Patent Publication Number: US-2009219488-A1

Title: Diode or Laser Light Source Illumination Systems

Description:
FIELD OF THE INVENTION 
     The present invention relates to diode or laser light source illumination systems, and more particularly to an illumination system having red, green and blue diode and/or laser light sources. 
     BACKGROUND OF THE INVENTION 
     Light emitting diodes (LED) are commonly used as a light source for an image projecting apparatus or projector, because of its properties of reduced power consumption and heat release, decreased dimensions, and extended lifetime. 
     In the field of liquid crystal projectors, a liquid crystal projector has been proposed in Japanese Patent Laid-Open Publication No. 2002-244211. In the liquid crystal projector, a liquid crystal panel has to be illuminated with linear polarization, and for the proposed projection device there are three LED array light sources corresponding to light sources of red, green, and blue, which are arranged so as have the diode light outputs being directed through three corresponding polarized light converting elements into a dichroic prism, where the resulting light beam being output from the prism is directed to a liquid crystal panel via a polarizing beam splitter, and the light beam is then reflected from the liquid crystal panel through the polarizing beam splitter via a projection lens enabling a projection of the light beams modulated on the liquid crystal panel onto a screen. 
     Thus, the image projection device described in Japanese Patent Laid-Open Publication No. 2002-244211 uses a single liquid crystal panel arranged together with a polarizing beam splitter in order to direct the modulated light beam through the projection lens. However, the arrangement of the liquid crystal panel and the polarizing beam splitter results in a displayed image, which may appear fuzzy and lacking in contrast. 
     Thus, there is a need for an image projection device, which can be produced at a small size and still maintain a high quality image projection. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide one or more illumination systems, which can be used in order to produce an image projection device, which may have a small size and still provide a high quality image. 
     According to a first aspect of the invention, there is provided an illumination system comprising:
         at least three diode and/or laser light sources including a red, a green and a blue light source,   at least three polarizing light converting elements corresponding to each colour of light sources,   at least three liquid crystal panels corresponding to each colour of light sources, and   at least one prism arrangement,   wherein red light is directed through a first polarizing light element and a first liquid crystal panel into a first side of the prism arrangement, green light is directed through a second polarizing light element and a second liquid crystal panel into a second side of the prism arrangement, and blue light is directed through a third polarizing light element and a third liquid crystal panel into a third side of the prism arrangement, and   wherein the prism arrangement is adapted to reflect or emit the polarized light received at the first, second and third prism sides in a single direction throughout a fourth side being an exit plane of the prism.       

     According to a preferred embodiment of the first aspect of the invention, the illumination system further comprises a projection lens with the prism arrangement being adapted to reflect or emit the polarized light received at the first, second and third prism sides in a single direction throughout the fourth side of the prism and through the projection lens. Here, it is preferred that the optical distance from each of the liquid crystal panels to the projection lens is substantially equal. 
     For the first aspect of the invention it is preferred that the prism arrangement comprises a dichroic prism or a cross dichroic prism. 
     Preferably, the liquid crystal panel is arranged parallel to the first prism side, the second liquid crystal panel is arranged parallel to the second prism side, and the third liquid crystal panel is arranged parallel to the third prism side. 
     For the first aspect of the invention it is also preferred that the first polarizing light element is arranged parallel to the first liquid crystal panel, the second polarizing light element is arranged parallel to the second liquid crystal panel, and the third polarizing light element is arranged parallel to third liquid crystal panel. 
     It is further preferred that the light sources are arranged so that the resulting light is directed substantially perpendicular to the corresponding polarizing light element. 
     Several solutions for the light sources may be used according to the first aspect of the present invention. Here, one or more or each light source may be a single light emitting diode or an array of light emitting diodes, with each array holding a plurality of light emitting diodes of similar colour. It is also within an embodiment of the first aspect of the invention that one or more or each light source comprises a laser or a laser diode. The first aspect of the invention also covers an embodiment wherein one or more of the light sources comprise a combination of a light emitting diode or an array of light emitting diodes and a laser diode or laser. 
     It is also within an embodiment of the first aspect of the invention that the illumination system further comprises circuitry for controlling each liquid crystal panel as a function of an image or video input signal, whereby the polarized light received at the first, second and third prism sides represents three colour modulated versions of the same image, said three image versions being modulated by polarized red, green and blue light, respectively. Here, the first, second and third liquid crystal panels may be arranged or aligned relatively to each other so that the light reflected by the prism throughout the exit plane of the prism represents a colour image being a combination of the received three colour modulated image versions. 
     It is also preferred that the illumination system of the first aspect of the invention further comprises power supply circuitry for supplying power to each light source. Here, the power supply circuitry may be adapted for an individual control or adjustment of the power delivered to the light sources. 
     According to a second aspect of the present invention there is provided a light source module comprising:
         at least a first diode or laser light source providing light in the visible range,   at least a second light source comprising an UV (ultra-violet) or a low wavelength blue diode or laser light source, and   a beam splitter or reflection system,   wherein the beam splitter or reflection system is arranged to emit light received from the first light source and light received from the second light source. It is preferred that the first light source providing visible light comprises a single colour diode or laser light source. Here, the colour provided by the single colour diode or laser light source may be selected from the group consisting of: red, green, blue and white colours.       

     It is within a preferred embodiment of the second aspect of the invention that the light source providing visible light is a blue diode light source providing blue diode light. 
     For the embodiments of the present invention having a module or system with a low wavelength blue light source such as a low wavelength blue diode or laser light source, it is meant that when a module or system has another light source providing blue light, then the wavelength of the low wavelength blue light source is lower than the wavelength of the other blue light source. As an example, the low wavelength blue light source may have a wavelength in the range of 410-455 nm while the other blue light source may have a wavelength above 460 nm such as about 468 nm. If the module or system having a low wavelength blue light source does not have another light source providing blue light, then it is preferred that the low wavelength blue light source has a wavelength in the range of 410-455 nm. 
     Also for the second aspect of the invention several solutions for the light sources may be used. Here, one or more light sources may be a single light emitting diode or an array of light emitting diodes, with each array holding a plurality of light emitting diodes of similar colour. It is also within an embodiment of the second aspect of the invention that one or more light sources comprise a laser or a laser diode. The second aspect of the invention also covers an embodiment wherein one or more of the light sources comprise a combination of a light emitting diode or an array of light emitting diodes and a laser diode or laser. 
     According to an embodiment of the second aspect of the invention the beam splitter or reflection system is arranged to emit light received from the first light source and light received from the second light source in a direction throughout a single exit plane of the beam splitter or reflection system. 
     It is also within an embodiment of the second aspect of the invention that the light from the first and second light sources received by the beam splitter or reflection system is emitted from the beam splitter or reflection system in a single direction or along a single optical axis. 
     The second aspect of the invention also covers an embodiment, wherein the light source module further comprises a polarizing light element, and wherein the light from the first and second light sources emitted by the beam splitter or reflection system is directed through said polarizing light element. 
     The second aspect of the invention also covers an embodiment, wherein the light source module further comprises a liquid crystal panel, and wherein the light from the first and second light sources being emitted by the beam splitter or reflection system is directed through said liquid crystal panel. 
     The second aspect of the invention also covers an embodiment, wherein the light source module further comprises a polarizing light element and a liquid crystal panel, wherein the light from the first and second light sources being emitted by the beam splitter or reflection system is directed through the polarizing light element and the liquid crystal panel. 
     It is within an embodiment of the second aspect of the invention that the polarizing light element and/or the liquid crystal panel are/is arranged parallel to the exit plane of the beam splitter or reflection system. 
     It is also within an embodiment of the second aspect of the invention that the light source module further comprises a projection lens or lens system, and wherein the light being directed through the liquid crystal panel is further directed through the projection lens or lens system. 
     It is also within an embodiment of the second aspect of the invention that the light source module further comprises power supply circuitry for supplying power to each light source. Here, the power supply circuitry may be adapted for an individual control or adjustment of the power delivered to the diode light sources. 
     According to a third aspect of the invention there is provided an illumination system comprising:
         a plurality of diode and/or laser light modules, and   a prism arrangement surrounded by the plurality of light modules and arranged so as to emit a combination of lights received from the plurality of light modules, wherein at least one of said plurality of light modules is a UV (ultra-violet) or low wavelength blue light module comprising a first light source having a UV or low wavelength blue diode or laser light source. Here, the UV or low wavelength blue light module may further comprise a second visible diode or laser light source, and a beam splitter or a reflection system, wherein the beam splitter or reflection system is arranged to emit light received from the first and second light sources. It is preferred that the beam splitter or reflection system is arranged to emit light received from the first and second light sources in a direction throughout a single exit plane of the beam splitter or reflection system. The second visible light source may be a blue diode or laser light source or a green diode light source, but in a preferred embodiment the second light source is a blue diode light source.       

