Patent Publication Number: US-2007097291-A1

Title: Polymer dispersed liquid crystal

Description:
BACKGROUND  
      Many displays attenuate visible light with liquid crystals or with polymer dispersed liquid crystals. Displays using liquid crystals suffer from viewing degradation, light loss and pressure sensitivity. Displays using polymer dispersed liquid crystals may have relatively low contrast ratios. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic illustration of an embodiment of a display according to one example embodiment.  
       FIG. 2  is a graph illustrating Polymer Dispersed Liquid Crystal (PDLC) transmittance over a range of different wavelengths as a function of applied voltage according to one example embodiment.  
       FIG. 3  is a graph illustrating PDLC transmittance of electromagnetic wavelengths at a zero applied voltage according to one example embodiment.  
       FIG. 4  is an exploded perspective view schematically illustrating another embodiment of the display of  FIG. 1  according to an example embodiment.  
       FIG. 5  is an enlarged fragmentary plan view of an electrode matrix of the display of  FIG. 4  according to an example embodiment.  
       FIG. 6  is an enlarged view of the electrode matrix of  FIG. 5  taken along line  6 - 6  according to an example embodiment.  
       FIG. 7  is a fragmentary sectional view of an assembled portion of the display of  FIG. 4  according to an example embodiment.  
       FIG. 8  is an enlarged fragmentary plan view of a PDLC matrix of the display of  FIG. 4  according to an example embodiment.  
       FIG. 9  is an enlarged fragmentary plan view of a photo luminescent matrix of the display of  FIG. 4  according to an example embodiment.  
       FIG. 10  is a fragmentary sectional view of a portion of another embodiment of the display of  FIG. 1  according to an example embodiment. 
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS  
       FIG. 1  schematically illustrates display system  10  which generally includes near-UV light source  14 , modulator  18 , photo luminescent structure  28 , voltage source  30  and controller  32 . Near-UV light source  14  comprises a source of near-UV light. For purposes of this disclosure, the term “near-UV light” shall mean a light or electromagnetic energy having wavelengths of between about 360 nm and about 420 nm. According to one embodiment, source  14  is configured to emit a portion of the electromagnetic spectrum including wavelengths of between about 360 nanometers and about 500 nanometers and nominally between about 370 nanometers and 410 nanometers. In one embodiment, source  14  may comprise light-emitting diodes. In another embodiment, light source  14  may comprise tubes or other sources for near-UV light. According to one embodiment, near-UV light source  14  includes InGaN light emitting diodes configured to emit near-UV light at a wavelength of about 400 nanometers.  
      Photo luminescent structure  28  comprises one or more layers of one or more photo luminescent materials which are configured to emit a second portion of the electromagnetic spectrum, such as visual light, in response to being impinged by near-UV light from source  14 . In one embodiment, photo luminescent structure  28  compromises a color change material such as one or more color phosphors. For example, in one embodiment, photo luminescent structure  28  may be configured to down convert UV light into light having wavelength within a visible spectrum such as red, green and blue. According to one embodiment, photo luminescent structure  28  may be formed from a perylene-based organic color change material which provides saturated color emission, high fluorescence quantum efficiency and acceptable “light-fastness.” In one embodiment, photo luminescent structure  28  comprises L-184 supplied by BEAVER LUMINESCERS.  
      Modulator  18  comprises a mechanism located between source  14  and photo luminescent structure  28  that is configured to selectively attenuate or shutter light from source  14 . Modulator  18  actuates between different transmissive states based upon voltage applied by voltage source  30  as controlled by controller  32 . Modulator  18  generally includes conductors  20 ,  22  and polymer dispersed liquid crystal (PDLC)  24 . Conductors  20  and  22  comprise one or more layers of transparent electrically conductive material between which is sandwiched PDLC  24 . Conductors  20  and  22  are configured to be connected to voltage source  30  so as to create an electrical field across PDLC  24  to actuate PDLC  24  to different light transmissive states. According to one embodiment, conductors  20  and  22  may be formed from a transparent electrically conductive material such as indium tin oxide. In other embodiments, conductors  20  and  22  may be formed from other transparent or translucent electrically conductive materials.  
