Patent Publication Number: US-2007110386-A1

Title: Device having combined diffusing, collimating, and color mixing light control function

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention generally relates to light control devices, and more particularly to a device having combined light diffusing, collimating, and color mixing functions.  
      2. The Prior Arts  
      Conventionally, backlight units for liquid crystal displays (LCDs) or LCD TVs use cold cathode fluorescent lamps (CCFLS) or light emitting diodes (LEDs) as light source.  FIG. 1   a  is a schematic side view showing a conventional edge-lit backlight unit  10 . As shown in  FIG. 1   a , light emitted from a CCFL or LEDs  11  of the backlight unit  10  is directed into a side of a light guide plate  13  with the help of a reflector  12  and then redirected to the back of the display panel  40  of a LCD. Between the light guide plate  13  and the display panel  40 , there are usually configured with a diffusion sheet  15  for scattering the light from the light guide plate  13 , two prism sheets  16  and  17  whose respective prism structures are aligned orthogonally for focusing the scattered light from the diffusion sheet  15  into substantially parallel light beams, an optional polarization or anti-reflection film or layer  18 , and another diffusion sheet  19  to achieve further intensity uniformity of the light beams.  
      The diffusion sheet redirects light from one direction to many directions by scattering or refraction through embedded particles or rough surface. The prism sheet is a brightness enhancement optical film such as the Vikuiti™ BEF film provided by 3M Company or the Diaart™ prism sheet provided by Mitsubishi Rayon Co., Ltd. The polarization layer or film converts light from a lower degree of polarization to a higher degree of polarization. The polarization provided can be linear polarization, circular polarization, or elliptical polarization. For example, the Vikuiti™ DBEF film by 3M Company is one such linear polarization film. The anti-reflection layer or film prevents light transmission loss due to the reflection of light at the interface with different refractive indices.  
      The aforementioned edge-lit technique has a few disadvantages, especially for large-size LCDs in that the edge-lit backlight unit is unable to provide adequate light intensity, and large-size light guide plates are difficult to fabricate with practical cost and yield. Accordingly, most large-size LCDs adopt a direct-lit technique.  FIG. 1   b  is a schematic side view showing a conventional direct-lit backlight unit. As illustrated, multiple CCFLs  21  of the backlight unit  20  are arranged in parallel in front of the reflector  12  so as to direct light all toward the front of the reflector  12 . Similarly, between the CCFLs  21  and the display panel  40 , there are usually configured with the diffusion plate  14  and diffusion sheet  15 , prism sheets  16  and  17 , polarization or anti-reflection film or layer  18 , and another diffusion sheet  19 .  
      Besides using CCFLs as light source, LEDs can also be applied in direct-lit backlight unit, as shown in  FIG. 1   c . These LEDs  22  could be all white-light LEDs, or these LEDs may be assortments of red-light, green-light, and blue-light LEDs. For the former, the backlight unit  30  would have a structure very similar to that shown in  FIG. 1   b . For the latter, an additional light mixing plate  23  is usually positioned in front of the diffusion plate  14 , which provides multiple internal reflections so that the red, green, and blue lights from the LEDs are mixed to produce white light. However, the light mixing plate  23  usually provides a limited degree of light mixing so that additional distance between the light mixing plate  23  and the diffusion plate  14  is required to allow the residual red, green, and blue lights to further mix with each other as they propagate toward the diffusion plate  14 . This, however, imposes a serious constraint on how thin the backlight unit could be achieved.  
      As could be seen from the foregoing illustrations, in an abstract sense, the reflector, the diffusion plate and sheets, the prism sheets, the light guide plate, the light mixing plate, and the polarization and anti-reflection film or layer are light control devices which manipulate, convert, or transform their incident light in one way or another into having the desired optical characteristics. From the view point of the display panel, what it requires is simply a planar light source having a high degree of intensity uniformity and brightness, and, for color displays, a desired color mixing delivering the required color features such as color temperature and optimal gamut mapping (Billmeyer and Saltzmain&#39;s Principles of Color Technology, 3rd Ed., Roy&#39;s Berns, John Wiley &amp; Sons Inc). However, no matter how brilliant they are arranged, the limitation inherent in linear light sources such as CCFLs and point light sources such as LEDs simply prohibit them to provide the planar light required by the display panel and, therefore, all the aforementioned light control devices are introduced to make up the discrepancy.  
      As LCDs have become the mainstream display technology, a very large number of techniques for various kinds of light control devices have been disclosed in the related arts such as, just to name a few of them with respect to diffusion or prism sheets, U.S. Pat. Nos. 6,280,063 B1, 6,322,236 B1, 6,570,710 B1, 6,845,212 B2. The objectives of these light control devices could be generally categorized into two categories: (1) to achieve superior intensity uniformity by diffusing or scattering light into various directions; and (2) to achieve brightness enhancement by focusing or collimating light beams into a proper viewing angle (that is, the maximum angle at which the minimum contrast of an image can be viewed). These light control devices are generally effective but, unfortunately, only to a certain degree, mostly because they process the incident light regardless of its intensity distribution while, in fact, the incident light has a significantly non-uniform distribution of light intensity as it enters the devices through the light incidence planes of these devices. The distribution or the variations of light intensity over a plane or surface (e.g., the light incidence plane) in space is referred to as “spatial intensity distribution” hereinafter throughout this specification.  
      To explain how the non-uniform spatial intensity distribution is resulted,  FIG. 1   d  provides schematic front views to a number of scenarios of light source arrangement in a direct-lit backlight unit. The diagram (a) of  FIG. 1   d  is a typical array arrangement of white-light LEDs, the diagram (b) of  FIG. 1   d  is a typical arrangement of red-light (R), green-light (G), and blue-light (B) LEDs, and the diagrams (c) and (d) are two configurations of the CCFLs. As should be obvious from  FIG. 1   d , due to the planar arrangement of a limited number of the point light sources such as LEDs, or linear light sources such as CCFLs, it is inevitable to have some significantly non-uniform spatial intensity distribution on the light incidence plane of a light control device arranged in front of one of these light sources.  
      To illustrate this non-uniform spatial intensity distribution, a simulation is conducted by having four evenly spaced white-light LEDs on a 50 mm×50 mm plane in front of a reflector, just like that of a miniature, ordinary direct-lit backlight unit as illustrated in  FIG. 1   d  (a). Each of the LEDs has a 4-mm radius and a luminous flux of 8 lumen, and the reflector has a reflection efficiency of 98%.  FIG. 2   a  is a 3D presentation of the calculated illuminance of the miniature light source over a 50 mm×50 mm surface. As can be seen from  FIG. 2   a , four sharp spikes are formed around the four LEDs. However, without regarding to the spatial intensity distribution of the light source, the conventional light control techniques process their incident light regardless of the light intensity. The result is that the sharp spikes are indeed smoothed out but only to a limited extent as shown in  FIG. 2   b  and, therefore, additional light control devices are employed as shown in  FIGS. 1   a ˜ 1   c . This, inevitably, causes a great deal of power loss as the light propagates through the light control devices. Then, a sophisticated heat dissipation design is required to ventilate the heat produced from the excessive power loss. The scenario does not stop here as, to make up the loss power, additional light control devices are introduced for brightness enhancement which, in turn, adds up the product cost. In addition, as the lighting efficiency of LEDs is continuously advanced and thereby a less number of LEDs are required, the non-uniform spatial intensity distribution and the inadequacy of conventional light control devices are even more obvious.  
      Furthermore, for direct-lit backlight units based on assortments of red-light, green-light, and blue-light LEDs, due to the color and the variations of the manufacturing process, each of the LEDs inevitably exhibits a specific spectral profile (i.e., a profile of the light intensity at each wavelength in the interested wavelength band). Then, depending on how these LEDs are arranged, the incident light to a light control device has a specific distribution of spectral profile from color-mixing the various colored lights of the LEDs on the device&#39;s light incidence plane. The distribution or the variations of spectral profile over a surface or plane in space is referred to as “spatial spectral distribution” hereinafter throughout this specification. None of the conventional light control devices has addressed the problem of shaping or transforming its incident light&#39;s spatial spectral distribution into a desired spatial spectral distribution of the LCD. Conventionally, this problem is left to the bulky light mixing plate alone and/or complex color sensing elements and circuits to solve and, as a result, the thickness of LCD is hard to reduce.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention is to provide a light control device for use with a light source unit to obviate the foregoing shortcomings of the conventional approaches. A major objective of the present invention is to achieve a very high degree of intensity uniformity within a proper viewing angle without the use of excessive and multiple diffusing and focusing mechanisms. As such, the problems associated with complicated manufacturing process, high product cost, excessive light power loss, and extraneous heat dissipation could all be resolved satisfactorily, if not entirely, through the present invention&#39;s multi-function integration and reduced material usage. Another major objective of the present invention is to help shaping the desired spatial spectral distribution for the target application from the red, green, and blue lights of the light source unit. As such, a less complicated light mixing mechanism could be used and the thickness of the backlight unit as well as power consumption of the LCD could be reduced profoundly.  