     It is within an embodiment of the third aspect of the invention that the prism arrangement comprises a cubical prism. It is also within an embodiment of the third aspect of the invention that the prism arrangement comprises a dichroic prism or a cross dichroic prism. 
     It is within a preferred embodiment of the third aspect of the invention that the prism has a first side, a second side, a third side and a fourth side, and that the plurality of light modules comprises three modules with a first module emitting light into the first side of the prism, a second module emitting light into the second side of the prism, and a third module emitting light into the third side of the prism. Here, it is preferred that the prism arrangement is adapted to emit the combination of lights received at the first, second and third prism sides in a single direction throughout the fourth side of the prism. 
     According to an embodiment of the third aspect of the invention the plurality of light modules may further comprise a red light module with a red diode and/or laser light source and a green light module with a green diode light source. Here, the first light module may be the red light module, the second light module may be the green light module and the third light module may be the UV or low wavelength blue light module. 
     The third aspect of the invention also covers an embodiment, wherein each light module comprises a corresponding polarizing light element. Here, it is preferred that for each light module the emitted light is directed through the corresponding polarizing light element and into the prism arrangement. 
     It is also within an embodiment of the third aspect of the invention that each light module comprises a corresponding liquid crystal panel. Here, it is preferred that for each light module the emitted light is directed through the corresponding polarizing light element and the corresponding liquid crystal panel and into the prism arrangement. It is also within an embodiment of the third aspect of the invention that each polarizing light element and/or each liquid crystal plane are/is arranged parallel to a corresponding side of the prism arrangement. 
     The third aspect of the invention also covers embodiments wherein the light modules do not comprise a corresponding liquid crystal panel. But here, a liquid crystal panel or element may be arranged on a light outgoing side of the prism arrangement. 
     The third aspect of the invention also covers embodiments, wherein the illumination system further comprises a Digital Light Processing unit, which Digital Light Processing Unit may be arranged on a light outgoing side of the prism arrangement. In one embodiment, wherein the Digital Light Processing unit may be a 3-chip Digital Light Processing unit, an optical lens and a second prism may further be arranged on the light outgoing side of the prism arrangement so that the outgoing light from the prism arrangement is directed through the optical lens and reflected by the second prism as light input to the Digital Light Processing unit. The illumination system may further comprise a projections lens or outgoing lens system, and the second prism and the Digital Light Processing unit may be arranged so and so that light output from the Digital Light Processing unit is transmitted through the second prism and directed through the projection lens or outgoing lens system. In an alternative embodiment, wherein the Digital Light Processing unit may be a 1-chip Digital Light Processing unit, a condensing lens, a colour filter and a shaping lens may further be arranged on the light outgoing side of the prism arrangement so that the outgoing light from the prism arrangement is directed through the condensing lens, the colour filter and the shaping filter on to the surface of the Digital Light Processing unit. Also for this alternative embodiment, the illumination system may further comprise a projection lens or outgoing lens system, and the light output from the Digital Light Processing unit may be directed through the projection lens or outgoing lens system. 
     It is within an embodiment of the third aspect of the invention that the illumination system further comprises a projection lens or lens system, and wherein the light being emitted from the prism arrangement is further directed through said projection lens or lens system. Here, it is preferred that when the illumination system comprises several liquid crystal panels, then the optical distance from each of the liquid crystal panels to the projection lens is substantially equal. 
     According to an embodiment of the third aspect of the invention, the UV or low wavelength blue light source may comprise a UV light emitting diode. 
     Also for the third aspect of the invention several solutions for light sources of the light modules may be used. Here, one or more light sources of the light modules may be a single light emitting diode or an array of light emitting diodes, with each array holding a plurality of light emitting diodes of similar colour. It is also within an embodiment of the third aspect of the invention that one or more light sources of the light modules comprise a laser or a laser diode. The third aspect of the invention also covers an embodiment wherein one or more of the light sources of the light modules comprise a combination of a light emitting diode or an array of light emitting diodes and a laser diode or laser. Thus, one or more of the light source modules may comprise an array of light emitting diodes, with each array holding a plurality of light emitting diodes of similar colour. It is also within an embodiment of the third aspect of the invention that part of or each of the light source modules comprises a laser or a laser diode. 
     For embodiments of the third aspect of the invention wherein each diode light module comprises a corresponding polarizing light element and a corresponding liquid crystal panel, it is preferred that the illumination system further comprises circuitry for controlling each liquid crystal panel as a function of an image or video input signal, whereby the polarized light received by the prism arrangement represents three colour modulated versions of the same image. Here, the illumination system may have a first, second and third liquid crystal panel, which are arranged or aligned relatively to each other so that the light emitted by the prism arrangement represents a colour image being a combination of the received three colour modulated image versions. 
     It is also within an embodiment of the third aspect of the invention that the illumination system further comprises power supply circuitry for supplying power to each light modules, said power supply circuitry being adapted for an individual control or adjustment of the power delivered to the light modules. 
     According to a fourth aspect of the invention there is provided a projection illumination system comprising:
         a plurality of projection modules, each said projecting module comprising one or more diode and/or laser light sources and one or more light modulating units and a projection lens or lens assembly, each said light modulating unit comprising a liquid crystal panel or a Digital Light Processing unit,   wherein, for each projection module, the light sources, the light modulating unit(s) and the projection lens are arranged for projecting modulated light through the projection lens, and   wherein the projection lenses are arranged for projecting the modulated light on a single projection screen.       