      PDLC  24  comprises a layer of polymer dispersed liquid crystal material sandwiched between conductors  20  and  22 . PDLC  24  is configured to selectively block or attenuate light based upon the electric field present across PDLC  24 . PDLC  24  is configured to attenuate light or electromagnetic radiation having a wavelength of less than or equal to about 480 nanometers at a higher rate as compared to electromagnetic radiation having wavelengths greater than 500 nanometers. PDLC  24  is configured to absorb light from light source  14  having wavelengths of less than or equal to about 500 nanometers. In one embodiment, PDLC  24  includes liquid crystal droplets having individual diameters of less than or equal to about 800 nanometers. In other embodiments, PDLC  24  includes liquid crystal droplets having individual diameters of less than or equal to about 500 nanometers. The reduced diameters of the liquid crystal droplets enhances absorption of PDLC  24  of near-UV light. This enhanced absorption may enable PDLC  24  to provide display system  10  with greater contrast.  
      According to one example embodiment, PDLC  24  is formed by combining a pre-polymer and liquid crystals to form a mixture followed by the addition of a polymerization agent and curing the mixture to form liquid crystal droplets having a diameter of less than or equal to about 800 nanometers. In particular, according to one example embodiment, a liquid crystal and a pre-polymer are mixed in a desired ratio by stirring at room temperature until homogenous.  
      In one embodiment, the pre-polymer includes a mixture of a photo activator and a monomer. According to one example embodiment, the photo activator may comprise 10.5% by weight MXM035 part A, commercially available from Merck Specialty Chemicals Ltd, South Hampton, England. In such an embodiment, the monomer may comprise 89.5% by weight MXM035 part B, commercially available from Merck Specialty Chemicals Ltd., South Hampton, England. According to one embodiment, this pre-polymer is subsequently mixed with liquid crystal to a point of saturation. In one example embodiment, the liquid crystal may comprise BL035, commercially available from Merck Specialty Chemicals Ltd., South Hampton, England. The pre-polymer and the liquid crystal are mixed such that the liquid crystal has a weight percentage of the resulting pre-polymer/liquid crystal mixture of at least about 55%. In one embodiment, the liquid crystal such as BL035, is mixed with the pre-polymer (MXM035 parts A and B) to substantially complete saturation at room temperature (20° C.) of about 60% by weight. In some embodiments, the solubility of the liquid crystal in the pre-polymer is increased to above 60% by weight by additional methods such as by heating the pre-polymer to above 20° C. The resulting mixture is stirred until substantially clear.  
      Upon completion of preparation of the mixture, the mixture is spread to a thickness of between about 2 micrometers and 20 micrometers. In one embodiment, the mixture of the pre-polymer and liquid crystal is dispensed into a suitable cell by capillary action. The cell may be formed from glass coated with a material such as indium tin oxide, wherein the cell gaps are between 2 microns and 20 microns. Alternatively, the liquid crystal/pre-polymer mixture may be coated onto a substrate such as indium tin oxide coated glass or plastic or other techniques such as bar or doctor blade coating.  
      Once the liquid crystal/pre-polymer mixture has been spread to a thickness of between 2 microns and about 20 microns, the mixture is subsequently cured by exposing the mixture to ultraviolet light. According to one embodiment, curing is performed under conditions of controlled temperature and UV power. In one embodiment, curing is performed in a range of 22 to 30 degrees C. with a lamp intensity at a substrate of at least about 1.5 W/cm 2  and less than or equal to about 5.5 W/cm 2  at a UV wavelength of 315 to 400 nanometers for a time of between about 1 and about 3 seconds. According to one embodiment, a post cure at lower lamp power may be performed to provide for full cure. In one embodiment, the process is complete when the mixture is no longer transitioning from a nematic liquid crystal phase to an isotropic liquid crystal phase. Although the example PDLC  24  has been described as being formed according to the above described process, PDLC  24  may alternatively be formed using other materials, other mixtures or proportions, other curing rates, and in other fashions.  
