Abstract:
A display includes a light switch overlying a backlight and having at least two light shutters which do not, by themselves, convey information by the shape thereof. The lit area of the backlight is equal to or greater than the sum of the areas of the shutters within the area. The display can also include a graphics layer overlying the light switch. The information content of the display is changed by changing the graphics layer.

Description:
FIELD OF THE INVENTION 
     This invention relates to displays and, in particular, to a display having a plurality of light shutters, each of which is a substantial fraction of the total display and which, in themselves, do not display information but improve the intelligibility of the information that is displayed. 
     GLOSSARY 
     As used herein, a “display” is a device that provides information in visual form to a viewer. 
     A “graphic” can be text, a symbol, an arbitrary shape, or some combination thereof. A graphic can be translucent, diffuse, shaded, colored, a silhouette or outline, or some combination thereof. Graphics can be positive (black on white) or negative (white on black), where white is diffuse, shaded, etc. 
     A “pixel” is a picture element within a single boundary. 
     An “EL lamp” is a thick film, capacitive device including a layer containing electroluminescent phosphor between two electrodes. The phosphor is luminous when a voltage is applied to the electrodes. 
     A “thick film” EL lamp refers to one type of EL lamp and “thin film” EL lamp refers to a different type of EL lamp. The terms only broadly relate to actual thickness and actually identify distinct disciplines. A thin, thick film EL lamp is not a contradiction in terms and such a lamp is considerably thicker than a thin film EL lamp. 
     “Opaque” does not mean that no light is transmitted, only that the amount of light transmitted is substantially reduced, e.g. to ten percent of incident light. 
     A “phosphor” is not restricted to a single type of phosphor or dopant and does not exclude cascading phosphors or dyes for color enhancement. 
     “Overlying” or “underlying” do not imply orientation and merely describe a situation wherein layers of materials have major surfaces facing each other, with or without contact. The surfaces are not necessarily planar. 
     BACKGROUND OF THE INVENTION 
     There are many technologies that have been used for displaying information. One type, liquid crystal, was limited initially to seven segments for displaying numerals, with relatively large segments. As the technology improved, not only could more information be crammed into the same area as before, color became available as well. To avoid plainness, icons were designed to convey information in the name of simplicity, universality, and cuteness. The result is that a modern display can be a forest of data, some symbolic, some literal, to which the user must acclimate, largely by ignoring some of it. 
     It has been found that some data is more intelligible when represented graphically, e.g. an analog clock or a bar graph, rather than digitally as a plurality of numbers. The amount information contained in such graphic displays is relatively small, referred to herein as “low content” information, but is easily and rapidly understood. 
     In some displays, change is used to attract attention. The change can be the apparent motion of a graphic or blinking a graphic on and off. For some liquid crystal displays, the off state may not be truly black, particularly those displays with reflection of ambient light for back lighting. Turning on a mask when the underlying graphic is off can improve apparent contrast. 
     In the last twenty years, a particular class of materials, known as polymer dispersed liquid crystals, has been developed for displays; e.g., see U.S. Pat. No. 4,992,201 (Pearlman). Devices using these materials operate at 60-120 volts peak-to-peak, unlike earlier liquid crystal materials that operated at much lower voltages, and provide contrast without the need for polarizers. Sometimes referred to as “optical shutters,” polymer dispersed liquid crystals have applications outside the realm of displays. 
     U.S. Pat. No. 6,842,170 (Akins et al.) discloses a liquid crystal display combined with an electroluminescent (EL) backlight and a touchscreen. The liquid crystal display is part of a keypad, containing a mask layer with images of the buttons on a telephone (0-9, * and #) and other control buttons. It is also disclosed that the liquid crystal display and the EL backlight can share a common substrate. 
     International Publication WO 2005/121878 discloses a liquid crystal display and an EL backlight on the same side of a substrate. Other permutations are known in the art, with devices on opposite sides of a substrate; e.g., see U.S. Pat. No. 5,121,234 (Kucera) and U.S. Pat. No. 6,441,551 (Abe et al.). Various interlayers or outer layers for affecting optical performance, e.g. color, reflectance, and dispersion, are also known in the art. 