     For illumination systems according to the fourth aspect of the invention wherein one or more light modulating units comprise a liquid crystal panel, it is preferred that each of the projecting modules further comprises at least one polarizing light element. 
     It is within an embodiment of the fourth aspect of the invention that for each liquid crystal panel, there is one or more corresponding polarizing light elements, said polarizing light element(s) being arranged in the optical path(s) between the liquid crystal panel and the light source(s) having light modulated by said liquid crystal panel. 
     The fourth aspect of the invention also covers an embodiment, wherein the light sources include one or more UV (ultra-violet) or low wavelength blue light sources. 
     For the system of the fourth aspect of the invention it is preferred that the system comprises at least two projection modules, such as two or three projection modules. 
     According to an embodiment of the fourth aspect of the invention, then at least one of the projection modules may further comprise a prism arrangement arranged for having three different light sources emitting light into three corresponding sides of the prism, said prism arrangement being adapted to emit the combination of lights received at said three prism sides in a single direction throughout at fourth side of the prism and through the projection lens of the projection module. 
     The fourth aspect of the invention also covers embodiments, wherein at least one of the projection modules having a prism arrangement is a DLP projection module with a light modulating unit having a Digital Light Processing unit. The Digital Light Processing Unit may be arranged on a light outgoing side of the prism arrangement. In one embodiment, wherein the Digital Light Processing unit may be a 3-chip Digital Light Processing unit, an optical lens and a second prism may further be arranged on the light outgoing side of the prism arrangement so that the outgoing light from the prism arrangement is directed through the optical lens and reflected by the second prism as light input to the Digital Light Processing unit. The second prism and the Digital Light Processing unit may be arranged so that light output from the Digital Light Processing unit is transmitted through the second prism and directed through the projection lens. In an alternative embodiment, wherein the Digital Light Processing unit may be a 1-chip Digital Light Processing unit, a condensing lens, a colour filter and a shaping lens may further be arranged on the light outgoing side of the prism arrangement so that the outgoing light from the prism arrangement is directed through the condensing lens, the colour filter and the shaping filter on to the surface of the Digital Light Processing unit, and the light output from the Digital Light Processing unit may be directed through the projection lens. 
     It is also within an embodiment of the fourth aspect of the invention that for a projection module having the prism arrangement, a liquid crystal panel may be arranged in the optical path between the fourth side of the prism and the projection lens. Here, a polarizing light element may be arranged in the optical path between the fourth side of the prism and the liquid crystal panel. Alternatively, then for each of the three light sources a polarizing light element may be arranged in the optical path between the light source and the corresponding side of the prism. 
     It is within an embodiment of the fourth aspect of the invention that the prism arrangement comprises a cubical prism. It is also within an embodiment of the fourth aspect of the invention that the prism arrangement comprises a dichroic prism or a cross dichroic prism. 
     According to an embodiment of the system of the fourth aspect of the invention, wherein a projection module has the prism arrangement, then for each of the three light sources a polarizing light element may be arranged in the optical path between the light source and the corresponding side of the prism, and a liquid crystal panel may be arranged in the optical path between the polarizing light element and the corresponding side of the prism. Here, it is preferred that for a projection module having the prism arrangement arranged for having three different light sources emitting light into three corresponding sides of the prism through the three liquid crystal panels, the optical distance from each of the liquid crystal panels to the projection lens is substantially equal. 
     According to an embodiment of the system of the fourth aspect of the invention, wherein a projection module has the prism arrangement, the three different light sources may include a red, a green and a blue light source. 
     The system of the fourth aspect of the invention also covers an embodiment, wherein a projection module has the prism arrangement, and wherein one of the three different light sources includes a UV (ultra violet) or low wavelength blue light source. Here, one of the three different light sources may be a combined light source having both a first UV or low wavelength blue light source and a second light source for providing light in the visible range. 
     It is within one or more embodiments of the system of the fourth aspect of the invention that at least one of the projection modules comprises a combined light source having both a first UV or low wavelength blue light source and a second light source for providing light in the visible range. It is preferred that for the combined light source, the visible light source is a blue or green light source. 
     For a system according to an embodiment of the fourth aspect of the invention having a projection module comprising the combined diode light source, then the combined light source may comprise a beam splitter or reflection system, said beam splitter or reflection system being adapted for emitting light received from the first and second light sources along a single optical direction thereby providing the light output of the combined light source. Here, for a projection module having a combined light source, a polarizing light element may be arranged in the optical path between the beam splitter or the reflection system and the projection lens, and a liquid crystal panel may be arranged in the optical path between the polarizing light element and the projection lens. 
     According to one or more embodiments of the fourth aspect of the invention, then at least one of the projection modules may comprise a single colour diode light source for providing light in the visible range. Here, the visible diode light source may be a blue or green diode light source. For a projection module having a single colour diode light source, then a polarizing light element may be arranged in the optical path between the diode light source and the projection lens, and a liquid crystal panel may be arranged in the optical path between the polarizing light element and the projection lens. 
     Also for the fourth aspect of the invention several solutions for light sources of the projection modules may be used. Here, one or more light sources of a projection module may be a single light emitting diode or an array of light emitting diodes, with each array holding a plurality of light emitting diodes of similar colour. It is also within an embodiment of the fourth aspect of the invention that one or more light sources of a projection module comprise a laser or a laser diode. The fourth aspect of the invention also covers an embodiment wherein one or more of the light sources of a module comprise a combination of a light emitting diode or an array of light emitting diodes and a laser diode or laser. It is within an embodiment of the fourth aspect of the invention that the light sources include a red, a green and a blue light source. It is also within an embodiment of the fourth aspect of the invention that the light sources include two blue and/or two green light sources. Here, it is preferred that the light sources include at least two blue light sources which may be diode light sources. 
     For a system according to an embodiment of the fourth aspect of the invention having a projection module comprising a UV light source, then it is preferred that the UV light source is a UV light emitting diode. 
     It is within an embodiment of the system of the fourth aspect of the invention, that the optical distance from the liquid crystal panel(s) of a projection module to the corresponding projection lens is substantially equal for all projection modules. 
     In order to optical align the projection modules of a system of the fourth aspect of the invention, then it is preferred that that for at least one of the projection modules, the position of the projection lens can be adjusted in relation to the position of the liquid crystal panel(s). According to an embodiment of the fourth aspect of the invention then the system may comprise three projection modules arranged in a row, and wherein for at least the two outermost arranged projection modules, the position of the projection lens can be adjusted in relation to the position of the liquid crystal panel(s). 
     It is also within an embodiment of the system of the fourth aspect of the invention that the position of at least one of the projection modules can be adjusted in relation to the remaining projection modules. 
     Also for the systems of the fourth aspect of the invention it is preferred that the illumination system further comprises circuitry for controlling each liquid crystal panel as a function of an image or video input signal, whereby the light or polarized light received by the projection lenses represents colour modulated versions of the same image. 
     It is also within an embodiment of the fourth aspect of the invention that the illumination system further comprises power supply circuitry for supplying power to each diode light source. Here, the power supply circuitry may be adapted for an individual control or adjustment of the power delivered to the diode light source. 
     The invention will be further described in the following with the aid of the accompanying drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1   a  and  1   b  are plan views schematically showing illumination systems according to a first and a second embodiment of the first aspect of the present invention, 
         FIG. 2  is a schematic diagram of the illumination system of  FIG. 1  further including circuitry for controlling modulation of liquid crystal panels and circuitry for supplying power to diode light sources according to an embodiment of the present invention, 
         FIG. 3  is a schematic diagram showing the layout of a light emitting diode array according to an embodiment of the present invention, 
         FIG. 4  is a schematic diagram illustrating the arrangement of a projection lens according to an embodiment of the first aspect of the present invention, 
         FIG. 5  is a schematic diagram illustrating the power supply circuitry used for supplying power to the diode light sources according to an embodiment of the present invention, 
         FIG. 6   a  is a plan vies schematically showing a UV light source module according to an embodiment of the second aspect of the invention, 
         FIG. 6   b  is a plan view schematically showing an illumination system according to a first embodiment of the third aspect of the invention, 
         FIG. 6   c  is a plan view schematically showing an illumination system according to a second embodiment of the third aspect of the invention, 
         FIG. 6   d  is a plan view schematically showing an illumination system according to a third embodiment of the third aspect of the invention, 
         FIG. 6   e  is a plan view schematically showing an illumination system according to a fourth embodiment of the third aspect of the invention, 
         FIG. 6   f  is a plan view schematically showing an illumination system according to a fifth embodiment of the third aspect of the invention, 
         FIG. 7  is a plan view schematically showing an illumination system according to a sixth embodiment of the third aspect of the invention, 
         FIG. 8   a  is a plan view schematically showing a projection illumination system according to a first embodiment of the fourth aspect of the invention, 
         FIG. 8   b  is a plan view schematically showing a projection illumination system according to a second embodiment of the fourth aspect of the invention, 
         FIG. 9   a  is a plan view schematically showing a projection illumination system according to a third embodiment of the fourth aspect of the invention, 
         FIG. 9   b  is a plan view schematically showing a projection illumination system according to a fourth embodiment of the fourth aspect of the invention, 
         FIG. 10  is a plan view schematically showing a projection illumination system according to a fifth embodiment of the fourth aspect of the invention, 
         FIG. 11  is a plan view schematically showing a projection illumination system according to a sixth embodiment of the fourth aspect of the invention, 
         FIG. 12  is a plan view schematically showing a projection illumination system according to a seventh embodiment of the fourth aspect of the invention, 
         FIG. 13  is a plan view schematically showing a projection illumination system according to an eight embodiment of the fourth aspect of the invention, 
         FIG. 14  is a plan view schematically showing a projection illumination system according to a ninth embodiment of the fourth aspect of the invention, 
         FIG. 15  is a plan view schematically illustrating optical alignment of a projection illumination system according to the first embodiment of the fourth aspect of the invention, 
         FIG. 16  is a front view schematically illustrating a first embodiment of movement directions of projection lenses used for the optical alignment of the projection illumination system shown in  FIG. 15 , and 
         FIG. 17  is a front view schematically illustrating a second embodiment of movement-directions of projection lenses used for the optical alignment of the projection illumination system shown in  FIG. 15 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A first embodiment of an illumination system according to the first aspect present invention using diode light sources is illustrated in  FIG. 1   a . Here, three light emitting diode (LED) arrays  101   a - 103   a  are arranged as diode light sources, where the first array  101   a  has diodes giving the colour red, the second array  102   a  has diodes giving the colour green, and the third array  103   a  has diodes giving the colour blue. In front of each LED array  101   a - 103   a  is arranged a polarizing filter  104 - 106 , with each polarizing filter being arranged in front of or attached to a liquid circuit display (LCD)  107 - 109 . The three LCD&#39;s,  107 - 109 , are arranged on three sides of a cross dichroic prism  110 , with a projection lens  111  being arranged in front of a fourth side of the prism  110 . The prism  110  combines the three colour images modulated by the three LCD&#39;s  107 - 109 , to form a colour image being projected by the lens  111 . In  FIG. 1   a  is also shown a projection screen  112  on which the image is being projected. 
     A second embodiment of an illumination system according to the first aspect of the present invention using light sources is illustrated in  FIG. 1   b . The system of  FIG. 1   b  is similar to the system of illustrated in  FIG. 1   a  with the exception that the in  FIG. 1   b  the light sources are single light emitting diodes, single lasers or laser diodes,  101   b - 103   b . The remaining components of the system of  FIG. 1   b  are similar to the components of  FIG. 1   a  and therefore the same numerals are used for these components in  FIG. 1   a  and  FIG. 1   b.    
       FIG. 2  includes the illumination system of  FIG. 1   b , but further includes circuitry  210  for controlling image modulation of the LCD&#39;s  107 - 109  and circuitry  211  for supplying power to the diode light sources  101   b - 103   b.    
     Light Emitting Diodes 
     Example using Light Emitting Diode Arrays 
     In  FIG. 3  is shown the layout of a light emitting diode array  301 , which may be used in the embodiment illustrated in  FIG. 1   a . The diode array  301  contains 9 LED&#39;s  302  and 9 resistors  303 . Three diode arrays  301  are used for the system of  FIG. 1   a , a red colour array  101   a , a green colour array  102   a , and a blue colour array  103   a.    
     According to an embodiment of the invention, the following LED units have been used for the arrays: 
     Array  101   a : Ultrahelle tiefrote SMD-LED 0603, 45 mcd, 120°,
 
Array  102   a : Ultrahelle grúne SMD-LED 0603, 65 mcd, 120°,
 
Array  103   a : Ultrahelle blau SMD-LED 0603, 60 mcd, 120°,
 
     Here, SMD-LED 0603 is the LED product number, xx mcd (millicandel) is the brightness/amount of light generated by the LED, and 120° is the angle in which the light from the LED is distributed. 
     For an embodiment of the invention, the current through the LED&#39;s may be non adjustable, and for these LED arrays the following resistors may be used: 
     Array  101   a: ,  ¼ Watt, 76.50 Ohm
 
Array  102   a:  0805, ⅛ Watt, 107 Ohm
 
Array  103   a:  0805, ¼ Watt, 107 Ohm
 
     Example Using Single LED Diodes 
     A number of single LED diodes may be used instead of LED arrays. This is illustrated in the embodiment of  FIG. 1   b . Here, one red LED unit, one green LED unit, and one blue LED unit are used. According to an embodiment of the invention, the following single diode LED units have been used: 
     Diode  101   b : Luxeon® Star/O red, 1 Watt, 810.000 mcd, 10°
 