      In one embodiment, coating of the liquid crystal/pre-polymer mixture may be upon an open substrate. In such an embodiment, curing of the mixture is performed in an inert atmosphere to inhibit atmospheric oxygen. A second substrate including conductor  46  and conductor  48  may be subsequently laminated to the film resulting from curing of the mixture.  
       FIGS. 2 and 3  are graphs illustrating spectral transmission response of one embodiment of PDLC  24 , as formed according to the above process, at various voltages. In the particular example illustrated, a DC voltage is applied. In other embodiments, a AC voltage may alternatively be used. As shown by the graph in  FIG. 2 , PDLC  24  strongly attenuates light having a wavelength of about 525 nanometers when a zero voltage is applied. As shown by the graph of  FIG. 2 , even with an applied voltage of 15 volts, PDLC strongly attenuates light having a wavelength of less than about 450 nanometers. As shown by the graph in  FIG. 3 , when a zero voltage is applied across PDLC  24 , PDLC  24  strongly attenuates light having a wavelength of less than about 400 nanometers. As a result, PDLC  24  may achieve a relatively high percentage transmittance with an applied voltage and a relatively low transmittance in the absence or lessening of the applied voltage. The ratio of the transmittance under a voltage as compared to transmittance without a voltage or with a lessened voltage is sometimes referred to as contrast. As shown by  FIG. 3 , PDLC  24  will attenuate a 370 nanometer light at an off-state or zero voltage such that about 0.035% of such light passes through PDLC  24 . As shown by  FIG. 2 , PDLC  24  will exhibit a transmittance of 20% when 35 volts are applied across PDLC  24 , resulting in a contrast ratio of 570:1. PDLC  24  will exhibit a transmittance of 40% when 65 volts are applied across PDLC  24 , resulting in a contrast ratio of 1140:1.  
      As shown by  FIG. 3 , for light having a wavelength of 400 nanometers, PDLC  24  exhibits a 0.05% transmittance when in an off-state (i.e., zero volts are applied across PDLC  24 ). As shown by  FIG. 2 , having a wavelength of 400 nanometers, PDLC  24  exhibits a transmittance of about 20% upon application of 30 volts, resulting in a contrast ratio of 400:1. Simple contrast ratio is defined as maximum transmission/minimum transmission. As further shown by the graph of  FIG. 2 , for light having a wavelength of 400 nanometers, PDLC  24  exhibits a transmittance of about 40% in response to 40 volts being applied across PDLC  24 , resulting in a contrast ratio of 800:1. As shown by the graphs in  FIGS. 2 and 3 , the particular example of PDLC  24  facilitates high contrast ratios at relatively low voltages.  
      As shown by  FIG. 1 , voltage source  30  is electrically connected to conductors  20  and  22 . Voltage source  30  is configured to selectively apply a voltage to one or both of conductors  20  and  22  to selectively vary the transmittance of PDLC  24 . Controller  32  comprises a processing unit configured to generate control signals for directing voltage source  30  to selectively apply conductors  20  and  22  to vary the transmittance of PDLC  24 . For purposes of disclosure, the term “processing unit” shall mean a presently available or future developed processing unit that executes sequences of instructions contained in a memory. Execution of the sequences of instructions causes the processing unit to perform steps such as generating control signals. The instructions may be loaded in a random access memory (RAM) for execution by the processing unit from a read only memory (ROM), a mass storage device, or some other persistent storage. In other embodiments, hard wired circuitry may be used in place of or in combination with software instructions to implement the functions described. Controller  32  is not limited to any specific combination of hardware circuitry and software, nor to any particular source for the instructions executed by the processing unit. In the particular example illustrated, controller  32  is further configured to generate control signals directing the operation of light source  14 .  