     EL devices are not the only devices suitable for backlighting liquid crystal displays. Light guides coupled to various light sources are known in the art; e.g. Published application 2006/0254894 (Jung et al.) discloses a light guide edge lit by a light emitting diode and having features in the light guide for scattering light out of the plane of the light guide. A difficulty with the light guide is the inability to change output once the backlight is constructed. For example, a light guide can provide reasonably uniform lighting over an area or use features to illuminate selective areas. In either case, the result is fixed and change is costly. 
     The choice of a technology for a particular display is a balance of competing interests, not the least of which is cost. In the case of cellular telephones, the choice is often based on the presumption that the user will be indoors or at least not in direct sunlight when the telephone is used. In other words, the content of the display all but vanishes in bright light because the display relies on luminous backlighting for visibility. Many liquid crystal displays rely on reflective backlighting. Thus, the backlighting increases or decreases with ambient light and the content of the display remains visible. Some displays try for the best of both worlds with a “transflective” layer between a backlight and a liquid crystal module. 
     Although the content of a display may vary, some of the information can be of immediate and continuing interest to a user, e.g. battery life. Thus, it is desirable for some information to be continuously visible, regardless of ambient light level. It is also desirable for a display to make important information conspicuous. Further, it is desirable to have a display that is readily changeable at low cost. 
     In view of the foregoing, it is therefore an object of the invention to simplify the content of a display by obscuring some information during at least one mode of operation and showing the information during at least one other mode of operation. 
     Another object of the invention is to provide a display of low content information that can be located optimally in a system and be obscured or legible, as desired. 
     A further object of the invention is to provide a backlight that provides selective lighting even when using a light guide. 
     Another object of the invention is to provide selective control of reflectance from an EL backlight. 
     A further object of the invention is to provide a display that can be easily changed at low cost. 
     Another object of the invention is to provide a light switch having plural shutters that enable a display to simulate animation or motion. 
     SUMMARY OF THE INVENTION 
     The foregoing objects are achieved by the invention in which a display includes a light switch overlying a backlight and having at least two light shutters which do not, by themselves, convey information by the shape thereof. The lit area of the backlight is equal to or greater than the sum of the areas of the shutters within the area. The display can also include a graphics layer overlying the light switch. The information content of the display is changed by changing the graphics layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a cellular telephone having backlit areas constructed in accordance with the invention; 
         FIG. 2  is a front view of a folding cellular telephone having backlit areas constructed in accordance with the invention; 
         FIG. 3  is a front view of an unfolded cellular telephone incorporating backlit areas constructed in accordance with the invention; 
         FIG. 4  is a plan view of an instrument panel incorporating backlit areas constructed in accordance with the invention; 
         FIG. 5  is a perspective view of a portable computer incorporating backlit areas constructed in accordance with the invention; 
         FIG. 6  is a cross-section of a thick film, electroluminescent lamp constructed as known in the art; 
         FIG. 7  is a cross-section of a polymer dispersed liquid crystal display constructed as known in the art; 
         FIG. 8  is a cross-section of a back light in the form of a light guide edge lit by a suitable light source; 
         FIG. 9  is a cross-section of a display including a light switch having plural shutters and constructed in accordance with a preferred embodiment of the invention; 
         FIG. 10  illustrates the operation of the display illustrated in  FIG. 9 ; 
         FIG. 11  is a cross-section of a display including a light switch constructed in accordance with an alternative embodiment of the invention; 
         FIG. 12  is a plan view of the light shutter illustrated in  FIG. 9 ; 
         FIG. 13  is an expanded view of a display constructed in accordance with the invention; 
         FIG. 14  is a timing diagram illustrating the operation of the embodiment of  FIG. 13 ; and 
         FIG. 15  is a plan view showing one state of the display illustrated in  FIG. 13 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a perspective view of a cellular telephone, meant to also represent any personal electronic device that does not open or unfold in some way. Telephone  10  includes display  12  where the information typically associated with telephones is displayed. In addition, and not part of display  12  or keypad  14 , are backlit areas  17  and  18 . These displays can be used for low content information, such as signal strength, battery life, or roaming. The number of backlit areas is a matter of design, depending, in part, on the nature of the particular portable electronic device. 