Diode  102   b : Luxeon® Star/O green, 1 Watt, 600.000 mcd, 10°
 
Diode  103   b : Luxeon® Star/O blue, 1 Watt, 200.000 mcd, 10°
 
     Here, xx mcd is the amount of light generated by the LED, and 10° is the angle in which the light from the LED is distributed. 
     Laser Light Sources 
     The present invention also covers embodiments wherein part of or all of the light sources are laser light sources. Laser light sources may be used to obtain a higher light output power when compared to the light output delivered by light emitting diodes. 
     A laser is a device that controls the way that energized atoms release photons. “Laser” is an acronym for light amplification by stimulated emission of radiation, which describes very succinctly how a laser works. 
     In the following are some typical lasers and their emission wavelengths: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Laser Type 
                 Wavelength (nm) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Argon fluoride (UV) 
                 193 
               
               
                   
                 Krypton fluoride (UV) 
                 248 
               
               
                   
                 Xenon chloride (UV) 
                 308 
               
               
                   
                 Nitrogen (UV) 
                 337 
               
               
                   
                 Argon (blue) 
                 488 
               
               
                   
                 Argon (green) 
                 514 
               
               
                   
                 Helium neon (green) 
                 543 
               
               
                   
                 Helium neon (red) 
                 633 
               
               
                   
                 Rhodamine 6G dye (tunable) 
                 570-650 
               
               
                   
                 Ruby (CrAlO3) (red) 
                 694 
               
               
                   
                 Nd: Yag (NIR) 
                 1064 
               
               
                   
                 Carbon dioxide (FIR) 
                 10600 
               
               
                   
                   
               
            
           
         
       
     
     Laser medium can be a solid, gas, liquid or semiconductor. Lasers are commonly designated by the type of lasing material employed:
         Solid-state lasers have lasing material distributed in a solid matrix (such as the ruby or neodymium:yttrium-aluminum garnet “Yag” lasers). The neodymium-Yag laser emits infrared light at 1,064 nanometers (nm). A nanometer is 1×10-9 meters.   Gas lasers (helium and helium-neon, HeNe, are the most common gas lasers) have a primary output of visible red light. CO2 lasers emit energy in the farinfrared, and are used for cutting hard materials.   Excimer lasers (the name is derived from the terms excited and dimers) use reactive gases, such as chlorine and fluorine, mixed with inert gases such as argon, krypton or xenon. When electrically stimulated, a pseudo molecule (dimer) is produced. When lased, the dimer produces light in the ultraviolet range.   Dye lasers use complex organic dyes, such as rhodamine  6 G, in liquid solution or suspension as lasing media. They are tunable over a broad range of wavelengths.   Semiconductor lasers, also referred to as laser diodes. These electronic devices are generally very small and use low power. They may be built into larger arrays, such as the writing source in some laser printers or CD players.       

     For the systems of the present invention, then when the total size of the illumination systems or light modules has to be taken into account, then laser diodes are preferred as light source when compared to other laser types. Semiconductor laser diodes covering wavelengths within the visible range are commercially available and supplied by a great number of manufactures. 
     Polarizing Filters 
     The purpose of polarizing filters  104 - 106  is to control light from the LED arrays  101   a - 103   a  into the LCD&#39;s  107 - 109 . If an electrical charge is applied to an LCD, the LCD untwist, thereby changing the angel of light passing through. However, this change is not visible by the human eye unless a polarizing filter is applied in front of the LCD. This means that the polarizing filters  104 - 106  are necessary for making the light changes within the LCD&#39;s  107 - 109  visible for the human eyes. 
     The wavelength λ of the blue SMD-LED 0603 is 468 nm. Consequently, the following polarizing filter from CVI Laser Optics can be applied: TFP-527-PW-1025-UV. The polarizing filter “TFP-527-PW-1025-UV” has a transmission efficiency of 95% for λ&gt;=527 nm. However, due to the dimensions of this particular filter type, it may be necessary to resize the polarizing filter glass into the size needed in the apparatus. 
     The wavelength λ of the green SMD-LED 0603 is 520 nm. Consequently, the following polarizing filter can be applied: ColorPol® VIS500BC3. The ColorPol® VIS500BC3 polarizer has a Transmission Efficiency of 72% for A=520 nm with contrast &gt;1000:1 
     The wavelength λ of the red SMD-LED 0603 is 660 nm. Consequently, the same polarizing filter can be used as for the green LED array. For the red LED array the ColorPol® VIS500BC3 polarizer has a Transmission Efficiency of 83% for λ=660 nm with contrast &gt;1000:1 
     Liquid Crystal Displays 
     The three LCD&#39;s  107 - 109  in  FIGS. 1   a  and  1   b  are each being controlled by a corresponding video or image to LCD decoder or converters being part of the circuitry  210  in  FIG. 2 . There is one decoder or converter for each of the colours red, green and blue. The video or image to LCD decoders are standard decoders or converters for converting for example video, mpg, RGB of DVI input signals. 
     LCD Positioning 
     For the illumination system of  FIGS. 1   a  or  1   b  to achieve an ultimate high quality displayed picture/image with high sharpness and contrast, then the three LCD&#39;s  107 - 109 , which preferably are attached to the prism  110 , should be fine tuned in position, so that all three colours of light entering the LCD&#39;s and exiting the projection lens  112  come together substantially exactly on top of each other on, for example, a white wall or canvas. All parts of the system of  FIGS. 1   a  or  1   b  should preferably be assembled and fine tuned in position when leaving the production assembling line. However, fine tuning of the system can all so be achieved manually. 
     The LCD&#39;s  107 - 109  can be attached to the prism  110  by means of a material such as miniature screws or glue. 
     Prism 
     The prism  110  of  FIGS. 1   a  and  1   b  may be a dichroic prism designed to fit to the LDC&#39;s used for the illumination system. In  FIG. 1   a  the diode arrays  101   a  and  103   a  are arranged parallel and opposite to each other with the diode light of these arrays entering the prism  110  at a direction being substantially perpendicular to the exit plane of the prism, while the diode array  102   a  is arranged opposite to the exit plane of the prism, whereby the diode light of the array  102   a  is entering the prism at a direction being substantially equal to the light output direction. 
     The dichroics prism  110  may be customised to fit the size of various illumination systems. The dichroic prism can be formed by combining four triangular poles also named “right angle prisms” to create one rectangular solid prism. High precision is required in the processing and adhesion of poles to avoid dark lines and double images caused by misaligned discrete dichroic surfaces. In addition, the dichroic prism  110  may be coated according to the wavelengths of the diode light sources  101 - 103 , to thereby act as a beam-splitter. When using 0.1 inch LCD&#39;s the side lengths of the prism  110  should be at least 0.1 inch each. 
     Example 
     The blue LED array  103   a  in the above described diode array example has a wavelength of 468 nm. Thus, the dichroic prism  110  may be coated to reflect substantially all the blue diode light (coming from the blue entry side of the prism  110 ) on to the optical axis within a wavelength range of 390-494 nm. However. if ultra violet, UV, light is applied to the system in combination with the blue diode light, as discussed in accordance with the system illustrated in  FIG. 6   b , then the diachronic prism  110  may be coated to reflect light of wavelengths in the range of 240-494 nm. 
     The red LED array  101   a  has a wavelength of 660 nm. Thus, the dichroic prism  110  may be coated to reflect substantially all red diode light (coming from the red entry side of the prism  110 ) on to the optical axis within a wavelength range of 591-685 nm. 
     The green LED  102   a  array has a wavelength of 520 nm. Here, it is important that the red and blue diode light is not interfering with the green diode light, and the prism  110  should be coated to transmit substantially all the green diode light within a wavelength range of 495-590 nm. 
     Projection Lens 
       FIG. 4  is a schematic diagram illustrating the arrangement of a projection lens  111  according to an example of the present invention. It should be noted that according to an embodiment of the illumination system of the present invention, it is preferred to use an achromatic lens for the projection lens  111 . 
     Achromatic Lenses: 
     Achromatic lenses are superior to singlets lenses for infinite conjugate distances and large apertures. Consequently, it may be an obvious choice for improving the apparatus to use an achromatic lens. 
     An achromatic lens consists of two optical components cemented together, usually a positive low-index (crown) element and a negative high-index (flint) element. The additional design freedom provided by using doublets lenses allows for further optimization of performance not possible with singlets lenses. Therefore, achromatic lenses may have noticeable advantages over simple lenses. Achromatic lenses may be far superior to simple lenses for multi-colour (“white light”) imaging. The two elements composing an achromatic lens (literally, “a lens with no colour”) are paired together for their ability to correct the colour separation inherent in glass. Having eliminated the problematic chromatic aberrations, achromatic lenses may become the most cost-efficient means for good polychromatic illumination and imaging. 
     Freedom from spherical aberration and coma implies better on-axis performance at larger apertures. Unlike simple lenses, achromatic lenses may provide consistently smaller spot sizes and superior images without decreasing the clear aperture. Because on-axis achromatic performance will not deteriorate with larger clear apertures, “closing down” the optical system becomes unnecessary. 
     The example illustrated in  FIG. 4  is based on the following: 
     To find the right projection lens with the correct specifications, it may necessary to make calculations with regards to the dimensions of the apparatus and the expected screen size. In  FIG. 4  is shown the optical axis and the distance S from the LCD  108  at the back of the prism  110  to the projection lens  111  and the distance S′ from the lens  111  to a projection screen/canvas or wall  112 . 
     To calculate the type and size of projection lens for the apparatus the following calculation formulas may be used: 
       Magnification Equation:  M=S′/S  or  Y=M*X    
       Thin Lens Equation: 1 /S+ 1 /S′= 1 /f    
     M=magnification
 