      In operation, light source  14  emits a portion of the electromagnetic spectrum. In the particular example shown, light source  14  emits light having wavelengths of between about 370 and 400 nanometers. Controller  32  generates control signals directing voltage source  30  to create a voltage across PDLC  24  to actuate PDLC  24  between various levels of transmittance depending upon a desired intensity to be emitted by display system  10 . When zero volts is applied across PDLC  24 , PDLC  24  substantially attenuates the light from light source  14  prior to such light reaching photo luminescent structure  28 . As a result, photo luminescent structure  28  emits little if any light and display system  10  is substantially dark. When controller  32  generates control signals directing voltage source  30  to create a voltage across PDLC  24 , PDLC  24  exhibits a higher transmittance such that light from light source  14  passes through PDLC  24  to photo luminescent structure  28 . As a result, photo luminescent structure  28  emits a second portion of the electromagnetic spectrum, such as visible light, resulting in display system  10  also emitting visible light. In particular embodiments, photo luminescent structure  28  may be configured to emit selected wavelengths or colors of light upon being impinged by light from light source  14 . In particular embodiments, display system  10  may include a multitude of modulator pixels or cells such as modulator  18  and may also include a corresponding multitude of photo luminescent pixels or cells.  
       FIG. 4  is an exploded perspective view of display  110 , another embodiment of display system  10  shown and described with respect to  FIG. 1 . Display  110  generally includes a UV-light source  114 , diffuser  116 , modulator  118 , which includes electrode matrix  120 , electrode  122  and PDLC matrix  124 , photo luminescent matrix  128 , protective film  134 , and frame  136 . Light source  114  comprises a device configured to emit near-UV light in a direction towards photo luminescent matrix  128 . In the particular example illustrated, light source  114  includes ultraviolet light-emitting tubes  140  secured to a support  142  which is bound by a frame  144 . In other embodiments, light source  114  may alternatively include tubes configured to emit light having wavelengths proximate to the ultraviolet wavelengths. In still other embodiments, light source  114  may alternatively include light emitting diodes configured to emit near-UV light.  
      Diffuser  116  comprises a sheet or layer of translucent material configured to diffuse light emitted by light source  114  to distribute the light across the display. In particular embodiments, a second panel (not shown) (from NITTO DENKO Group, OPTMATE Corp as an example) may be provided which collimates the light so that it enters normal to the surface plane of the display. In the particular embodiment shown, diffuser  116  comprises a translucent plastic such as Illuminex diffuser film commercially available from GE Advanced Materials. In other embodiments, diffuser  116  may comprise other materials or may be omitted.  
      Electrode matrix  120  comprises an assembly including a plurality of independently or selectively chargeable electrodes  150  (schematically shown in  FIG. 4 ). Electrodes  150  are configured to be independently charged to distinct voltages and cooperate with electrode  122  to selectively actuate distinct portions of PDLC matrix  124  between different transmissive states.  FIGS. 5 and 6  illustrate face  152  of electrode matrix  120  in greater detail.  FIG. 7  is a sectional view illustrating matrix  120  in greater detail, as well illustrating electrode  122 , matrix  124 , matrix  128  and film  134  as assembled. As shown by  FIGS. 5-7 , in addition to electrodes  150 , electrode matrix  120  includes substrate  156 , data lines  158 , signal lines  160  and switching devices  162 . Electrodes  150  comprise platelets or panels of transparent electrically conductive material, such as indium tin oxide, arranged across face  152 . Electrodes  150  are electrically separated or partitioned from one another by dielectric breaks  163  (shown in  FIG. 7 ). In the particular example illustrated, breaks  163  comprise portions of dielectric material, such as silicon, extending around and between electrodes  150 . Breaks  163  are omitted in  FIGS. 5 and 6  for purposes of illustrating lines  158  and  160 . In other embodiments, breaks  163  may comprise gaps between electrodes  150 . Although, in the particular embodiment illustrated, electrodes  150  are illustrated as having a square geometry and as being arranged in a series of linearly arranged rows and columns, electrodes  150  may alternatively have other shapes or other surface geometries and may be arranged in other orders or relative positions along face  152 . In other embodiments, electrodes  150  may be formed from other transparent electrically conducted materials.  
