case is a dielectrophoretic system, where polarized particles move along directions of varying field strength under the influence of an applied AC electric field.

In another embodiment the light modulating element comprises a reservoir portion substantially non-contributing to the optical state and an optical active portion substantially contributing to the optical state. Then the particles in the reservoir are hidden from the viewer. If, furthermore, the movement of the particles comprises a reset-movement of the particles into the reservoir portion, and subsequently a picture-movement of the particles for achieving the at least partly non- laminar flow in the medium, then the accuracy of the attainable optical states is improved.

In another embodiment the particle controller is further arranged to enable a movement of the particles for achieving a laminar flow in the medium. Then the light modulating element is able to have attainable optical states relating to both laminar and at least partly non-laminar flow and, as a result, the light modulating element is able to have a relatively large number of attainable optical states for modulating the light.

In another embodiment the medium comprises further particles and still further particles, the particles, the further particles and the still further particles having mutually dissimilar optical properties, and the particle controller is further arranged to enable a movement of the particles, the further particles and the still further particles for achieving an at least partly non- laminar flow in the medium. Then the light modulating element is able to have a relatively large number of attainable optical states for modulating the light. If, furthermore, the particles, the further particles and the still further particles are cyan, magenta and yellow (which absorb red, green and blue light, respectively), respectively, a full brightness full-color system may be realized. If the light modulator further comprises a light source for illuminating the light modulating element, the light modulator modulates light from a light source for e.g. lighting applications, e.g. a lighting system for lighting a room or a road which has a light output which is adjustable in intensity and/or color and/or direction. Furthermore, the possibly smooth and detailed patterns inside the optical element can be made more visible and may even be projected.

Another aspect of the invention provides an electrophoretic display panel for displaying a picture comprising the light modulator as claimed in claim 3. In an embodiment, the light modulating element comprises a pixel, and the particle controller is arranged to enable a movement of the particles for achieving an at least partly non- laminar flow in the medium. In a variation on the embodiment, the display panel is an active matrix display panel. Electrophoretic display panels can form the basis of a variety of applications where information may be displayed, for example in the form of information signs, public transport signs, advertising posters, pricing labels, billboards etc. In addition, they may be used where a changing non-information surface is required, such as wallpaper with a changing pattern or colour, especially if the surface requires a paper like appearance.

Another aspect of the invention provides a display device comprising the display panel as claimed in claim 24 and a circuitry to provide image information to the display panel.

The mere fact that certain measures are mentioned in different claims does not indicate that a combination of these measures cannot be used to advantage.

These and other aspects of the display panel of the invention will be further elucidated and described with reference to the drawings, in which:

Figure 1 shows diagrammatically a front view of an embodiment of the display panel;

Figure 2 shows diagrammatically a cross-sectional view along II-II in Figure 1;

Figure 3 shows diagrammatically a cross-sectional view along III-III in Figure

2;

Figure 4 shows diagrammatically a first flow shape in the plane II-II;

Figure 5 shows diagrammatically a second flow shape in the plane II-II; Figure 6 shows diagrammatically a third flow shape in the plane II-II;

Figure 7 shows diagrammatically a fourth flow shape in the plane II-II;

Figure 8 shows examples of patterns created by applying various potential pulses to a first electrophoretic sample, with wide central electrode;

Figure 9 shows examples of patterns created by applying various potential pulses to a first electrophoretic sample, with narrow central electrode;

Figure 10 shows a full colored stacked electrophoretic light modulator to create a complex full colored image from a simple electrode structure;

Figure lla shows a schematic cross-section with no voltage applied;

Figure 1 Ib shows a schematic cross-section with a dc-voltage applied; Figure l ie shows a top view photograph demonstrating the continuous oil film;

Figure 1 Id shows a top view photograph demonstrating oil retraction, and Figure 12 shows an element of an LED based pixelated lamp, where the complex image resulting from a small sized light modulating element is projected onto a surface.

In all the Figures corresponding parts are referenced to by the same reference numerals.