S′=distance from projection lens to Screen/canvas or white wall
 
S=distance from the LCD to the Projection lens.
 
f=focal length
 
x=Size of LCD
 
Y=Size of screen
 
     Calculations: 
     In this example of the illumination system there is used 0.1″ LCD&#39;s. The desired size of the projected picture is around 10″. The distance from the projection lens  111  to a wall or canvas  112  is 100 cm. 
     Thus the following is given: S=1 cm; S′=100 cm; X=0.1″; Y=10″ 
         M=S′/S=&gt;M= 1000 mm/10 mm=&gt; M= 100 
       1 /S+ 1 /S′= 1 /f=&gt; 1/10 mm−1/1000 mm=1 /f=&gt;f= 1/0.1001=&gt;f=9.99=&gt;f&gt;&gt;10 mm 
     Consequently, the following visible Achromatic Doublets lens available from Thorlabs Inc may be used: 
     Part nr. AC080-010-A1, focal length (f)=efl:10.00 mm, DIA: 8.0 mm, Material: BAFN10-SFL6 
     LED Power Supply 
       FIG. 5  is a schematic diagram illustrating the power supply circuitry used for supplying power to the diode light sources according to an embodiment of the present invention. 
     In  FIG. 5 , each LED or LED array, D 1  (red), D 2  (green), D 3  (blue) is powered by a supply circuit comprising a variable resistor R 1 , a fixed resistor R 2 , a transistor T 1 , and a voltage source U. The power delivered to a diode light source D 1 , D 2 , D 3  may be manually adjusted bye means of R 1 . The power to the light sources D 1 , D 2 , D 3  may also or alternatively be adjusted automatically, which may be achieved bye implementing feedback from a photo-detector. 
     If a voltage of 3.5 V is needed to drive a diode light source D 1 , D 2 , D 3  then a supply voltage source U of at least 5 V should be provided. The resistor R 1  may be variable in the range of for example 10K Ohm to 35 K Ohm. The value of resistor R 2  may be 40 Ohm, while the transistor T 1  may have an amplification factor β of about 100. The current of the red diode D 1  may be adjusted in the range of 10-30 mA, while the current of green diode D 2  and blue diode D 3  may be adjusted in the range 10-20 mA. It is preferred that the red diode D 1  has a nominal current of 30 mA, while the green diode D 2  and the blue diode D 3  both have a nominal current of 20 mA. 
     Use of Ultra Violet or Low Wavelength Blue Light Source 
     In order to improve the light output of an illumination system, such as the systems according to the first aspect of the invention, then according to the second, third and fourth aspects of the invention, a UV light source or a low wavelength blue light source may be added. Thus, the UV light or low wavelength blue light may be combined with the visible light colours blue, green, red or white. Using UV light or low wavelength blue as an additional light source may improve the picture quality of the displayed image and also result in a higher light output of the illumination system. Ultra violet light is normally not visible to the human eye. Thus, for the UV light to become visible to the human eye, a light beam projected from an illumination system having a light source combination including a UV light source should be displayed on a special surface such as for example a white canvas coated with a substance such as optical white etc. Standard white Xerox paper can also be used as canvas, for example Xerox paper in the size 3A attached to a wall. However, the selected canvas should preferably have the ability to reflect the UV light. In addition, to enjoy the picture improvements added by the use of UV light, the light level in the physical room and surroundings should be lowered to a minimum. Using standard white Xerox paper as canvas may reflect UV light projected by a projecting illumination system, resulting in a sharper picture and higher brightness. The UV light source in the projecting illumination system may generate a rainbow blue colour, which in combination with a blue colour light source may deliver a higher blue colour level in a projected picture. The colour blue, in general, is the most difficult colour to be transmitted through filters and optics in a projecting illumination system. Therefore, it is important to have as much blue colour as possible. Together with an adjusted level of the colour red and green light source, white light may be achieved and used as means for projecting a picture/image. 
     Examples of UV Light Emitting Diodes: 
     To prevent UV light from damaging the human eye, UV LED&#39;s with a long wavelength may be used, for example UV light with a wavelength of 390-400 nm or 400-410 nm. In addition, the longer the UV light wavelength is, the more rainbow blue colour from the UV light is gained. Since a high level of rainbow blue colour from the UV light is desirable, the following UV light wavelengths may be used: 390-400 nm or 400-410 nm. Using a wavelength in the area of 400-410 nm makes it possible to use standard beam splitters made of glass, thus keeping the price of the beam splitter at a low level. Beam splitters with wavelengths in the range of 240-390 nm are much more expensive compared to standard beam splitters made of glass. 
     According to preferred embodiments of the present invention, the following UV-LED units may be used: 
       113 : Ledtronics part nr. 100CUV395-12D, wavelength 390-400 nm
   113 : Ledtronics part nr. L200CUV405-12D, wavelength 400-410 nm
 
     Low Wavelength Blue Light Sources: 
     For the embodiments of the present invention having a module or system with a low wavelength blue light source such as a low wavelength blue diode or laser light source, it is meant that when a module or system has another light source providing blue light, then the wavelength of the low wavelength blue light source is lower than the wavelength of the other blue light source. As an example, the low wavelength blue light source may have a wavelength in the range of 410-455 nm while the other blue light source may have a wavelength above 460 nm such as about 468 nm. If the module or system having a low wavelength blue light source does not have another light source providing blue light, then it is preferred that the low wavelength blue light source has a wavelength in the range of 410-455 nm. For systems or modules having a low wavelength blue light source together with a light source of a higher wavelength then a beam splitter may be used which reflects light in the range of 410-455 nm, while trans-mitting light of a higher wavelength such as 468 nm. 
     Description of Illumination Systems Using UV or Low Wavelength Blue Light Sources 
       FIG. 6   a  shows a light source module having a UV or low wavelength blue light source according to an embodiment of the second aspect of the invention. The light source module of  FIG. 6   a  uses two light sources with different wavelengths. However, part of the components used for the module of  FIG. 6   a  may be similar to the components used for the system described in  FIGS. 1   a  and  1   b , and therefore the same numerals are used for these components. 
     The module of  FIG. 6   a  comprises a single colour diode light source  103 , a beam splitter  114  coated to reflect UV light or low wavelength blue light, a UV or low wavelength blue light source  113 , a polarizing filter  104 , a liquid crystal display LCD  109 , and a projection lens  111 . To add ultra violet or low wavelength blue light to the module, a beam splitter  114  is used. The purpose of the beam splitter  114  is to combine two incident and perpendicular light beams. The beam splitter  114  may be coated to reflect UV light in the wavelength range of 240-410 nm or to reflect low wavelength blue light in the wavelength range of 410-455 nm. UV or low wavelength blue light from the light source  113  is directed into the beam splitter  114 , which reflects the UV or low wavelength blue light onto the optical axis of the outgoing light. Light from the other light source  103  is directed through the beam splitter in the direction of the optical axis. The light thus reflected or transmitted into the direction of the optical axis then continues entering the polarizing filter  104  into the LCD  109  and then through the projection lens  111 . The colours blue, green, red and white may be selected so that they do not contain the same wavelength as the UV or low wavelength blue light, and it is therefore possible to have a beam splitter allowing light of these colours to pass through the beam splitter. In a preferred embodiment the single colour diode light source  103  is a blue colour diode light source, and it may be an array of light emitting diodes or a single light emitting diode or laser diode. 
     Several types of beam splitters  114  may be used in a UV or low wavelength blue light source module in order to reflect or transmit UV or low wavelength blue light:
         A first type can be a “long wavelength transmitting beam splitter”, transmitting long wavelengths, such as the light from a blue diode light source  103 , and reflecting short wavelengths, such as light from a UV or low wavelength blue light source  113 . This situation is illustrated in  FIG. 6   a.      A second type can be a “short wavelength transmitting beam splitter”, transmitting short wavelengths and reflecting longer wavelength. Here, light from the UV or low wavelength blue light source  113  is transmitted through the beam splitter, while light from the blue diode light source  103  is reflected on to the optical axis.       