      To achieve the foregoing objectives, the light control device of the present invention is positioned on the path of light from the light source unit. The light control device provides at least one of the light control functions, namely the diffusion, collimation, and color mixing. However, instead of processing the incident light regardless of its intensity distribution as in the conventional approaches, the light control function provided by the light control device, be it diffusing, collimating, or color mixing, has a spatial distribution of its processing power corresponding to a spatial intensity distribution and/or spatial spectral distribution of the incident light.  
      The light control device of the present invention could also combine two or more of the light control functions into a single device. However, this is not a simple stacking of multiple conventional light control devices. At least one of the light control functions of the present invention, most importantly, has a spatial distribution of its processing power corresponding to a spatial intensity distribution and/or the spatial spectral distribution of its incident light. In one embodiment of the present invention, the light control device contains a transparent substrate having a diffuser structure, a collimator structure, and a color mixing structure. The diffuser structure is arranged across the light incident plane which scatters the incident light in all directions so as to achieve a high degree of uniformity. The diffuser structure has a spatial distribution in terms of the degree of haze corresponding to the spatial intensity distribution of the incident light on the light incidence plane. In other words, at a position on the light incidence plane, the diffuser structure there has a higher (or lower) degree of haze if the light intensity at the position is stronger (or weaker).  
      In this embodiment, the collimator structure is arranged on the light emission plane (i.e., where light is emitted out of the device) which directs the scattered light from the diffuser structure into substantially collimated light beams within a proper viewing angle so as to enhance the luminance of the light emitted from the device. The collimator structure contains a number of microstructures and the microstructures could have a spatial distribution in terms of their geometric properties and/or refractive indices corresponding to the spatial intensity distribution of (1) the incident light on the light incidence plane (i.e., the light to the light control device), or (2) the incident light on the light emission plane (i.e., the light to the collimator structure which is also the light emitted from the preceding diffuser structure). In other words, the microstructure at a position on the light emission plane has specific geometric properties and/or a specific refractive index if the light incident to the light incident plane (i.e., to the light control device) has a specific intensity at a position on the light incidence plane corresponding to that position on the light emission plane. Or, the microstructure has specific geometric properties and/or a specific refractive index at that specific position on the light emission plane if the light incident to the light emission plane (i.e., to the microstructures) has a specific light intensity at that position.  
      In this embodiment, the color mixer structure contains additives dispersed in the diffuser structure, collimator structure, or both. The additives may include appropriate dyes and/or pigments for color intensity absorption, nano/micro particles for light scattering, or phosphors and/or fluorescent materials for light absorption and reemission. In an alternative embodiment, these dyes, pigments, nano/micro particles, phosphors, and/or fluorescent materials could be mixed with adequate resin and coated on the light emission plane as a separate coating layer. The distribution of the additives may depend on a spatial spectral distribution over an appropriate range of wavelength of (1) the incident light on the light incidence plane (i.e., the light to the light control device), or (2) the incident light on the light emission plane (i.e., the light to the color mixing structure). The dyes, pigments, nano/micro particles, phosphors, and/or fluorescent materials of the color mixing structure shift, transform, or convert the spatial spectral distribution of the incident colored light to match a desired spatial spectral distribution over the range of wavelength so that a better color mixing could be achieved for the target application of the light control device.  
      The light control device could be adopted in various applications in addition to being integrated as part of the backlight unit of a LCD display. The light control device could also be integrated with various types of lighting devices such as table or floor lamps where a light source unit having a non-uniform spatial intensity distribution is involved and where better color-mixed, uniform and collimated light beams are to be achieved.  
      The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1   a  is a schematic side view showing a conventional edge-lit backlight unit.  
       FIG. 1   b  is a schematic side view showing a conventional direct-lit backlight unit utilizing CCFLs.  
       FIG. 1   c  is a schematic side view showing a conventional direct-lit backlight unit utilizing LEDs.  
       FIG. 1   d  provides schematic front views to a number of scenarios of light source arrangement in a direct-lit backlight unit.  
       FIG. 2   a  is a 3D presentation of the calculated illuminance of a miniature light source unit containing four LEDs over a 50 mm×50 mm surface  
       FIG. 2   b  is a 3D presentation of the calculated illuminance of the light from the miniature light source unit of  FIG. 2   a  after they have passed through a conventional prism sheet.  
       FIG. 2   c  is a schematic side view of a light control device according to the present invention used in the simulations of  FIG. 2   d.    
       FIG. 2   d  is a 3D presentation of the calculated illuminance of the light from the miniature light source unit of  FIG. 2   a  after they have passed through the light control device of  FIG. 2   c.    
       FIG. 3   a  is schematic model showing the light control devices of a conventional backlight unit arranged in parallel along the Z-axis of a Cartesian coordinate system.  
       FIG. 3   b  is a schematic model showing a conventional diffusion sheet laid on the X-Y plane of a coordinate system and scattering an incident light beam propagating along the Z-axis.  
       FIGS. 4   a ˜ 4   e  are schematic side views showing various application scenarios of the present invention in LCDs.  
       FIGS. 5   a ˜ 5   e  are schematic side views showing various variations of a first embodiment of the light control device according to the present invention.  
       FIGS. 6   a ˜ 6   e  are schematic front views showing various spatial patterns of the diffuser structure according to the present invention.  
       FIGS. 7   a  and  7   b  are schematic side views showing an anti-reflection layer or a polarization layer is integrated with the first embodiment of the light control device of the present invention.  
       FIGS. 8   a  and  8   b  are schematic side views showing other variations of the first embodiment of the light control device of the present invention.  
       FIG. 9  is a schematic view of a portion of the light incident plane where different colored areas are formed by a red-light, a green-light, and a blue-light LED.  
       FIGS. 10   a ,  10   b , and  10   c  are schematic side views showing other embodiments of the light control device according to the present invention.  
       FIGS. 11   a  and  11   b  are schematic side views showing various approaches in obtaining the diffuser structure&#39;s spatial pattern.  
       FIGS. 12   a ˜ 12   c  are schematic diagrams showing the effects of dyes/pigments, phosphors/fluorescent materials, and nano/micro particles on spectral profile respectively. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The following descriptions are exemplary embodiments only, and are not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention as set forth in the appended claims.  
      The present invention provides a novel light control device which combines at least one of the light diffusing, collimating, and color mixing functions, and, at least one of the functions has a spatial distribution of its processing power configured corresponding to a spatial intensity distribution and/or a spatial spectral distribution of the incident light. A number of terms used throughout this specification have the following defined meanings: 
      Combination The integration of at least two light control functions. The integrated functions are said to be “directly combined” if they are independent of each other. Two integrated functions are said to be “interactively combined” if one function is dependent upon the output of the other function.     Diffusing The process of changing of the angular distribution of a beam of radiant flux by a transmitting material or a reflecting surface such that flux incident in one direction is continuously distributed in many directions (ASTM E284). The term “diffusing” is used interchangeably with the term “scattering.”    Collimating The process of minimizing divergence and convergence to make the light beams as parallel as possible. The term “collimating” is used interchangeably with the term “focusing.”    Color mixing The combination of the light of “primary” colors (red, green, and blue) to make colors in according with CIE 1931 standard.     Spatial distribution The schematic arrangement of a particular feature in space.     Uniformity Uniformity of a feature is the ratio of the minimum and the average value of the feature (e.g., when the ratio is close to 1, it is said to be substantially uniform and, when the ratio is close to 0, it is said to be substantially non-uniform).    