      Substrate  156  comprises one or more layers of transparent dielectric material configured to support electrodes  150 , data lines  158 , signals lines and switching devices  162 . In one embodiment, substrate  156  may comprise glass. In another embodiment, substrate  156  may comprise one or more layers of a polymeric or plastic material.  
      Data lines  158  comprise electrically conductive lines or traces of one or more electrically conductive materials carried or formed upon substrate  156 . In other embodiments, lines  158  may be formed within the material or materials of breaks  163 . Data lines  158  are electrically connected to a voltage source, such as voltage source  30  shown and described with respect to  FIG. 1 , and are selectively connectable to each of electrodes  150  by switching devices  162 . Data lines  158  supply charge to electrodes  150  to establish a voltage across PDLC matrix  124  as will be described hereafter.  
      Signal lines  160  comprise electrically conductive lines or traces carried or formed upon substrate  156 . In other embodiments, lines  160  may be formed within the material or materials of breaks  163 . Signal lines  160  are configured to be selectively connected to a voltage source, such as voltage source  30  shown and described with respect to  FIG. 1 , by a controller, such as controller  32 . Signal lines  160  are further electrically connected to switching device  162 . Signal lines  160  are configured to apply a charge to switching device  162  so as to actuate switching device  162  between a first electrically conductive state in which charge from data line  158  is transmitted to electrode  150  and a second open state in which charge from data line  158  is not transmitted to electrode  150 .  
      Switching devices  162  comprise devices configured to selectively transmit charge from data lines  158  to electrodes  150  based upon signal voltages received via signal lines  160 . In the particular example illustrated in  FIG. 6 , switching devices  162  each comprise a thin film transistor arrangement including a source electrode  164  electrically connected to data line  158 , a drain electrode  166  electrically connected to electrode  150 , a gate electrode  168  (shown in hidden lines) electrically connected to signal line  160  and a semiconductive material  170  interposed between source electrode  164 , drain electrode  166  and gate electrode  168 . In other embodiments, switching device  162  may comprise a metal-insulator-metal device or other switching devices. In still other embodiments, in lieu of including an active matrix control arrangement, electrode matrix  120  may alternatively include a passive control arrangement for each of electrodes  150 , wherein switching devices for actuating electrodes  150  between different voltage levels are grouped together along a perimeter or at another location outside of electrode matrix  120 .  
      Electrode  122  generally comprises one or more continuous layers or sheets of transparent electrically conductive material extending opposite to electrode matrix  120  with PDLC matrix  124  therebetween. Electrode  122  cooperates with electrodes  150  of electrode matrix  120  to create a voltage across PDLC matrix  124  to actuate portions of PDLC matrix  124  between different transmissive states. In one particular embodiment, electrode  122  is electrically connected to ground. In other embodiments, electrode  122  may be charged. In one embodiment, electrode  122  is formed from an electrically conductive material such as indium tin oxide. In other embodiments, electrode  122  may be formed from other transparent electrically conductive materials.  
      PDLC matrix  124  is sandwiched between electrode matrix  120  and electrode  122 . As shown by  FIGS. 7 and 8 , PDLC matrix  124  generally includes grid  180  and PDLC  182 . Grid  180  comprises a series of dielectric near-UV light absorbing walls which substantially partition PDLC  182  into a plurality of cells or pixels  184 . As shown by  FIG. 7 , such cells or pixels  184  are generally aligned with corresponding electrodes  150  of electrode matrix  120 . In particular, the walls of grid  180  are aligned with and extend opposite to the dielectric breaks  163  separating electrodes  150 . The walls of grid  180  attenuate the transmission of near-UV light passing through PDLC  182  in one cell  184 , that has been actuated to a transmissive state, into an adjacent cell  184  containing PDLC  182  which is intended to be in a lesser transmissive state. In other words, grid  180  reduces visual cross talk between portions of PDLC  182  that are in different transmissive states due to different applied voltages by their respective electrodes  150 . In the particular example shown in which grid  180  also extends opposite to dielectric breaks  163  between electrodes  150 , grid  180  also serves to hide or block data lines  158 , signal lines  160  and switching devices  162  (shown in  FIG. 6 ). Although grid  180  is illustrated as forming rectangular or square cells  184 , wherein each cell has substantially the same dimensions, grid  180  may alternatively be configured to form cells  184  having other shapes and cells  184  having different uniform or non-uniform dimensions.  