       FIG. 6   b  shows an illumination system according to a first embodiment of the third aspect of the invention. The system of  FIG. 6   b  is a combination of part of the systems according to the first aspect of the invention illustrated in  FIG. 1   a  or  FIG. 1   b  and part of the UV or low wavelength blue light source module illustrated in  FIG. 6   a . Thus, part of the components used for the system of  FIG. 6   b  may be similar to the components used for the system described in  FIGS. 1   a  or  1   b  and  FIG. 6   a , and therefore the same numerals are used for these components. 
     The system of  FIG. 6   b  corresponds to the systems illustrated in  FIG. 1   a  or  FIG. 1   b , with the exception that the blue diode light source  103   a ,  103   b  has been replaced by a UV or low wavelength blue light source module similar to part of the UV or low wavelength blue light source module of  FIG. 6   a  and comprising a visible blue colour diode light source  103 , which may be a single LED or comprise an array of LED&#39;s, a UV or a low wavelength blue light emitting diode  113  and a beam splitter  114 . Thus, when compared to the system of  FIG. 1   b , then for the system of  FIG. 6   b  a combination of UV or low wavelength blue diode light and a visible, higher wavelength blue diode light enters prism  110  through the polarizing filter  104  and the corresponding LCD  109 . 
     For the system in  FIG. 6   b , the beam splitter  114  may be coated to reflect UV light with a wavelength between 240-410 nm or to reflect low wavelength blue light in the wavelength range of 410-455 nm. UV or low wavelength blue light  113  is directed into the beam splitter  114 , which reflects the UV or low wavelength blue light on to the optical axis. Higher wavelength blue light from a blue LED array/laser diode  103  is directed through the beam splitter  114 . The higher wavelength blue light may have a wavelength about 468 nm, thus allowing the blue light to pass through the beam splitter. The higher wavelength blue light and UV or low wavelength blue light emitted from the beam splitter then continues entering the polarizing filter  104  into the LCD  109  and dichroic prism  110  and exiting through the projection lens  111 , with the image being projected on the screen or canvas  112 . 
     For the system of  FIG. 6   b , the dichroic prism  110  may be coated to reflect the red colour light coming from diode  101  with a wavelength of 591-685 nm. Since UV light has a wavelength of 240-410 nm, the dichroic prism  110  cannot reflect the UV light on to the optical axis if the UV light enters from the red entry side. The prism  110  is further coated so that the green colour light coming for diode  102  with a wavelength of 520 nm is transmitted through the dichroic prism  110 . Also here, UV light with a wavelength between 240-410 nm cannot be transmitted through the green light entry side of the prism  110 . 
       FIG. 6   c  shows an illumination system according to a second embodiment of the third aspect of the invention. The system of  FIG. 6   c  corresponds to the system of  FIG. 6   b , but in  FIG. 6   c  the LCD&#39;s  107 ,  108  and  109  are omitted. Instead a common LCD  108  is arranged between the prism  110  and the lens system  115 . For the system of  FIG. 6   c , LED arrays are used instead of the single diodes of  FIG. 6   b , and in  FIG. 6   c  three light emitting diode (LED) arrays  101   a - 103   a  are arranged as diode light sources, where the first array  101   a  has diodes giving the colour red, the second array  102   a  has diodes giving the colour green, and the third array  103   a  has diodes giving the colour blue. In addition, a UV or low wavelength blue light source  113  and beam splitter  114  have been added to the blue entry side of the dichroic prism  110 . The three polarizing filters  104 - 106  are arranged on three sides of the cross dichroic prism  110 . The prism  110  combines the three colour lights. The Illuminating lights from LED arrays and UV or low wavelength blue light source whose luminance distribution is made uniform are modulated through the LCD  108 . The colour lights modulated by the LCD  108  are projected on a screen by a projecting lens optical system  115  so that a projection image whose luminance distribution is satisfactorily made uniform can be obtained. 
     The dichroic prism  110  of  FIG. 6   c  may be coated to reflect substantially all the blue diode light including UV or low wavelength blue light (coming from the blue entry side of the dichroic prism) on to the optical axis within a wavelength range of 240-494 nm. 
       FIG. 6   d  shows an illumination system according to a third embodiment of the third aspect of the invention. The system of  FIG. 6   d  corresponds to the system of  FIG. 6   c , but in  FIG. 6   d  the common LCD  108  of  FIG. 6   c  has been replaced by a liquid crystal light valve  141  and a polarizing beam splitter  131 . In  FIG. 6   d , the LED array light sources  101   a - 103   a  are composed of light emitting diodes corresponding to light sources of red, green, and high wavelength blue, respectively. In addition, a UV or low wavelength blue light source  113  and a beam splitter  114  have been added to the blue entry side of the dichroic prism  110 . The three polarizing filters  104 - 106  are arranged on three sides of a cross dichroic prism  110 . The prism  110  combines the UV or low wavelength blue light and three colour lights and lighten up the liquid crystal light valve  141 . The polarizing beam splitter  131  functions as a polarizer, which makes uniform the polarized lights incident on the liquid crystal light valve and also functions as an analyser for projection lights. The light modulated by the liquid crystal light valve  141  is projected on screen or canvas  112  by a projection lens  111 . 
     Also here, the dichroic prism  110  may be coated to reflect substantially all the blue diode light including UV or low wavelength blue light (coming from the blue entry side of the dichroic prism) on to the optical axis within a wavelength range of 240-494 nm. 
       FIG. 6   e  shows an illumination system according to a fourth embodiment of the third aspect of the invention. The system of  FIG. 6   e  corresponds to the system of  FIG. 6   d , but in  FIG. 6   e  the crystal light valve  141  and the beam splitter  131  have been replaced by an optical lens  171 , a 3-chip Digital Light Processing™ unit  151  and a prism  161 . 
     Also in  FIG. 6   e , the LED array light sources  101   a - 103   a  are composed of light emitting diodes or laser diodes corresponding to light sources of red, green, and high wavelength blue, respectively. In addition, a UV or low wavelength blue light source  113  and a beam splitter  114  have been added to the blue entry side of the dichroic prism  110 . The prism  110  combines the UV or low wavelength blue light and three colour lights and lighten up the 3-chip DLP® unit  151 . The white light generated by the light sources (red, green, high wavelength blue, UV or low wavelength blue combined) passes through the optical lens  171  and the prism  161 , which reflects the light into the 3-chip DLP® unit. The 3-chip DLP® unit contains a colour filtering prism and each DLP® chip comprises a Digital Micromirror Device, DMD. Each DLP® chip is dedicated to one of these three colours; the coloured light, which is reflected by the micromirrors, is then combined and passed through the projection lens  111  to form an image that is projected on screen or canvas  112 . The Digital Light Processing™ technology is marketed by Texas Instruments. 
     Also here, the dichroic prism  110  may be coated to reflect substantially all the blue diode light including -UV or low wavelength blue light (coming from the blue entry side of the dichroic prism) on to the optical axis within a wavelength range of 240-494 nm. 
       FIG. 6   f  shows an illumination system according to a fifth embodiment of the third aspect of the invention. The system of  FIG. 6   f  corresponds to the system of  FIG. 6   e , but in  FIG. 6   f  the 3-chip DLP® 151 of  FIG. 6   e  has been replaced by a 1-chip DLP® 181, while the condensing lens  171  is maintained, and a colour filter (colour wheel)  191  and a shaping lens replaces the prism  161  of  FIG. 6   e.    
     Also in  FIG. 6   f , the LED array light sources  101   a - 103   a  are composed of light emitting diodes or laser diodes corresponding to light sources of red, green, and blue, respectively. In addition, a UV or low wavelength blue light source  113  and a beam splitter  114  have been added to the blue entry side of the dichroic prisme  110 . The prism  110  combines the UV or low wavelength blue light and three colour lights and lighten up the 1-chip DLP®  181 . The white light generated by the light sources (red, green, blue, UV or low wavelength blue combined) passes through a condensing lens  171  and colour wheel filter  191  and shaping lens  172 , causing red, green, and blue light to be shone in sequence on the surface of the Digital Micromirror Device, DMD, of the 1-chip DLP®. The switching of the mirrors within the DMD, and the proportion of time the mirrors are “on” or “off” is coordinated according to the colour shining on them. The light, which is reflected by the micromirrors, is then passed through the projection lens  111  to form an image that is projected on screen or canvas  112 . The human visual system integrates the sequential colour and sees a full-colour image, 
     Also here, the dichroic prism  110  may be coated to reflect substantially all the blue diode light including UV or low wavelength blue light (coming from the blue entry side of the dichroic prism) on to the optical axis within a wavelength range of 240-494 nm. 
       FIG. 7  shows an illumination system according to a sixth embodiment of the third aspect of the invention. The system of  FIG. 7  corresponds to the system of  FIG. 6   b , but in  FIG. 7  the beam splitter  114  has been replaced with reflection mirrors  117 ,  118  and a lens filter lens. The remaining components of the system of  FIG. 7  are similar to the components of  FIG. 6   b  and therefore the same numerals are used for these components in  FIG. 6   b  and  FIG. 7 . In  FIG. 7  is shown an alternative way of adding UV or low wavelength blue light to high wavelength blue diode light by use of the lens filter  116  and the reflection mirrors  117 ,  118  on the blue entry side of prism  110 . Light from the high wavelength blue LED or LED array  103  is directed towards the mirror  118 , which reflects the light beam on to the lens filter  116 . From the lens filter  116  the light beam is emitted into the polarizing filter  104 , the LCD  108  and via the prism  110  on to the optical axis. Light from the UV or low wavelength blue light source  113  is directed into the mirror  11 , which reflects the light beam on to the lens filter  116 . From the lens filter  116  the UV or low wavelength blue light beam is emitted into the polarizing filter  104 , the LCD  109  and via the prism  110  on to the optical axis. 
     The purpose of the lens filter  116  is to filter and redirect the incoming light, reflected by the mirrors  117 ,  118 , on to the optical axis. It is important that the two reflecting mirrors  117 ,  118  are situated and adjusted in angel (above 45° according to incoming light beam) so that the reflected light beams from the mirrors  117 ,  118 , overlap when projected through the optical axis and on to a canvas  112  or screen. When compared to the system of  FIG. 6   b , the solution of  FIG. 7  is a less effective way to implement UV or low wavelength blue light into the prism  110 . The result will be a loss in the amount light emitted from the blue and UV or low wavelength blue light sources  103 ,  113 . Even though this solution is less elegant, the solution can effectively be used when implemented in a system or apparatus with a fixed small picture size (fore example 10″ and with a small distance from the apparatus to the canvas  112 , possible less then 1 meter). 