       FIG. 2  is a front view of a folding cellular telephone incorporating backlit areas constructed in accordance with the invention and represents any portable electronic device having a folding structure. Telephone  20  includes backlit areas  23 ,  24 , and  25  formed on, in or under shell  26 . As with the embodiment of  FIG. 1 , these displays can be used for low content information. 
       FIG. 3  is a front view of an unfolded cellular telephone incorporating backlit areas constructed in accordance with the invention and represents any portable electronic device that unfolds for operation. Telephone  30  includes display  31  and keypad  32 . Telephone  30  also includes backlit areas  34  and  35 . 
       FIG. 4  is a plan view of an instrument panel incorporating backlit areas constructed in accordance with the invention. The instrument panel could be used in any type of vehicle such as automobile, aircraft, motorcycle, or heavy equipment. Instrument panel  40  includes gauges and displays appropriate for the particular application. In accordance with the invention, instrument panel  40  includes backlit areas  43 ,  44 , and  45 . These displays provide low content information, such as heading, operating hours, battery condition, or status of a safety device. 
       FIG. 5  is a perspective view of a portable computer incorporating backlit areas constructed in accordance with the invention. Computer  50  includes backlit areas  53  and  54 . These displays provide low content information, such as detecting a wireless network or battery condition. One or more backlit areas could be located on the outside of computer  50 , as in the embodiment of  FIG. 2 . 
       FIG. 6  is a cross-section of a thick film, electroluminescent lamp constructed as known in the art. None of the drawings is drawn to scale, within a drawing or from figure to figure. Some layers, such as indium tin oxide, are quite thin, on the order of angstroms. Other layers are quite thick, such as substrate  61 , on the order of mils (0.025 mm). 
     In  FIG. 6 , transparent front electrode  62  overlies transparent substrate  61  and is a thin layer of indium tin oxide (ITO) or indium oxide. Phosphor layer  63  overlies the front electrode and dielectric layer  64  overlies the phosphor layer. Layers  63  and  64  are combined in some applications. Overlying dielectric layer  64  is opaque rear electrode  65 . An optional backing layer (not shown) may also be provided, e.g. for insulating the rear electrode. Coated phosphor particles are used, eliminating the need for a sealing layer. 
     The phosphor layer, or an additional layer, may contain additives for color correction, to assure that the color of the light reflected when the lamp is off is close to the color of the light emitted by the lamp when turned on. Light is emitted through transparent substrate  61 . Electrode  62  or electrode  65 , or both, can be patterned, dividing the backlight  60  into a plurality of EL lamps, collectively referred to as an EL panel. 
     The phosphor and dielectric layers can be interchanged, in which case rear electrode  65  must be transparent. For this construction, light is emitted through the rear electrode. 
       FIG. 7  is a cross-section of a polymer dispersed liquid crystal module constructed as known in the art. Module  70  includes substrate  71  having a transparent conductive layer, such as ITO, overlying a major surface. PDLC material overlies electrode  73  and transparent electrode  74  overlies the PDLC material. Layer  75  is an insulating or protective layer. If one or both of the transparent electrodes is suitably patterned, the module displays the information represented by the pattern. 
     In portable electronic devices, an EL lamp is powered by a driver that converts low voltage direct current from a battery into high voltage alternating current. In order for an EL lamp to glow sufficiently, a peak-to-peak voltage in excess of about one hundred volts is necessary. This is the same voltage necessary for operating a PDLC display. This enables one to use the same driver for both devices, simplifying construction and lowering costs. 
       FIG. 8  is a cross-sectional view of a back light constructed as known in the art. Light guide  81  is a transparent sheet, e.g. of polycarbonate. Light source  82 , e.g., one or more light emitting diodes, emits light into the edge of guide  81 , which conducts the light transversely, as illustrated in  FIG. 8 , substantially by internal reflection. Optional cladding layers  84  and  85  are provided to enhance total internal reflection. Features  87  and  88  at one major surface of light guide  81  upset the total internal reflection, causing light to be emitted from the opposite major surface. Several different kinds of light sources are known in the art. 