Figures 1-3 show an example of the display panel 1 having a first substrate 8, a second transparent opposed substrate 9 and a plurality of light modulating elements 2, being pixels 2. Preferably, the pixels 2 are arranged along substantially straight lines in a two-dimensional structure. Other arrangements of the pixels 2 are alternatively possible, e.g. a honeycomb arrangement. In an active matrix embodiment, the pixels 2 may further comprise switching electronics, for example, thin film transistors (TFTs), diodes, MIM devices or the like.

The pixel 2 has an electrophoretic medium 5. The electrophoretic medium 5, having charged particles 6 in a transparent fluid, is present between the substrates 8,9. Electrophoretic media 5 are known per se from e.g. US 2002/0180688. The particles 6 and the fluid have dissimilar optical properties. The particles 6 may have any color, whereas the fluid may have any color different from the color of the particles 6. Examples of the color of the particles 6 are for instance red, green, blue, yellow, cyan, magenta, white or black. The particles 6 may be large enough to scatter light, or small enough to substantially not scatter light. The pixel 2 has a viewing surface 91 for being viewed by a viewer.

Furthermore, the barriers 514 forming pixel walls separate the pixel 2 from its environment. The optical state of the pixel 2 depends on a physical state of the medium, e.g. the position of the particles 6.

In transmissive mode, the optical state of the pixel 2 is determined by the portion of the visible spectrum incident on the pixel 2 at the side 92 of the first substrate 8 that survives the cumulative effect of traversing through the first substrate 8, medium 5 and the second substrate 9. In reflective mode, the optical state of the pixel 2 is determined by the portion of the visible spectrum incident on the pixel 2 at the side of the second substrate 9 that survives the cumulative effect of traversing through the second substrate 9, medium 5, subsequently interacting with surface 15 of the first substrate 8 which may be reflective or have any color and subsequently traversing back through medium 5 and the second substrate 9.

If the fluid is substantially non-contributing to the optical state of the pixel 2, the amount and color of the light transmitted by medium 5 is controlled by the position and color of the particles 6. When the particles 6 are positioned in the path of the light that enters the pixel 2, the particles 6 absorb or scatter a selected portion of the light and the remaining light is transmitted. When the particles 6 are substantially removed from the path of the light entering the pixel 2, the light can pass through the pixel 2 and emerge without significant visible change. The light seen by the viewer, therefore, depends on the distribution of particles 6 in the pixel 2.

The medium controller is arranged to enable an at least partly non-laminar flow in the medium associated with a predetermined optical state for modulating the light. The medium controller has a particle controller being arranged to enable a movement of the particles 6 for achieving the at least partly non- laminar flow in the medium 5. Furthermore, the particle controller is further arranged to enable a movement of the particles 6 for achieving a laminar flow in the medium 5. The particle controller has electrodes 10,11 for receiving potentials and drive means 100 being arranged for controlling the potentials. In this case, each one of the electrodes 10,11 has a substantially flat surface 110,111 facing the particles 6. Furthermore, in this layout the electrodes 10,11 are arranged to enable the particles 6 to move in a plane parallel to the viewing surface 91.

In an example, consider the particles 6 to be positively charged and black. Furthermore, the fluid is transparent. Consider the pixel layout of Figures 2 and 3 and the display panel being used in light transmissive mode. The optical state of the pixel 2 is determined by the portion of the visible spectrum incident on the pixel 2 at the entrance window 92 that survives the cumulative effect of traversing through the first substrate 8, medium 5 and the second substrate 9 and exits through viewing surface 91. Consider white light e.g. generated by a (back)light source (not drawn), incident on the entrance window 92. By appropriately changing the potentials received by the electrodes 10,11, the particles 6 are being moved through the fluid. This movement of the particles 6 induces the at least partly non-laminar flow in the medium. The non-laminar flow may comprise convection (Figure 4), a vortex (see Figure 5) or travelling vortices like e.g. a von Karman vortex street (see Figure 6), or turbulent flow (see Figure 7). The appearance of the different flow shapes depends among others on the dimensions of the pixel 2, the size of and distance between the electrodes 10,11, the value, form (i.e. pulse shape) and duration of the applied potentials, the charge, size and surface properties of the particles 6 and the viscosity of the medium 5. In the third dimension different non-laminar flow patterns are possible, and these have been visualized in experiments that have been performed. In these experiments it has been observed that under certain conditions the particles 6 do not move smoothly, hi particular, for particles 6 which move in the plane parallel to the viewing surface 91 (using in-plane electric fields), it is apparent that turbulent flow and convection flow of particles 6 takes place. The complex shapes which are thus formed (cloud shapes, snakes, swirls, stars, water flow and rough water effects) are reproducible and, by adjusting the driving potentials, are tunable.