      To explain the idea behind the present invention, using the edge-lit backlight unit shown in  FIG. 1   a  as example, each of the light control device could be considered mathematically as an operator {circumflex over (M)} using Jones/Muller-like matrix (S. Huard, Polarization of Light, John Wiley &amp; Sons, New York, 1997) expression transforming the incident light to the device into the emitted light from the device. For example, assuming that {tilde over (E)} in  represents the light emitted from the light guide plate  13  and {tilde over (E)} out  represents the light emitted to display panel  40  by the diffusion sheet  19 , the relationship between {tilde over (E)} in  and {tilde over (E)} out  could be expressed as:
 
 {tilde over (E)}   out   ={circumflex over (M)}   19   {circumflex over (M)}   18   {tilde over (M)}   17   {circumflex over (M)}   16   {circumflex over (M)}   15   {tilde over (E)}   in 
 
 where {circumflex over (M)} ij  is the operator representing the light control function provided by the light control device ij (i=1, j=1 to 9). For example, {circumflex over (M)} 15  represents the function of the diffusion sheet  15 . To facilitate the subsequent description, these devices could be imagined to be positioned in parallel along the Z-axis of a Cartesian coordinate system as illustrated in  FIG. 3   a  in which, for simplicity sake, the thickness of the devices is ignored. 
 
      The meaning of the operator {circumflex over (M)} is explained as follows using the diffusion sheet  15  as an example. A conventional diffusion sheet such as the diffusion sheet  15  provides the diffusing or scattering function achieved by a number of means such as surface roughness and a coating of appropriate material, just to name a few. No matter how it is achieved, the diffusing or scattering function at a position (x, y, z) of the diffusion sheet  15  as shown in  FIG. 3   a  could be generally characterized by a degree of haze h(x, y, z) as defined by the American Standard Test Method (ASTM) E284. Again, for simplicity sake, the Z coordinate is ignored, reducing h(x, y, z) to h(x, y). In addition, since the distribution of the h(x, y) for most conventional diffusion sheets is essentially uniform, the distribution of h(x, y) is further simplified to a constant h. With the foregoing simplification, the operator {circumflex over (M)} 15  could be considered a process transforming a beam of the incident light {tilde over (E)} in-15  into the diffusion sheet  15  with an incident angle θ i  into a beam with a polar angle θ r  and an azimuthal angle φ r . Therefore, the relationship between the incident light {tilde over (E)} in-15  and the emitted light {tilde over (E)} out-15  could be expressed as:
 
 {tilde over (E)}   out-15 (θ r ,φ r )= {circumflex over (M)}   15 ( h ) {tilde over (E)}   in-15 (θ i )
 
 To give better understanding of the above formula,  FIG. 3   b  is a schematic perspective view showing a conventional diffusion sheet on the X-Y plane of a Cartesian coordinate system and scattering an incident light beam propagating along the Z-axis. In the illustration, the incident light beam I in  represents a portion of {tilde over (E)} in-15 (θ i =0), and the scattered light beam I out  represents a portion of {tilde over (E)} out-15 (θ r , φ r ) where θ r  is the included angle between I out  and Z-axis while θ r  is the included angle between the projection of I out  on the X-Y plane and the X-axis. More specifically, the degree of haze h alone determines the scattering function of the operator {circumflex over (M)} 15 . This is why it is mentioned earlier that the conventional diffusion sheets process the incident light regardless of the intensity distribution. Please note that some conventional diffusion sheets have the degree of haze varied in a predetermined or random manner and therefore h(x, y) is not a constant. In this way, the foregoing formula would become:
 
 {tilde over (E)}   out-15 ( x, y, θ   r ( x, y ), φ r ( x, y ))= {circumflex over (M)}   15 ( x, y, h ( x, y )) {tilde over (E)}   in-15 ( x, y, θ   i ( x, y ))
 
 However, despite that h(x, y) indeed has some form of distribution, h(x, y) still has no correlation to the light intensity at the position (x, y) and the incident light is still processed regardless of its intensity distribution. 
 