     It should be understood that for the modules and systems described in connection with  FIGS. 6   a - 6   f  and  FIG. 7 , the light emitting diodes, diode arrays or single LED diodes discussed above for use in the systems of  FIGS. 1   a  and  1   b  may be used. In the same way, the polarizing filters, liquid crystal displays, prism and projection lens discussed above for use in the systems of  FIGS. 1   a  and  1   b  may be used in the systems of  FIGS. 6   a - 6   f  and  FIG. 7 . Also the power supply circuitry an the circuitry for controlling image modulation of the LCD&#39;s illustrated and discussed above in connection with  FIGS. 2 and 5  for use in the systems of  FIG. 1   a  and  1   b  may be used in the systems of  FIGS. 6   a - 6   f  and  FIG. 7 . 
     Description of Projection Illumination Systems Having Several Projection Modules 
       FIG. 8   a  shows a projection illumination system according to a first embodiment of the fourth aspect of the invention. The system of  FIG. 8   a  comprises three projection modules,  800   a ,  800   b ,  800   c , where each module has diode light sources and a projection lens, with the projection lenses being arranged or optical aligned in a row so as to project light on the same projection screen  812 . 
     The module  800   a  corresponds to the system of the first aspect of the invention illustrated in  FIG. 1   a  and the modules  800   b  and  800   c  both correspond to the system of the second aspect of the invention illustrated in  FIG. 6   a . Thus, the components used for module  800   a  are similar to the components used for the system described in  FIG. 1   a  as follows: three light emitting diode (LED) arrays  801   a - 803   a  are arranged as diode light sources, where the first array  801   a  has diodes giving the colour red, the second array  802   a  has diodes giving the colour green, and the third array  803   a  has diodes giving the colour blue. In front of each LED array  801   a - 803   a  is arranged a polarizing filter  804 - 806 , with each polarizing filter being arranged in front of or attached to a liquid circuit display (LCD)  807 - 809 . The three LCD&#39;s,  807 - 809 , are arranged on three sides of a cross dichroic prism  810 , with a projection lens  811  being arranged in front of a fourth side of the prism  810 . The prism  810  combines the three colour images modulated by the three LCD&#39;s  807 - 809 , to form a colour image being projected by the lens  811 . In  FIG. 8   a  is also shown a projection screen  812  on which the image is being projected. 
     The components used for modules  800   b  and  800   c  are similar to the components used for the system described in  FIG. 6   a  and are as follows: a single colour diode light source  822   a  or  823   a , a beam splitter  814  coated to reflect UV or low wavelength blue light, a UV or low wavelength blue light source  813   a , a polarizing filter  824 ,  825 , a liquid crystal display (LCD)  826 ,  827 , and a projection lens  828 ,  829 . To add ultra violet or low wavelength blue light to the module, the beam splitter  814  is used. The discussion given above for UV or low wavelength blue light emitting diodes and in connection with the beam splitter  114  of  FIG. 6   a  is naturally also valid for the UV or low wavelength blue light source and the beam splitter  814  of modules  800   b ,  800   c . In a preferred embodiment the single colour diode light source  823   a  is a high wavelength blue colour diode light source, but it is also within an embodiment of the invention that it is a green colour diode light source  822   a , and for the illustrated embodiment it is an array of light emitting diodes, but a single light emitting diode may also be used. 
       FIG. 8   b  shows a projection illumination system according to a second embodiment of the fourth aspect of the invention. The system of  FIG. 8   b  comprises three projection modules  800   aa ,  800   bb ,  800   cc , where each module has diode light sources and a projection lens, with the projection lenses being arranged or optical aligned in a row so as to project light on the same projection screen  812 . 
     The module  800   aa  is the same as module  800   a  in  FIG. 8   a , while modules  800   bb ,  800   cc  are different to modules  800   b  and  800   c  in  FIG. 8   a  in that there is no UV or low wavelength blue light source in modules  800   bb  and  800   cc . The components used for modules  800   bb  and  800   cc  are as follows: a single colour diode light source  822   a  or  823   a , a polarizing filter  824 ,  825 , a liquid crystal display (LCD)  826 ,  827 , and a projection lens  828 ,  829 . In a preferred embodiment the single colour diode light source  823   a  is a blue colour diode light source or a green colour diode light source  822   a , and for the illustrated embodiment it is an array of light emitting diodes, but a single light emitting diode may also be used. 
       FIG. 9   a  shows a projection illumination system according to a third embodiment of the fourth aspect of the invention. The system of  FIG. 9   a  also comprises three projection modules,  900   a ,  900   b ,  900   c , where each module has diode light sources and a projection lens, with the projection lenses being arranged or optical aligned in a row so as to project light on the same projection screen  812 . 
     The module  900   a  corresponds to a simplified version of the module  800   a  in  FIG. 8   a , and the components used for module  900   a  are as follows: three light emitting diode (LED) arrays  801   a - 803   a  are arranged as diode light sources, where the first array  801   a  has diodes giving the colour red, the second array  802   a  has diodes giving the colour green, and the third array  803   a  has diodes giving the colour blue. In front of each LED array  801   a - 803   a  is arranged a polarizing filter  804 - 806 . A cross dichroic prism  810  directs the light from the three diode light sources  801   a - 803   a  through the LCD  808 , whereby a modulated colour image is formed and being projected by the lens  811 . In  FIG. 9   a  is also shown a projection screen  812  on which the image is being projected. For the system of  FIG. 9   a  the modules  900   b  and  900   c  are the same as modules  800   b  and  800   c  in  FIG. 8   a , respectively. 
       FIG. 9   b  shows a projection illumination system according to a fourth embodiment of the fourth aspect of the invention. The system of  FIG. 9   b  also comprises three projection modules,  900   aa ,  900   bb ,  900   cc , where each module has diode light sources and a projection lens, with the projection lenses being arranged or optical aligned in a row so as to project light on the same projection screen  812 . The module  900   aa  is the same as module  900   a  in  FIG. 9   a , while modules  900   bb  and  900   cc  are the same as modules  800   bb  and  800   cc  in  FIG. 8   b , respectively. 
       FIG. 10  shows a projection illumination system according to a fifth embodiment of the fourth aspect of the invention. The system of  FIG. 10  comprises only two projection modules,  10   a ,  10   b , where each module has diode light sources and a projection lens, with the projection lenses being arranged or optical aligned so as to project light on the same projection screen  812 . 
     The module  10   a  corresponds to the system of the third aspect of the invention illustrated in  FIG. 6   b , while module  10   b  is the same as module  800   b  in  FIG. 8   a . Thus, module  10   a  is a combination of part of the systems according to the first aspect of the invention illustrated in  FIG. 1   a  and part of the UV or low wavelength blue light source module illustrated in  FIG. 6   a , and the components used for module  10   a  are as follows: two light emitting diode (LED) arrays  801   a - 802   a  are arranged as diode light sources, where the first array  801   a  has diodes giving the colour red, the second array  802   a  has diodes giving the colour green; a third combined diode light source is provided and comprises a high wavelength blue colour diode light source  803   a , which may be an array of LED&#39;s, a UV or low wavelength blue light emitting diode  813   a  and a beam splitter  814 ; polarizing filters  804 - 806  and liquid circuit displays (LCD)  807 - 809  are provided in front of the two diode light sources  801   a ,  802   a  and the combined diode light source; and the three LCD&#39;s,  807 - 809 , are arranged on three sides of a cross dichroic prism  810 , with a projection lens  811  being arranged in front of a fourth side of the prism  810 . The discussion given above in connection with the system and components of  FIG. 6   b  is also valid for the components of module  10   a.    
       FIG. 11  shows a projection illumination system according to a sixth embodiment of the fourth aspect of the invention. The system of  FIG. 11  also comprises two projection modules,  11   a ,  11   b , where each module has diode light sources and a projection lens, with the projection lenses being arranged or optical aligned so as to project light on the same projection screen  812 . 
     The module  11   a  corresponds to a simplified version of the module  10   a  in  FIG. 10 , while module  11   b  is the same as module  10   b , which again is the same as module  800   b  in  FIG. 8   a . The components used for module  11   a  are as follows: two light emitting diode (LED) arrays  801   a - 802   a  are arranged as diode light sources, where the first array  801   a  has diodes giving the colour red, the second array  802   a  has diodes giving the colour green; a third combined diode light source is provided and comprises a high wavelength blue colour diode light source  803   a , which may be an array of LED&#39;s, a UV or low wavelength blue light emitting diode  813   a  and a beam splitter  814 ; polarizing filters  804 - 806  are provided in front of the two diode light sources  801   a ,  802   a  and the combined diode light source, which filters  804 - 806  are arranged on three sides of a cross dichroic prism  810 , with a liquid circuit displays (LCD)  808  and a projection lens  811  being arranged in front of a fourth side of the prism  810 . Furthermore, then for module  11   a , a filter glass  830  is inserted between the output side of the combined diode light source and the prism  810 . The use of the filter glass  830  is optional, but it may be used depending on the type of LED arrays, which are used in the system. The purpose of the filter is to smooth out and redirect the light produced by the LED&#39;s on to the optical axis, thereby removing rings of light, which may be generated by various LED types. It should be noticed, that the arrangement of a filter glass  830  in front of a diode light source or a combined diode light source may also be used for the other modules or systems of the present invention. 