Some examples of patterns which have been produced in an electrophoretic display panel 1 are shown in Figures 8 and 9. The display panel 1 has particles 6 able to be moved in a liquid, which is encapsulated between two glass plates 8,9 and surrounded by a pixel wall structure. These patterns are produced by applying different potentials to only a single set of electrodes (a central electrode 11 and a connected set of side electrodes 10) that are arranged in a plane parallel to the viewing surface 91. The particles 6 move under the influence of the applied electric fields, and primarily in a direction in the plane parallel to the viewing surface 91. Note that whilst many patterns can be created - varying from a simple, uniform pattern at lower potentials, to the highly complex patterns created by the turbulent flow effects at higher potentials - the patterns in each of the individual pixels are almost identical and are reproducible.

In some cases, the complex patterns are the result of collisions of sets of particles 6 moving from two separate electrodes. By introducing additional electrodes, even more variable patterns can be realised by allowing more sets of particles 6 to collide together. Whilst the examples of Figures 8 and 9 represent a light modulator with black particles 6 in a transparent liquid, it is clear that in preferred embodiments the attractiveness of the light modulating element will be enhanced by introducing colours to the light modulator. This can be achieved by introducing either coloured particles, coloured liquids coloured light sources or colour filters to the light modulator. For example, by having a light modulator with white particles 6 in a blue liquid a cloud effect can be achieved. Such a light modulator can be placed upon the ceiling of either a room or a corridor or alternatively inside the roof of a car or other mode of transport, to provide the user with the impression of being outdoors. In such a light modulator, the brightness of the light modulator should ideally far exceed 1000Cd/m2, and could be realised using a bright backlight array (10,000 Cd/m2) with a highly transmissive light modulating element.

In another embodiment, the light modulator is illuminated with a limited, but adjustable set of colors created by adjusting the color of the light source. This can be achieved by creating either a lighting system with multiple colored light sources (such as an array of LED lighting or a set of spot lights of various colors) or by using a light whose color can be adjusted by changing its color temperature (e.g. by changing the applied potential to the lamp). In either case, the color of the entire light modulator can be adjusted, or alternatively a color gradient can be created across the light modulator, by locally adjusting the color of the light sources. In this manner, it is possible to display an impression of e.g. several different weather types, sunsets etc.

Figure 10 shows a full colored stacked electrophoretic light modulator to create a complex full colored image from a simple electrode structure. This embodiment is able to realise a full colour complex image in an electrophoretic light modulator. The light modulator has a stacked system of simple electrophoretic display panels in which the particles move in the plane of the substrates (using in-plane electric fields) — see Figure 10. Whilst any combination of coloured particles could be combined in this manner - also in combination with one or more coloured liquid or colour filter - the preferred embodiment incorporates stacked layers with cyan, magenta and yellow particles 6,60,600 (which absorb red, green and blue light respectively). In this case, a full brightness full colour light modulator - with any area being made any colour - is realised. The full colour complex shapes which are thus formed can be made more complex by mixing the individual shapes in each layer. As an example the effect of an open fire is created, where flame like shapes are created by suitably shaped red, yellow and blue effects. Again, these shapes are reproducible and, by adjusting the driving potentials, tuneable.