      The emitted light {tilde over (E)} out-15  then propagates and becomes the incident light {tilde over (E)} in-16  to the prism sheet  16 , which is confined to a viewing angle θ v  when exits from the prism sheet  16 . A conventional prism sheet such as the prism sheet  16  provides the collimating or focusing function achieved by the microstructures configured on the prism sheet. The collimating or focusing function at a position (x, y, z) of the prism sheet  16  as shown in  FIG. 3   a  could be generally characterized by a parameter m(x, y, z). Using  FIG. 2   c  as an example, the parameter m(x, y, z) is an abstraction of the collimating or focusing capability determined by the geometric properties such as the shape of the microstructure, and the height (e.g., 25 μm), vertex angle (e.g., 90°), and width (i.e., 50 μm) of the prism-shaped microstructure at the position (x, y, z). Again, for simplicity sake, the Z coordinate is ignored, reducing m(x, y, z) to m(x, y). In addition, since the shape and the arrangement of the microstructures are essentially regular for conventional prism sheets, contributing to a rather uniform distribution of the parameter m(x, y), m(x, y) is further simplified to a constant m when the size of the device is sufficiently large. With the foregoing simplification, the relationship between the incident light E in-16  and the emitted light {tilde over (E)} out-16  could be expressed as:
 
 {tilde over (E)}   out-16 (θ v ,φ′ r )= {circumflex over (M)}   16 ( m ) {tilde over (E)}   in-16 (θ r , φ r )
 
 where φ′ r  and φ r  are not necessarily the same. Again, the parameter m alone determines the focusing function of the operator {circumflex over (M)} 16 . This is why it is mentioned earlier that the conventional prism sheets process the incident light regardless of the intensity distribution. Please note that some conventional prism sheets have the microstructures with different geometric properties randomly arranged and therefore m(x, y) is not a constant. In this way, the foregoing formula would become:
 
 {tilde over (E)}   out-16 ( x, y θ   v ( x, y ), φ′ r ( x, y ))= {circumflex over (M)}   16 ( x, y, m ( x, y )) {tilde over (E)}   in-16 ( x, y, θ   r ( x, y ),φ r ( x, y ))
 
 However, despite that m(x, y) indeed has some form of distribution, m(x, y) still has no correlation to the light intensity at the position (x, y) and the incident light is still processed regardless of its intensity distribution. 
 
      However, as mentioned earlier, since all current light source units cannot provide a true planar light, a light control device would inevitably perceive a non-uniform spatial intensity distribution up to certain extent as the light from a light source unit entering the light control device. Therefore, instead of processing the incident light regardless of its spatial intensity and/or spectral distribution as in the conventional approaches, the light control device proposed by the present invention contains at least one of the following light control functions: diffusion (or scattering), collimation (or focusing), and color mixing, and the light control function has a spatial distribution of its processing power corresponding to the spatial intensity distribution and/or the spatial spectral distribution of the incident light. Again, assuming the light control device of the present invention is positioned along the Z-axis parallel to the X-Y plane of a Cartesian coordinate system similar to that of  FIG. 3   a , and again ignoring the Z coordinate, the light incident to the light control device would have a spatial intensity distribution {tilde over (E)} in-LCD  and/or a spatial spectral distribution λ in-LCD  on, for example, the light incident plane, where the subscript LCD stands for “Light Control Device.” In the following, the light intensity and the spectral profile at a position (x, y) are expressed as {tilde over (E)} in-LCD (x, y) and λ in-LCD (x, y) respectively. The spatial spectral distribution and the spectral profile will be described in more details later.  
      For example, a light control device of the present invention having combined diffusing and collimating functions to replace the diffusion sheet  15 , and the prism sheets  16  and  17  of  FIG. 1   a . Then, the relationship between {tilde over (E)} in  and {tilde over (E)} out  of  FIG. 1   a  could be expressed in a simplified manner as:
 
{tilde over (E)} out ={circumflex over (M)} 19 {circumflex over (M)} 18 {circumflex over (M)} LCD {tilde over (E)} in 
 
 where {circumflex over (M)} LCD  is the operator representing the light control function provided by the light control device of the present invention. However, please note that {circumflex over (M)} LCD ≠{circumflex over (M)} 17 {circumflex over (M)} 16 {circumflex over (M)} 15  (i.e., a simple stacking of the conventional diffusion sheet  15 , and prism sheets  16  and  17 ). For this example, {circumflex over (M)} LCD  could be expressed as:
 
 {circumflex over (M)}   LCD ( x, y, h ( x, y ),  m ( x, y ))= {circumflex over (M)}   collimator ( x, y, m ( x, y )) {circumflex over (M)}   diffuser ( x, y, h ( x, y ))
 
 The combined diffusing function is represented by the operator {circumflex over (M)} diffuser  and the combined collimating function is represented by the operator {circumflex over (M)} collimator . More specifically, the degree of haze h(x, y) and the collimating capability m(x, y) at a position (x, y) are both functions of the light intensity at the position (x, y), {tilde over (E)} in-LCD (x, y):
 
 h ( x, y )=ƒ h ( {tilde over (E)}   in-LCD ( x, y ))
 
 m ( x, y )=ƒ m ( {tilde over (E)}   in-LCD ( x, y ))
 
 In other words, the degree of haze and the collimating capability have spatial distributions corresponding to the spatial intensity distribution of the incident light on the light incidence plane of the light control device. 
 
      Based on the same model, different types of light control devices of the present invention could be represented, just to give a few examples, as follows:
 
 {circumflex over (M)}   LCD ( x, y, h ( x, y ))= {circumflex over (M)}   17   {circumflex over (M)}   16   {circumflex over (M)}   diffuser ( x, y, h ( x, y ))
 
 where a diffusing function tailored for the spatial intensity distribution of the incident light is combined with the conventional collimating functions provided by the prism sheets  16  and  17 , or
 
 {circumflex over (M)}   LCD ( x, y, m ( x, y ))= {circumflex over (M)}   collimator ( x, y, m ( x, y )) {circumflex over (M)}   15 
 
 where a collimating function tailored for the spatial intensity distribution of the incident light is combined with the conventional diffusing function provided by the diffusion sheet  15 . Please also note that the light control device could also contain only the diffusing or collimating function as follows:
 
{circumflex over (M)} LCD ( x, y, h ( x, y ))={circumflex over (M)} diffuser ( x, y, h ( x, y )),
 
or
 
 {circumflex over (M)}   LCD ( x, y, m ( x, y ))= {circumflex over (M)}   collimator ( x, y m ( x, y ))
 
 Even though the foregoing discussion didn&#39;t cover the color mixing function, one could easily image and extend the mathematical model above to the color mixing function. For example, a light control device containing only the color mixing function that corresponds to the spatial spectral distribution of the incident light could be expressed as follows:
 
 {circumflex over (M)}   LCD ( x, y, α ( x, y ))= {circumflex over (M)}   color-mixer ( x, y, α ( x, y ))
 
and
 
α( x, y )=ƒ α (λ in-LCD ( x, y ))
 
 where α(x, y) is an abstraction of the color mixing capability achieved by appropriate dyes, pigments, nano/micro particles, phosphors, and/or fluorescent materials at the position (x, y), and α(x, y) is a function of the spectral profile at the position (x, y), λ in-LCD (x, y). More details about the color mixing function will be given later. 
 