       FIG. 12  shows a projection illumination system according to a seventh embodiment of the fourth aspect of the invention. The system of  FIG. 12  comprises three projection modules,  12   a ,  12   b ,  12   c , where each module has diode light sources and a projection lens, with the projection lenses being arranged or optical aligned in a row so as to project light on the same projection screen  812 . The module  12   a  is similar to module  900   b  in  FIG. 9   a , while modules  12   b  and  12   c  are similar to module  900   a  in  FIG. 9   a . When comparing module  12   a  to module  900   b  and modules  12   b  and  12   c  to module  900   a , some of the reference numerals have been changed. Thus, for module  12   a  a blue diode light source  823   a  is used, and the polarizing filter has reference numeral  805 , the LCD has numeral  808  and the projection lens has reference numeral  811 . For module  12   b , the LCD has numeral  826  and the projection lens has reference numeral  828 , while for module  12   c , the LCD has numeral  827  and the projection lens has reference numeral  829 . 
       FIG. 13  shows a projection illumination system according to an eight embodiment of the fourth aspect of the invention. The system of  FIG. 13  also comprises three projection modules,  13   a ,  13   b ,  13   c , where each module has diode light sources and a projection lens, with the projection lenses being arranged or optical aligned in a row so as to project light on the same projection screen  812 . The module  13   a  is similar to and has the same reference numerals as module  12   a  in  FIG. 12 , while modules  13   b  and  13   c  are similar to module  11   a  in  FIG. 11 . When comparing modules  13   b  and  13   c  to module  11   a , some of the reference numerals have been changed. For module  13   b , the LCD has numeral  826  and the projection lens has reference numeral  828 , while for module  13   c , the LCD has numeral  827  and the projection lens has reference numeral  829 . 
       FIG. 14  shows a projection illumination system according to a ninth embodiment of the fourth aspect of the invention. The system of  FIG. 14  also comprises three projection modules,  14   a ,  14   b ,  14   c , where each module has diode light sources and a projection lens, with the projection lenses being arranged or optical aligned in a row so as to project light on the same projection screen  812 . The module  14   a  is similar to module  800   bb  in  FIG. 8   b , while modules  14   b  and  14   c  are similar to modules  12   b  and  12   c , respectively, of  FIG. 12 . When comparing module  14   a  to module  800   bb  some of the reference numerals have been changed, and for module  14   a  a blue diode light source  823   a  is used, and the polarizing filter has reference numeral  805 , the LCD has numeral  808  and the projection lens has reference numeral  811 . 
     It should be understood that for the modules and systems described in connection with  FIGS. 8   a ,  8   b ,  9   a ,  9   b  and  10 - 14 , the light emitting diodes, diode arrays or single LED diodes discussed above for use in the systems of  FIGS. 1   a  and  1   b  may be used. In the same way, the polarizing filters, liquid crystal displays, prism and projection lens discussed above for use in the systems of  FIG. 1   a  and  1   b  may be used in the systems of  FIGS. 8   a ,  8   b ,  9   a ,  9   b  and  10 - 14 . Also the power supply circuitry an the circuitry for controlling image modulation of the LCD&#39;s illustrated and discussed above in connection with  FIGS. 2 and 5  for use in the systems of  FIGS. 1   a  and  1   b  may be used in the systems of  FIGS. 8   a ,  8   b ,  9   a ,  9   b  and  10 - 14 . For the systems of the fourth aspect of the invention having projection modules including a UV or low wavelength blue light source, then the discussion given above in connection with the UV or low wavelength blue light emitting diodes, the beam splitter  114  and the prism  110  of  FIGS. 6   a ,  6   b  and  6   c  is naturally also valid for the UV or low wavelength blue light source and the beam splitter  814  and prism  810  of these modules. 
     In order to obtain an optimal displayed video quality by a “three lens” projector using the principles of the fourth aspect of the invention and having three projection modules and thereby three projection lenses, the relative position of the projection modules and thereby the projection lenses must be adjusted and fine-tuned. The following parameters may have an influence on the adjustment and fine-tuning process: Selected picture size and distance from apparatus to projection screen or canvas. 
     The optical adjustment of a three lens projector corresponding to the projection illumination system shown in  FIG. 8   a  is illustrated in  FIG. 15 , which shows a projection system having a centre projection module A, a right projection module B, and a left projection module C. The three lens projector must be situated in the chosen distance to a projection screen or canvas, with the projection lenses front facing the canvas. The centre projection module, A, is turned on and the position of the centre module A is adjusted up or down in order to obtain the desired position of the projected picture (for example 1.5 meter from floor to bottom of picture). A test picture with grid may be displayed in order to help with the next adjustment steps described below. 
     The right projection module B is now adjusted so that the centre point of the picture displayed by module B is substantially on top of the centre point of the picture generated by the centre module A. This is achieved by moving the module B right/left and/or up/down into position. Finally the position of module B may be locked with securing bolts. 
     The left projection module C is also adjusted so that the centre point of the picture displayed by module C is substantially on top of the centre point of the picture generated by the centre module A. This is achieved by moving the module C right/left and/or up/down into position. Finally the position of module C may be locked with securing bolts. 
     For the above-described adjustment of the projection modules, it is the whole module including the projection lens that is adjusted. However, the lenses may be hold in a fixed position during this adjustment, while the remaining part of the projection module is adjusted. As the adjustment is left/right and up/down, the distance between the LCD&#39;s and the projection lens of a module is kept substantially constant during such an adjustment. 
     The adjustment and final tuning of the projector should be carried out either manually or automatically. However, it is preferred that the projector leaves the assembly line with pre-adjusted and fine-tuned settings (Fore example: 50″ picture size, with a distance of 2 meters from apparatus to canvas). 
       FIG. 16  is a front view schematically illustrating a first embodiment of movement directions of projection lenses used for the optical alignment of the projection illumination system shown in  FIG. 15 . In  FIG. 16 , the lenses B, A, C are secured to a frame of the projector. Optical alignment of the lenses B, A, C may be achieved by adjusting the securing bolts of the lenses. Centre lens A is aligned up/down, right and left lenses B, C are aligned up/down and left/right. However, optical alignment should preferably be preformed on production assembly line. 
       FIG. 17  is a front view schematically illustrating a second embodiment of movement directions of projection lenses, when the apparatus is situated up right (vertical), used for the optical alignment of the projection illumination system shown in  FIG. 15 . In  FIG. 17 , the lenses B, A, C are secured to a frame of the projector. Optical alignment of the lenses B, A, C may be achieved by adjusting the securing bolts of the lenses. Centre lens A and lenses B, C are aligned up/down. However, optical alignment should preferably be performed on production assembly line. 
     Since projecting at an angle causes distortion, it may necessary to fine-tune the position of the LCD&#39;s of projection modules B and C in  FIG. 15 . This may be achieved through use of digital keystone either manually or automatically through an integrated sensor system that may compensate for any distortion. Thus, using digital keystone, the displayed pictures from all LCD&#39;s in the projector must come together substantially or exactly on top of each other on the canvas. 
     Today most portable devices such as Cellular Telephones, PDA and Ipods etc. have a small standard 1″-2″ LCD display from which a user can read text, control menus and programs etc. However, the small size LCD displays in cellular telephones and small size portable equipment, in general, are unattractive for people to look at for long periods of time. People tend to get tired in their eyes and may get headache from watching a small LCD display for a long time. In addition, the broadband technology in cellular telephones and small size portable equipment today, makes it possible for consumers to enter video conferencing, downloading video or watching video directly from the Internet. This means that consumers, in the near future, for example will be able to surf on the Internet or watch a movie on their cellular telephone. Consequently, there is a need for an alternative way of displaying video/data on cellular telephones and small size portable equipment. 
     An illumination system according to one or more embodiments of the first and third aspects of the present invention may be used for providing an ultra small size image or video projector, which may be built into several types and sizes of portable equipment, thereby creating the possibility of displaying video or images from an ultra small projector within a cellular telephone, laptop, Ipaq, Ipod, portable devise etc. on to a canvas or white wall. Such an ultra small projector may be placed in the side, front side, backside, top, or bottom of the housing of the cellular telephone or portable devise. The light from the projector may be reflected inside a portable devise through an adjustable up and down mirror. As an example, when using an illumination system using the single diode LED&#39;s of the above-described example, then an acceptable quality of a projected image in the size of 32″ has been achieved on a canvas. 
     A small size image or video projector using an illumination system of the present invention may also be applied and put to use in several kinds of furniture, buildings, housing etc. For example the projector can be built into at table sofa, or a wall in a bedroom. In addition, such small size projectors can be clustered, meaning that several of the projectors can be situated on top of each other, around each other in a square or in a 365 degrees circle. Thus, displaying an image in up to 7 dimensions or more, giving an appearance of a holographic screen. 
     A “three lens” projector using the principles of the fourth aspect of the invention may be used to provide an inexpensive home cinema alternative to existing plasma/TFT/DLP screens and DLP/LCD/CTR projectors. The three lens projector apparatus may have several advantages: The projector can be produced relatively small in size. When compared to a plasma/TFT screen, which is very visible in a living room and takes a lot of space, the three lens projector will not be very visible in the room when turned off. The three lens projector can be placed on a table or mounted in the ceiling. In addition, since the three lens projector has a low power consumption and generates a low level of heat, the projector may be built into various types of furniture or a wall. The three lens projector will also have a very long lamp live of 10.000 to 20.000 hours. 
     It should be understood that various modifications may be made to the above-described embodiments and it is desired to include all such modifications and functional equivalents as fall within the scope of the accompanying claims.