It has been observed that it is possible to move particles 6 in three dimensions, either by using the convectional fluid flows created under higher potentials using the simple in-plane electrode structures of Figures 2 and 3, or by adding additional electrodes on the second substrate 9. In this manner, detailed 3D images can be created from a limited number of electrodes. These images can then be illuminated using e.g. a LED or spotlight, which scatter from the particles 6 in case these are made scattering. In this manner, an electronic candle effect is realized.

As the size of the images (typically < lmm) may be too small for a large light modulator application, it is proposed to create a light modulating element with considerably higher cell gap, cell gap being the distance between the first and the second substrate 8,9. A cell gap of around lmm- lcm is sufficient to create images of around 10cm lateral dimension, as may be required in a large light modulator application. As the size of the patterns are clearly limited by the presence of the pixel wall structures, the spacing between the pixel wall structures have to be sufficiently large, or the pixel walls may even be removed. In this case, it is advantageous to introduce a reset or pre-conditioning sequence between subsequent images (or image sequences) to ensure that the particles 6 are in a well defined starting position (e.g. fairly uniformly distributed across the light modulating element) before the new images are introduced. In another embodiment the medium comprises an additional fluid 50, and the medium controller comprises an additional fluid controller being arranged to enable a movement of the additional fluid 50 for achieving the at least partly non- laminar flow in the medium 5. An example is an electro-wetting system. In this system an electric field is used to move a liquid 50 across a surface. Figures 1 Ia-I Ib show the schematic cross-section with no voltage applied (see Figure 1 Ia), therefore a homogeneous oil film 50 is present or a dc- voltage applied (Figure 1 Ib), causing the oil film to contract. The top view photographs Figures lie and Hd demonstrate the continuous oil film and corresponding oil retraction obtained with a homogeneous electrode, respectively. In equilibrium the oil 50 naturally forms a stable and continuous film between the water 51 and the hydrophobic insulator 52. However, when a potential difference is applied across the hydrophobic insulator 52 an electrostatic term is added to the energy balance and the stacked state is no longer energetically favorable. The system can lower its energy by moving the water into contact with the insulator 52, thereby displacing the oil 50 (Figure 1 Ib) and exposing the underlying white surface. The balance between electrostatic and capillary forces determines how far the oil 50 is moved to the side.

Electro-wetting can provide an optical switch with a high reflectivity (>40%) and contrast (>15). In addition to the attractive optical properties, the principle exhibits a video-rate response speed (~10 ms), is capable of achieving a high-brightness color display panel and is readily scalable from a pixel size of 160 micron up to several cm (larger pixels switch more slowly as the liquid film must travel a greater distance).

By appropriately changing the potentials received between the transparent electrode 53 and the water 51, the water 51 is being moved through the oil 50. This movement of the water 51 induces the at least partly non-laminar flow in the medium 5. The non- laminar flow may comprise convection (see Figure 4), a vortex (see Figure 5) or travelling vortices like e.g. a von Karman vortex street (see Figure 6), or turbulent flow (see Figure 7). A color light modulating element can be achieved by e.g. adding a dye to the water 51.

The light modulator can be used in direct view and projection applications. As the size of the images of displays (typically < lmm) is too small for a large lighting application, a light modulator can be created with considerably larger pixels of several centimeter lateral dimension. In addition, the size of the patterns are clearly limited by the presence of the pixel wall structures in e.g. electro-wetting displays. These can be made significantly further separated, or removed.

In a further embodiment a pixelated lamp is considered whereby an array of collimated LED can be individually turned on. In this embodiment (see Figure 12), this will be used to project an image through the detailed image created by the light modulating element onto a surface, hi this manner, a small (around lmm) light modulating element can be realized to create a far larger complex image.

Claims

CLAIMS:

1. A light modulator (1) for modulating light comprising a light modulating element (2) and a medium controller, the light modulating element (2) having

- a medium (5) comprising a fluid, and - an optical state depending on a physical state of the medium (5), the medium controller being arranged to enable an at least partly non- laminar flow in the medium (5) associated with a predetermined optical state for modulating the light.