      The foregoing model could be extended to include other parameters of the light control functions. For example,
 
 {circumflex over (M)}   LCD ( x, y, h ( x, y ), RI( x, y ),  m ( x, y ))= {circumflex over (M)}   collimator ( x, y , RI( x, y ),  m ( x, y )) {circumflex over (M)}   diffuser ( x, y, h ( x, y )),
 
and
 
RI( x, y )=ƒ RI ( {tilde over (E)}   in-LCD ( x, y ))
 
 where RI stands for the refractive index of the material used for the microstructure formation. As should be well known to people skilled in the related art, a higher RI is able to collimate and confine light beams into a narrower viewing angle. For another two examples,
 
  {circumflex over (M)}   LCD ( x, y, h ( x, y ), RI( x, y ),  m ( x, y ), α( x, y ))= {circumflex over (M)}   collimator ( x, y , RI( x, y ),  m ( x, y )) {circumflex over (M)}   diffuser ( x, y, h ( x, y ), α( x, y ))
 
 where the color mixing function is integrated with the diffusing process, and
 
 {circumflex over (M)}   LCD ( x, y, h ( x, y ), RI( x, y ),  m ( x, y ), α( x, y ))= {circumflex over (M)}   collimator ( x, y , RI( x, y ),  m ( x, y ), α( x, y )) {circumflex over (M)}   diffuser ( x, y, h ( x, y ))
 
 where the color mixing function is integrated with the collimating process. What the above two formulas suggest is that the diffusion process, or the collimating process, or both could incorporate the color mixing function to transform the spectral profile λ in-LCD (x, y) at any position (x, y) so that a desired spatial spectral distribution required by the lighting application could be achieved. In the following, exemplary embodiments about such integration will be described in more details. 
 
      Please be noted that the above mentioned diffusing, collimating and color mixing functions are individually corresponding to the same spatial intensity and/or spectral distribution of the incident light on, for example, the light incidence plane. This is referred as a “direct combination” of the light control functions. The light control device of the present invention could also “interactively combine” two or more of the light control functions. The interactive combination of light control functions have their processing powers spatially distributed correspondingly to the output of the preceding light control function along the path of light. As such, using the above two formulas as example, an interactive combination operator {circle around (x)} is introduced as follows:
 
 {circumflex over (M)}   LCD ( x, y, h ( x, y ), RI( x, y ),  m ( x, y ), α( x, y ))= {circumflex over (M)}   collimator ( x, y , RI( x, y ),  m ( x, y )) {circle around (x)} {circumflex over (M)}   diffuser ( x, y, h ( x, y ), α( x, y ))
 
and
 
 {circumflex over (M)}   LCD ( x, y, h ( x, y ), RI( x, y ),  m ( x, y ), α( x, y ))= {circumflex over (M)}   collimator ( x, y , RI( x, y ),  m ( x, y ), α( x, y )){circle around (x)} {circumflex over (M)}   diffuser ( x, y, h ( x, y ))
 
 The symbol {circle around (x)} means that, for a light control function (i.e., diffusion in this example) in front of another light control function (i.e., collimation in this example) along the path of light, the latter light control function could have its light control power spatially distributed correspondingly to a spatial intensity distribution produced by the light output from the former. More specifically, the diffusing function {circumflex over (M)} diffuser  is configured correspondingly to the spatial intensity distribution {tilde over (E)} in-LCD  of the incident light into the light control device; while the {circumflex over (M)} collimator  could be configured correspondingly either to {tilde over (E)} in-LCD  (i.e., in a direct combination scenario), or to the spatial intensity distribution {tilde over (E)} out-diffuser  of the light output by the diffusing function (i.e., in an interactive combination scenario). 
 
      Please note that the foregoing model could be extended to directly combine other conventional light control functions such as a polarizer and anti-reflection coating. For example, a light control device of the present invention could combine the diffusion sheets  15  and  19 , the prism sheets  16  and  17 , and the polarization or anti-reflection film or layer  18  of  FIG. 1   a . Then, the relationship between {tilde over (E)} in , and {tilde over (E)} out  could be expressed as:
 