      In the particular example illustrated, grid  180  comprises a screen-like panel formed from a flexible dielectric material such as black anodized aluminum. In other embodiments, grid  180  may alternatively be formed from other dielectric light absorbing materials such as black polymers. In the particular example illustrated, grid  180  has a substantially uniform depth across its length and width. The depth is at least 2 microns, less than or equal to about 20 microns and nominally about 8 microns. In other embodiments, grid  180  may have other dimensions. In some embodiments, grid  180  may be omitted.  
      PDLC  182  comprises a polymer dispersed liquid crystal material having liquid crystal droplets  185  to disperse throughout a polymer  186 . Such liquid crystal droplets have a diameter of less than or equal to about 800 nanometers and nominally less than or equal to about 500 nanometers. In one embodiment, PDLC  182  may be formed according to the above-described procedure as set forth with respect to PDLC  24 .  
      According to one embodiment, grid  180  is formed within PDLC  182  prior to the curing of the pre-polymer/liquid crystal mixture. In one embodiment, grid  180  is immersed within a layer of liquid pre-polymer/liquid crystal mixture. The mixture encapsulating grid  180  is subsequently cured at a rate such that the liquid crystal forms droplets having individual diameters less than or equal to about 800 nanometers and nominally less than or equal to about 500 nanometers. This process enables cells  184  or grid  180  to be quickly filled with the mixture that forms PDLC  182  upon being cured. This process may result in PDLC  182  continuously extending from one cell  184  to an adjacent cell  184  across grid  180 . In other embodiments, the pre-polymer/liquid crystal mixture may be applied across grid  180 . In still other embodiments, cells  184  may be individually or collectively filled with the pre-polymer/liquid crystal mixture prior to curing without the mixture flowing over or extending above the walls of grid  180 . In still other embodiments, PDLC  182  may be deposited within cells  184  after the initial pre-polymer/liquid crystal mixture is cured.  
      As shown by  FIG. 4 , photo luminescent matrix  128  includes a plurality of pixels  190  (schematically shown in  FIG. 4 ) of photo luminescent material across and opposite to cells  184  containing a PDLC  182 . In other embodiments, pixels  190  may be formed from a photo luminescent material such as a perylene-based organic color change material. In other embodiments, pixels  190  may be formed from other photo luminescent materials, color change materials or wavelength downconverters.  
      As shown by  FIGS. 7 and 9 , in the example illustrated, pixels  190  are configured to emit different portions of the electromagnetic spectrum such as different wavelengths of light or different colors as compared to one another upon being impinged or irradiated by near-UV light that has been transmitted through PDLC matrix  124 . In the particular example shown, pixels  190  include pixels  192  of photo luminescent material configured to emit red light upon being irradiated by near-UV light, pixels  194  are configured to emit green light upon being irradiated by near-UV light and pixels  196  are configured to emit blue light upon being irradiated by near-UV light. As shown by  FIG. 9 , pixels  192 ,  194  and  196  are arranged in an off-set pattern relative to one another such that a first pixel configured to emit a particular color is not located side-by-side another pixel configured to emit the same color. This pattern facilitates selective activation of pixels  192 , 194  and  196  to provide a multi-colored display. In other embodiments, pixels  192 ,  194  and  196  may have other patterns or may be configured to emit other colors of light.  