2. A light modulator (1) as claimed in claim 1 characterized in that the medium (5) comprises an additional fluid (50), and the medium controller comprises an additional fluid controller being arranged to enable a movement of the additional fluid (50) for achieving the at least partly non-laminar flow in the medium (5).

3. A light modulator (1) as claimed in claim 1 characterized in that the medium comprises particles (6) in the fluid, and the medium controller comprises a particle controller being arranged to enable a movement of the particles (6) for achieving the at least partly non- laminar flow in the medium (5).

4. A light modulator (1) as claimed in claim 1 characterized in that the non- laminar flow comprises a turbulent flow.

5. A light modulator (1) as claimed in claim 4 characterized in that the turbulent flow comprises a convection flow.

6. A light modulator (1) as claimed in claim 1 characterized in that the optical state depends on a local density of the fluid.

7. A light modulator (1) as claimed in claim 2 or 3 characterized in that the optical state depends on a position of the additional fluid (50) or on a position of the particles (6).

8. A light modulator (1) as claimed in claim 2 or 3 characterized in that the particles (6) or the additional fluid (50) are substantially non-contributing to the optical state.

9. A light modulator (1) as claimed in claim 2 or 3 characterized in that the fluid is substantially non-contributing to the optical state.

10. A light modulator (1) as claimed in claim 1 characterized in that the medium

(5) comprises a further fluid contributing to the optical state, the further fluid being different from the fluid.

11. A light modulator (1) as claimed in claim 10 characterized in that the fluid is a liquid and the further fluid is a gas.

12. A light modulator (1) as claimed in claim 3 characterized in that each particle

(6) comprises a net magnetic moment.

13. A light modulator (1) as claimed in claim 3 characterized in that each particle (6) comprises a net charge.

14. A light modulator (1) as claimed in claim 13 characterized in that the particle controller comprises electrodes (10,11) for receiving potentials and drive means (100) being arranged for controlling the potentials.

15. A light modulator (1) as claimed in claim 14 characterized in that the electrodes (10,11) and drive means (100) are able to generate electric fields for enabling the movement of the particles (6) to have components in three independent directions.

16. A light modulator (1) as claimed in claim 14 characterized in that the light modulating element (2) has a viewing surface (91) for being viewed by a viewer, the electrodes (10,11) have substantially flat surfaces (110,111) facing the particles (6) and the surfaces (110,111) are substantially parallel to the viewing surface (91).

17. A light modulator (1) as claimed in claim 16 characterized in that the surfaces (110,111) of the electrodes (10,11) are present in a substantially flat plane.

18. A light modulator (1) as claimed in claim 3 characterized in that the light modulating element (2) comprises a reservoir portion substantially non-contributing to the optical state and an optical active portion substantially contributing to the optical state.

19. A light modulator (1) as claimed in claim 18 characterized in that the movement of the particles (6) comprises a reset-movement of the particles (6) into the reservoir portion, and subsequently a picture-movement of the particles (6) for achieving the at least partly non- laminar flow in the medium (5).

20. A light modulator (1) as claimed in claim 3 characterized in that the particle controller is further arranged to enable a movement of the particles (6) for achieving a laminar flow in the medium (5).

21. A light modulator (1) as claimed in claim 3 characterized in that the medium

(5) comprises further particles (60) and still further particles (600), the particles (6), the further particles (60) and the still further particles (600) having mutually dissimilar optical properties, and the particle controller is further arranged to enable a movement of the particles (6), the further particles (60) and the still further particles (600) for achieving an at least partly non-laminar flow in the medium (5).

22. A light modulator (1) as claimed in claim 1 characterized in that the light modulator (1) further comprises a light source for illuminating the light modulating element (2).

23. A light modulator (1) as claimed in claim 22 characterized in that the modulated light is being projected.

24. An electrophoretic display panel (1) for displaying a picture comprising the light modulator (1) as claimed in claim 3.

25. A display device comprising the display panel (1) as claimed in claim 24 and a circuitry to provide image information to the display panel (1).