{tilde over (E)} out ={circumflex over (M)} LCD {tilde over (E)} in 
 
      In the following, the above described model is applied in various embodiments of the present invention. As a brief summary, the present invention covers (1) a light control device containing one of the three major light control functions: diffusing function, collimating function, and color mixing function, which is tailored to the spatial intensity and/or spectral distribution of the incident light, and (2) a light control device combining two or more light control functions and at least one of them is tailored to the spatial intensity and/or spectral distribution of the incident light to the light control device (i.e., in a direct combination scenario) or of its own incident light (i.e., in an interactive combination scenario). As there are a very large number of combinations and these combinations cannot be exhausted completely. For simplicity, only some exemplary embodiments are discussed as follows and the implementation details covered by these embodiments could be extended to those embodiments not covered here.  FIGS. 4   a  and  4   b  are schematic side views showing the light control device  100  of the present invention applied in LCDs utilizing edge-lit and direct-lit backlight units respectively. As illustrated and in comparison to  FIGS. 1   a ,  1   b  and  1   c , the light control device  100  is positioned in the path of the light from the CCFLs  11 ,  21  or LEDs  22  to the back of the display panel  40 , entirely replacing the conventional light control devices. In some other application scenarios such as those illustrated in  FIGS. 4   c  and  4   d , the light control device  100  of the present invention could also be combined with one or more diffusion sheets  15  or diffusion plates, or with one or more prism sheets  16  or other type of brightness enhancement films, or both.  FIG. 4   e  is yet another application scenario where two or more of the light control devices  100  are employed together in a direct-lit backlight unit. Besides being integrated as part of the backlight unit of a LCD as shown in  FIGS. 4   a ˜ 4   e , the light control device of the present invention could actually be integrated with other lighting devices such as various kinds of lamps for converting the light from a non-uniform light source unit of these lighting devices into collimated light beams having a high degree of uniformity and a desired spatial spectral distribution.  
       FIGS. 5   a ˜ 5   e  are schematic side views showing a number of variations of a first embodiment of the light control device according to the present invention. As illustrated, the present embodiment mainly contains a transparent substrate  110  made of polymer, copolymer, composite, or glass material, which has over 70% total light transmittance in the wavelength of 420˜680 nm region. However, the present invention does not impose a specific requirement on the transparency of the substrate  110 . The substrate  110 , positioned on the path of the light from a light source unit made of CCFLs  21  and the reflector  12 , has a light incidence plane  112  through which the light from the light source unit enter the substrate  110 , and a light emission plane  114  opposite to the light incidence plane  112  and through which the light leaves the substrate  110 . On the light incidence plane  112 , a diffuser structure  120  is configured to scatter the incident light into various directions. The diffuser structure  120  has a spatial pattern in terms of the degree of haze (generally, between 3%˜95%) and the spatial pattern is arranged correspondingly to the spatial intensity distribution of the incident light on the light incidence plane  112 , covering 1%˜99% of the area of the light incidence plane  112 . In other words, at positions where the light intensity is stronger, the diffuser structure  120  has a higher degree of haze (i.e., scattering light more intensively) at these positions. Please note that, if the light control device is used along with other diffusion sheets or plates, the spatial pattern could cover a smaller area (e.g., 1-20%) while, if there is no other diffusion sheets or plates used, the spatial pattern could cover a much larger area (e.g., 70-99%). Please note that the term “structure” is used to refer to an appropriate mechanism to achieve a desired function. For example, the diffuser structure could be implemented by surface roughness to the light incidence plane, or it could be implemented by a coating layer with embedded particles on the light incidence plane.  
      Using the light source unit of  FIG. 2   a  as example, a number of exemplary patterns of the diffuser structure  120  (as in  FIGS. 5   a ˜ 5   e ) on the light incidence plane  112  (as in  FIGS. 5   a ˜ 5   e ) are illustrated in  FIGS. 6   a ˜ 6   e , where a darker point stands for a higher degree of haze. As should be obvious from  FIGS. 6   a ˜ 6   e , for a position (x, y) on the light incidence plane  112  (as in  FIGS. 5   a ˜ 5   e ) projected on the X-Y plane of a Cartesian coordinate system, the degree of haze of the diffuser structure  120  (as in  FIGS. 5   a ˜ 5   e ) at that position (x, y) has a functional relationship ƒ h  with the intensity of the incident light at that position (x, y). Examples of the function ƒ are as follows:
 
 h ( x, y )= c   1   ×{tilde over (E)}   in-LCD ( x, y )
 
 where c 1  is a constant for all positions (x, y)
 
 h ( x, y )= c   2   ×{tilde over (E)}   in-LCD ( x, y )
 
 where c 2  is a constant for all positions (x, y)
 
 In contrast, for a conventional diffusion sheet, its degree of haze distribution could be described as:
 
 h ( x, y )= c   3 
 
 where c 3  is essentially a constant for all (x, y)
 