      As shown by  FIG. 7 , pixels  190  are formed by patterning photo luminescent materials upon a transparent dielectric substrate  198 . In the particular example illustrated, substrate  198  may comprise a panel or sheet of glass. In another embodiment, substrate  198  may comprise a panel or sheet of other transparent dielectric material such as a transparent polymer material. As shown by  FIG. 4 , in one embodiment, substrate  198  may also serve as a substrate upon which electrode  122  is formed. According to one embodiment, substrate  198  has a thickness of about 2 mm to space pixels  190  from cells  184  and PDLC  182 . In other embodiments, substrate  198  and electrode  122  may have other thicknesses to space pixels  190  from PDLC  182 . In still other embodiments, substrate  198  may be omitted, wherein pixels  190  are patterned directly upon electrode  122  or wherein pixels  190  are patterned upon another structure such as film  134  (shown in  FIG. 4 ).  
      As shown by  FIG. 7 , each of pixels  190  extends opposite to and generally corresponds to an individual cell  184  containing PDLC  182 , wherein the cells  184  of PDLC  182  extend opposite and correspond to individual electrodes  150 . In the particular embodiment illustrated, each of pixels  190  has a surface area of at least 2 um×6 um, of less than or equal to 1 mm×3 mm and nominally about 100 um×300 um. In the particular embodiment illustrated, each of pixels  190  as a shape and dimension corresponding to shapes and dimensions of cells  184  of grid  180  and electrodes  150 . In other embodiments, pixels  190  may have shapes or dimensions differing from that of cells  184  or electrodes  150 . Although pixels  190  are illustrated as having a square geometry and as being arranged in rows and columns, pixels  190  may alternatively have other surface geometries and may have other arrangements.  
      In operation, a controller such as controller  32  (shown and described with respect to  FIG. 1 ) generates control signals directing a voltage source, such as voltage source  30  (shown and described with respect to  FIG. 1 ) to transmit a voltage along data lines  158  (shown in  FIG. 6 ) and to selectively transmit voltage along signal lines  160  (shown in  FIG. 6 ) to selectively actuate switching devices  162  (shown in  FIG. 6 ) between open and closed states to selectively charge individual electrodes  150 . Those electrodes  150  which are charged establish a voltage or electric field across their respective cells  184  containing PDLC  182 . As a result, the PDLC  182  in such cells  184  exhibits increased transmittance such that near-UV light emitted by light source  114  passes through such cells  184  and impinges upon corresponding opposite pixels  190 . At the same time, those electrodes  150  which are not charged as a result of switching devices  162  remaining in an open state do not apply an electric field across PDLC  182  of their respective opposite cells  184  or create a lesser electric field such that the PDLC  182  within such cells  184  has a lower transmittance. As a result, the PDLC  182  in which a lesser electric field is applied, attenuates near-UV light from light source  114  to a greater extent. Consequently, pixels  190  aligned and generally opposite to those cells  184  containing light attenuating PDLC  182  are irradiated with less near-UV light and emit a lower intensity of light or no light. By selectively charging electrodes  150 , the controller, such as controller  32 , shown in  FIG. 1 , may selectively cause pixels  192 ,  194  and  196  to be irradiated by different levels of near-UV light such that such pixels  192 ,  194  and  196  emit different intensities of red, green and blue light, respectively, to produce a desired color image or display.  
      Film  134  comprises one or more layers of translucent material configured to overlie and protect photo luminescent pixels  190  of photo luminescent matrix  128 . In particular embodiments, film  134  may additionally include other optical materials configured to enhance light emitted by display  110 . Frame  136  comprises a structure configured to cooperate with frame  144  so as to rigidify and secure intermediate components of display  110  and to potentially facilitate mounting of display  110  to other structures. In particular embodiments, film  134  and frame  136  may be omitted or may have other configurations.  
      Overall, display  110  provides a display image that exhibits relatively high levels of brightness and high levels of contrast. Display  110  provides an emissive type display and operates at relative low voltages and with relatively fast response times. At the same time, display system  10  may be configured so as to be flexible, facilitating display system  10  for use in touch screen applications.  
       FIG. 10  is a sectional view schematically illustrating display system  210 , another embodiment of display system  10 . Display system  210  is similar to display system  110  (shown and described with respect to  FIGS. 4-9 ) except that display system  210  includes a stack of shutters or modulators  246 A,  246 B,  246 C and  246 D (collectively referred to as modulators  246 ) in lieu of a single modulator  146  as shown in  FIG. 7 . Those remaining components of display system  210  correspond to the components of display system  110 . For example, display system  210  also includes substrate  198 , photo luminescent matrix  128  and film  134  (shown and described with respect to display system  110 ). Although not illustrated in  FIG. 10 , display system  210  additionally includes light source  114 , diffuser  116  and frame  136  (shown and described with respect to  FIG. 4 ). Modulators  246  are each configured to selectively attenuate near-UV light emitted by light source  114  (shown in  FIG. 4 ) prior to such near-UV irradiating pixels  190  of photo luminescent matrix  128 . Modulators  246  are each substantially similar to modulator  146  (shown and described in  FIG. 7  with respect to display  110 ). In particular, each modulator  246  includes electrode matrix  120 , electrode  122  and PDLC matrix  124 . As noted with respect to display  110 , in some embodiments, PDLC matrix  124  may omit grid  180 .  
      Modulators  246  cooperate with one another to selectively attenuate light and to selectively permit transmission of near-UV light from light source  114  (shown in  FIG. 4 ) to pixels  190  of photo luminescent matrix  128 . Because modulators  246  are stacked, the individual thicknesses of PDLC matrix  124  of each of modulators  246  may be reduced while maintaining the total or collective thickness of PDLC  182  between light source  114  (shown in  FIG. 4 ) and photo luminescent matrix  128 . By reducing the thickness of each individual PDLC matrix  124 , electrodes  150  may be more closely spaced to electrodes  122  of each modulator  246 . This reduced spacing between electrodes  150  and  122  of each modulator  246  may reduce the operating voltages used to actuate PDLC  182  between different transmittance states while substantially maintaining or reducing by a relatively small amount the responsiveness of cells  184  containing PDLC  182  to actuate between different transmittance states. By maintaining the overall or collective thickness of PDLC  182 , the collectively ability of modulators  246  to attenuate near-UV light prior to such light irradiating photo luminescent matrix  128  is also maintained or reduced by a relatively small amount as compared to a single photo luminescent matrix  124  having the same thickness. As a result, the contrast of display  210  is substantially maintained.  
      According to one example embodiment, each PDLC matrix  124  of modulators  246  (A-D) has a thickness of less than or equal to about  2  microns. In other embodiments, each PDLC matrix  124  may have greater thicknesses or reduced thicknesses. Although display  210  is illustrated as including four stacked modulators  246 , display system  10  may alternatively include a greater or fewer number of such stacked modulators.  
      According to one embodiment, aligned electrodes  150  of modulators  246  are electrically connected to a voltage source so as to be substantially charged to the same voltage such that PDLC  182  in aligned cells  184  of modulators  246  all exhibit the same transmittance as one another. In other embodiments, electrodes  150  of modulators  246  that are aligned with one another may alternatively be electrically connected to a voltage source and a controller, such as controller to alternatively independently charge electrodes  150  to distinct voltages as compared to one another. By varying the charge applied to different aligned electrodes  150 , the controller of display  210  may adjust and control the extent to which near-UV light is attenuated by the aligned set of electrodes  150  so as to also adjust and control the extent to which the aligned pixel  190  is irradiated by the near-UV light and the intensity of the light emitted by the particular pixel  190 .  
      Although the present disclosure has been described with reference to example embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the claimed subject matter. For example, although different example embodiments may have been described as including one or more features providing one or more benefits, it is contemplated that the described features may be interchanged with one another or alternatively be combined with one another in the described example embodiments or in other alternative embodiments. Because the technology of the present disclosure is relatively complex, not all changes in the technology are foreseeable. The present disclosure described with reference to the example embodiments and set forth in the following claims is manifestly intended to be as broad as possible. For example, unless specifically otherwise noted, the claims reciting a single particular element also encompass a plurality of such particular elements.