      As shown in  FIGS. 5   a ˜ 5   e , on the light emission plane  114  of the light control device  100 , a collimator structure  130  containing a number of microstructures  132  in the micrometer (i.e., 1˜10 3  μm) or sub-micrometer (i.e., 1˜10 −2  μm) dimension is configured to focus the scattered light from the diffuser structure  120  into collimated light beams having an appropriate viewing angle (preferably, between 60°˜120°) so as to improve the luminance of the collimated light beams. The microstructures  132  may possess different geometric properties in terms of their shapes, and the various parameters associated with the shapes. For example, the microstructures  132  could have one of the following shapes: prism, pyramid, rectangle, spherical lens, aspherical lens, lenticular lens, fresnel lens, holographic elements, etc. And, using the prism shape as an example, the geometric parameters associated with the prism shape may include: the height, vertex angle, bottom width, etc., of each prism. The subject matter of the present invention is not about geometric properties of the microstructures  132 ; many such techniques have already been disclosed in the related arts. What characterizes the present invention is that the collimating capability determined by the geometric properties of the microstructures  132  could be substantially uniform across the light emission plate  114 , as shown in  FIG. 5   a , or the microstructures  132  could have a spatial distribution in terms of their geometric properties corresponding to the spatial intensity distribution of the incident light on the light incidence plane  112 , as shown in  FIGS. 5   b ˜ 5   e . In other words, at positions where the light intensity is stronger, the microstructures  132  there have geometric properties different from those at positions where the light intensity is weaker. Please note that, in alternative embodiments using interactive combination, the microstructures  132  could have a spatial distribution in terms of their geometric properties corresponding to the spatial intensity distribution of the light into the microstructures  132  on the light emission plane  114 , instead of on the light incidence plane  112 .  
      In an alternative embodiment, the microstructures of the collimator structure could have substantially regular or randomly distributed geometric properties (therefore, a rather uniform distribution of collimating capability). Instead, the refractive indices (RI) of the microstructures (e.g., in the range 1.55˜1.75) have a spatial distribution corresponding to the spatial intensity distribution of the incident light to the light control device (for direct combination) or to the collimator structure (for interactive combination). This could be achieved by selectively applying materials of specific refractive indices at specific positions so as to form the microstructures. Using geometric properties and using the refractive indices of the microstructures to conform to a spatial intensity distribution could be jointly or separately implemented.  
      Based on the aforementioned principle of combining multiple light control functions, again using  FIG. 5   a  as example, the light control device  100  of the present invention could further contain one ore more anti-reflection and/or polarization layers to further enhance the performance of the present invention, as illustrated in  FIGS. 7   a  and  7   b . In  FIG. 7   b , one or more anti-reflection and/or polarization layers  140  are interposed between the diffuser structure  120  and the substrate  110 &#39;s light incidence plane  112  while, in  FIG. 7   a , the anti-reflection and/or polarization layer  140  is interposed between the collimator stricture  130  and the substrate  110 &#39;s light emission plane  114 . In general, the anti-reflection and/or polarization layer  140  could be arranged anywhere along the path of light before the collimator structure  130 , and is not limited to the two locations as illustrated in  FIGS. 7   a  and  7   b.    
       FIGS. 8   a  and  8   b  are schematic side views showing other variations of the first embodiment of the light control device of the present invention. As shown in  FIG. 8   a , instead of being configured on the light incidence plane  112 , the diffuser structure  120  is configured on the light emission plane  114 , beneath the collimator structure  130 . In  FIG. 8   b , the diffuser structure  120  is implemented as diffractive elements embedded inside the substrate  110 .  
      In addition to the conventional light control functions such as diffusion, collimation, polarization, and anti-reflection, the present embodiment could be extended to include color mixing function when the light source unit comprises assortments of red-light, green-light, and blue-light LEDs to achieve a desired spatial spectral distribution.  FIG. 9  is a schematic view of a portion of the light incident plane where different colored areas are formed by a red-light, a green-light, and a blue-light LED. Please note that in practice a light mixing plate would have already mixed the lights into the white light up to a certain extent but the residual colored lights would still generate similar pattern as shown in  FIG. 9 . As illustrated, the area R has excessive red light while the areas G and B have excessive green and blue lights respectively. On the other hand, the area W has white light while the areas RG, RB, and BG have insufficient blue, green, and red lights, respectively. In other words, for a position (x, y) on the light incidence plane  112  of the light control device, there is a specific spectral profile associated with that position resulted from the colored LEDs used by the light source unit. For example, for a position (x, y) inside the area R, the spectral profile there has a significantly stronger red light than another position inside, say, the area B.  
      To help improving the color mixing, additives of appropriate dyes, pigments, nano/micro particles, phosphors, and/or fluorescent materials could be dispersed in the diffuser structure, collimator structure, or both. In addition, these dyes, pigments, nano/micro particles, phosphors, and/or fluorescent materials could be mixed with adequate resin and coated onto the light control device as a separate coating layer, similar to the polarization or anti-reflection layer shown in  FIGS. 7   a  and  7   b . Despite that the additives are embedded in the spatial distribution of the diffuser structure and/or the collimator structure, the distribution of the additives forms a spatial distribution corresponding to the spatial spectral distribution over an appropriate range of wavelength (or, more specifically, the visible light range) of the incident light to the light control device or to the diffuser structure and/or collimator structure containing the additives. The dyes, pigments, nano/micro particles, phosphors, and/or fluorescent materials change the spatial spectral distribution over the range of wavelength to match that of the desired spatial spectral distribution so that a better color mixing could be achieved by the light control device.  
       FIGS. 12   a ˜ 12   c  are schematic diagrams showing the effects of dyes/pigments, phosphors/fluorescent materials, and nano/micro particles on various spectral profiles respectively. As illustrated in  FIG. 12   a , the spectral profile at a position (x, y) is transformed into a desired spectral profile after the light absorption function provided by appropriate dyes and pigments around the position (x, y), whose characteristic curve over the wavelength is denoted as a dashed line. As shown, the excessive green light (G) is suppressed. On the other hand, in  FIG. 12   b , the insufficient green light is reinforced by the light absorption and remission function provided by appropriate phosphors and fluorescent materials around the position (x, y). Similarly, in  FIG. 12   c , the excessive green light again is suppressed at the position (x, y) as it is scattered by the nano/micro particles around the position (x, y) to other positions.  
      Using  FIG. 9  as an example, appropriate dyes or pigments could be blended into the diffuser structure and/or collimator structure, or the resin of the separate coating layer could cover the areas R and G to absorb the excessive red and green lights. On the other hand, phosphors such as (1) Tris (dibenzoylmethane) Mono (phenanthroline) Europium Complex, or (2) Acetylacetonate Irdium Complex could be added to absorb the excessive UV (ultra violet) and/or blue light and to reemit red light in the area B. Similarly, phosphors such as (1) Coumarin Molecules, or (2) Tris (8-hydroxyquinolinolato) Metal System could be added to absorb the excessive UV and/or blue light and to reemit green light in the area B. Many such pigments, dyes, nano/micro particles, phosphors, and/or fluorescent materials have already been disclosed in the related arts and no further detail is provided here for simplicity sake.  
       FIGS. 10   a ˜ 10   c  are schematic side views showing other embodiments of the light control device according to the present invention. For applications in which only the uniformity of light is required, a second embodiment of the light control device  101  could have no collimator structure, as illustrated in  FIG. 10   a . Please note that, the aforementioned variations to the first embodiment could be adopted by the present embodiment as well, if applicable. For example, the combination of the polarization and/or anti-reflection structures as illustrated in  FIGS. 7   a  and  7   b , and the different implementations of the diffuser structure shown in  FIGS. 8   a  and  8   b  could all be applied to the embodiment shown in  FIG. 10   a . In addition, appropriate dyes, pigments, nano/micro particles, phosphors, and/or fluorescent materials could be added in the diffuser structure or coated as a separate coating layer.  
      Instead of being implemented as a single object, a third embodiment of the light control device  102 , as illustrated in  FIG. 10   b , could be achieved by placing separate light control members together. Here, the term “member” refers to an independent constituent comprising functional structures. In this embodiment, a diffuser member  150  and a collimator member  160  are combined together. In alternative embodiments, it could be another two or more light control members integrated together. The collimator member  160  could be a commercially available conventional prism sheet (or similar brightness enhancement film) having a substantially regular or random distribution of microstructures  162 , or the collimator member  160  could be tailored according to the present invention whose microstructures  162  has a spatial distribution of collimating capability provided by geometric properties and/or refractive indices of the microstructures corresponding to the spatial intensity distribution of the incident light. The diffuser member  150  could be the one shown in  FIG. 10   a , or it could be implemented by having the diffuser structure  120  formed on a film or plate corresponding to the spatial intensity distribution of the incident light. Please note that, the aforementioned variations to the first embodiment could be adopted by the present embodiment as well, if applicable. For example, the combination of the polarization and/or anti-reflection structures as illustrated in  FIGS. 7   a  and  7   b , and the different implementations of the diffuser structure shown in  FIGS. 8   a  and  8   b  could all be applied to the embodiment shown in  FIG. 10   b . In addition, appropriate dyes, pigments, nano/micro particles, phosphors, and/or fluorescent materials could be added in the diffuser member  150  and/or the collimator member  160 , or coated as a separate film or layer.  
      Furthermore, as illustrated in  FIG. 10   c , a fourth embodiment of the light control device  103  is implemented by coating a light control structure to a side of a separate light control member. In this embodiment, a diffuser structure  170  just like the one of the first embodiment in  FIGS. 5   a ˜ 5   e  is coated on a side of the collimator member  160 , which could be a commercial one or one according to the present invention. Again, the aforementioned variations to the collimator structure could be applied here as well. For example, the combination of the polarization and/or anti-reflection structures as illustrated in  FIGS. 7   a  and  7   b  could be applied to the embodiment shown in  FIG. 10   c . In addition, appropriate dyes, pigments, nano/micro particles, phosphors, and/or fluorescent materials could be added in the diffuser structure  170  and/or the collimator member  160 , or coated as a separate coating layer.  
      Using the light control device  100  of  FIG. 5   a  as an example, assuming that the color mixing structure (not shown in  FIG. 5   a ) is implemented as a separate coating layer on the light incident plane  112  and that the light control functions are directly combined, an exemplary manufacturing process of the light control device  100  could be conducted as follows. At first, a camera or a CCD device is used to capture an image of the light source unit (containing the CCFLs  21  and the reflector  12 ). As the light from the light source unit is directly lit on the light incidence plane  112 . The image is used to derive the spatial intensity distribution of the light from the light source unit on the light incidence plane  112 . If the light source unit comprises assortments of red-light, green-light, and blue-light LEDs, the same approach is used to derive the spatial spectral distribution of the light from the light source unit on the light incidence plane  112 . Usually, the spatial spectral distribution is obtained for each primary color. Then, based on the captured images and the derived spatial intensity distribution and spatial spectral distribution, various masks for the diffuser structure, collimator structure, and color mixing structure are developed, for example, using printing screen with photosensitive emulsion coating and light exposing. The substrate  100  is a transparent polymer film or plate substrate typically made of a material such as PET, PEN, PMMA, TAC, Polycarbonate, or the like. Then, an appropriate coating material is coated on the light incidence plane  112  of the substrate  110  using flat plate or roll to roll printing with appropriate mask to obtain the diffuser structure  120  whose degree of haze has a pattern similar to one of  FIGS. 6   a ˜ 6   c . The coating material includes, but is not limited to, UV and/or thermal curable resins which contain particles or additives to scatter the light. Then appropriate dyes, pigments, nano/micro particles, phosphors, and/or fluorescent materials are blended into a proper resin and are coated also using flat plate or roll to roll printing with appropriate masks. The diffuser structure  120  and the color mixing coating layer are then solidified by thermal or ultra-violet (UV) curing. A mold for the microstructures  132  of the collimator structure  130  is prepared by machinery, lithographic, or MEMS methods. Then, resins having high refractive indices, preferably in the range of 1.55˜1.75, are coated on the light emission plane  114  of the substrate  110  using flexography or micro gravure methods. The microstructures  132  of the collimator structure  130  are then formed by embossment with UV/thermal curing.  
      To achieve a diffuser structure  120  whose pattern is similar to the one illustrated in  FIG. 6   d , a number of approaches could be adopted. One such approach is illustrated in  FIG. 11   a , in which layers of coating materials  121  and  122 , each having identical or different degrees of haze, are sequentially formed on the light incidence plane  112  with successive printing processes and appropriate masks.  FIG. 11   b  illustrates another approach, in which coating materials  123  and  124  having specific degrees of haze are printed on specific areas of the light incidence plane  112  in order to obtain a pattern of  FIG. 6   d . Similarly, a flexogravure printing process could be conducted to obtain continuously changing degree of haze, as illustrated in  FIG. 6   e.    
      To explain how interactive combination is achieved, the collimating function of the light control device  100  in the previous example is assumed to be interactively combined with its preceding diffusing function. In this scenario, the diffuser structure  120  and the color mixing structure (not shown) could be formed using identical means as outlined in the previous example. Then, the semi-finished light control device  100  (i.e., with the diffuser structure and color mixing structure formed) is placed in front of the light source unit. The camera or CCD device is used again to capture an image of the light emission plane  114  of the light control device  100 . The image is then used to derive the spatial intensity distribution of the light from the light source unit on the light emission plane  114 . After this is done and appropriate masks are developed, the same manufacturing process could be adopted to form the collimator structure  130  as outlined in the previous example.  
      Please note that computer simulation would play a vital role in the manufacturing process of the present invention, especially when multiple light control functions are directly or interactively combined together and the performance of the light control device is jointly determined by these inter-related light control functions. In order to obtain an optimal configuration of these light control functions, computer simulation could save tremendous amount of trial-and-error effort. For example, a manufacturer only needs to capture images of a light source unit and the derivation of the spatial intensity distribution and the spatial spectral distribution for each of the combined light control functions could be conducted entirely in a laboratory before really going on-line for mass production.  
      To illustrate the effect of the present invention, a number of simulations are conducted based on the light source unit of  FIG. 2   a  in a closed system where scattered light is confined for recycling. For one simulation, a light control device is as illustrated in  FIG. 2   c  is used, in which its diffuser structure has a pattern similar to  FIG. 6   c  with an 80% degree of haze, and its collimator structure has a pattern similar to  FIG. 5   b . In the simulation, the illuminance (Lux) of the positions on a 50 mm×50 mm surface is obtained after the light from the light source unit of  FIG. 2   a  has passed through the light control device, as shown in  FIG. 2   d . In comparison, another simulation is conducted using a conventional brightness enhancement or prism film with regularly distributed prism structures on one side and no diffuser structure on the other side of the film. The illuminance of the positions on a 50 mm×50 mm surface is obtained after the light from the light source unit has passed through the conventional prism film, as shown in  FIG. 2   b . As can be seen from  FIGS. 2   b  and  2   d , the uniformity of the emitted light of the present invention is superior.  
      The spatial area of the 50 mm×50 mm surface is divided into 20×20 grids, and the maximum, minimum, and average fluxes of illuminance are obtained from the middle 18×18 grids for the three simulations of  FIGS. 2   a  (i.e., no light control device),  2   b  (i.e., using conventional brightness film), and  2   d  (i.e., using the present invention), respectively, and summarized in the following Table 1. In Table 1, the uniformity U is calculated as the ratio of the minimum and average illuminance (Glare and Uniformity in Road Lighting Installations, Publication CIE 31-1976.). Please note that the average flux can be used to represent the light power in the system. As shown, the uniformity is significantly improved from 46% to 75% after light passing through the light control device of the present invention, sacrificing only 24% of power, while the conventional prism film can only achieve 62% of uniformity with 13% of energy loss. In order for the conventional prism film to achieve the same level of uniformity, a diffuser structure is needed and considerably additional 20˜30% energy loss would happen. Moreover, if additional light control devices are used together as shown in  FIG. 4   e , highly uniform light can be easily achieved.  
                                   TABLE 1                                   Min.   Max.   Average               (Lux)   (Lux)   (Lux)   U                                                        No light control device   5535.86   25225.41   11966.55   46%       Conventional prism film   6525.12   16217.53   10480.43   62%       The present invention   6791.19   12673.98   9045.51   75%                  
 
      In addition, the present invention could provide the following advantages. At first, if used in a backlight unit for a LCD, the cost of the backlight unit could be significantly reduced as the light guide plate, diffusion sheet, prism sheet could be omitted. Secondly, the light utilization efficiency is increased as component and material usage are reduced and therefore excessive absorption or scattering loss are prevented. Thirdly, the light control device could be fabricated using conventional processes such as roll to roll printing, silkscreen printing, lithographic, and ink-jet printing processes.  
      Please note that the present invention could be applied in a reversed manner in that a light source unit has its CCFLs or LEDs arranged in a pattern corresponding to the specific distribution of haze of a diffusion sheet or plate, or to the specific distribution of the refractive indices and/or geometric properties of a prism sheet, or to the specific distribution of the color mixing additives of a color mixing film, instead of the other way around as described in this specification. This type of approaches should be considered to be within the scope of the present invention.  
      Although the present invention has been described with reference to the preferred embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.