       FIG. 9  is a cross-section of a display including a light switch having plural shutters and constructed in accordance with a preferred embodiment of the invention. Light switch  90  includes backlight  91 , which can be an EL lamp as illustrated in  FIG. 6  or a light guide as illustrated in  FIG. 8 . If an EL lamp constructed as illustrated in  FIG. 6  is used, the lamp is flipped vertically to cause light to be emitted upwardly through PDLC layer  92 . 
     Light switch  92  includes a plurality of active areas or shutters, such as shutter  93  and shutter  94 . These are areas between electrodes. One electrode can substantially completely cover backlight  91 . The opposed electrode is patterned, e.g. as illustrated in  FIG. 12 , thereby defining the active areas. 
     Overlying layer  92  is graphic layer  95 . This layer includes a plurality of graphics that are to be selectively illuminated. Layer  92  does not contain information. Layer  92  significantly reduces light from backlight  91  in the off or opaque state, whether backlight  91  is luminous or reflective. As illustrated in  FIG. 10 , shutter  93  is on or transmissive while shutter  94  is off or opaque. 
     Although graphics are illustrated as extending through the thickness of the graphics layer, this is for clarity only. The graphics can be on either major surface of layer  92  or contained within the thickness of the layer, depending upon the nature of the graphics. 
       FIG. 11  is a cross-section of a display including a light switch having plural shutters and constructed in accordance with an alternative embodiment of the invention. Compared with the embodiment of  FIG. 9 , the order of the layers is changed, with graphic layer  112  between backlight  111  and PDLC layer  115 . The operation of light switch  110  is the same as the operation of light switch  90 . One could use graphic layer  112  as a substrate for the other two layers. 
       FIG. 12  is a plan view of a light switch having a plurality of shutters in accordance with the invention. Each of electrodes  121 ,  122 ,  123 ,  224 ,  125 , and  126  is coupled to connector area  131  by its own bus bar and defines an active area of a shutter. Lit areas  134  and  135  are also coupled to connector area  131  by bus bars (not shown). 
     The electrodes are transparent and located on transparent sheet  129 . Electrodes  121  and  122  are within lit area  134 . Electrodes  123 ,  224 ,  125 , and  126  are within lit area  135 . The sum of the areas of electrodes  121  and  122  is equal to or less than the area of lit area  134 . The sum of the areas of electrodes  123 ,  224 ,  125 , and  126  is equal to or less than the area of lit area  135 . 
     Each shutter can be, but need not be, operated independently of the other. Each lit area can be, but need not be, operated independently of the other. As also illustrated in  FIG. 12 , each bus bar preferably extends along a long edge of an electrode to reduce voltage drop. 
       FIG. 13  illustrates an example of a display that is constructed in accordance with the invention and simulates motion. Display  140  includes backlight  141 , e.g., an EL lamp, a plurality of shutters  142 , and graphics layer  143 . The graphics layer includes text areas  151  and  153  and symbols  154 ,  155 ,  156 , and  157 . The graphics can be positive or negative or a mixture of positive and negative. Shutter layer  142  includes shutters labeled A through H. The shutters are operable independently of each other. 
       FIG. 14  is a chart illustrating the operation of the shutters. Shutters D and E are omitted from the chart because they are “on” or “open” anytime the backlight is “on.” Shutters D and E permit backlight  141  to shine through text areas  151  and  152 . In  FIG. 14 , a shutter is “on” or “open” when the line representing the shutter is raised, as indicated by arrow  161 . As illustrated in  FIG. 14 , shutter A opens first, then shutters B and F, then shutters C and G, then shutter H. 
     As illustrated in  FIG. 14  there is no overlap between the sequences of shutter openings. For example, shutter A closes as shutter B opens. There could be overlap, depending upon the optical effect one is trying to create. There is a gap or delay, Δ, between shutter H closing and the cycle beginning with shutter A opening. The delay can be zero or as many seconds as one wishes, again depending upon the optical effect one is trying to create. 
       FIG. 15  illustrates the state of display  140  at the time indicated by line  162  in  FIG. 14 . The dashed lines are not part of the display but are included for reference. 
     The invention thus simplifies the content of a display by obscuring or revealing information at predetermined times. Display of low content information can be located optimally in a system and be obscured or legible, as desired. The invention provides selective lighting even when using a light guide and provides selective control of reflectance from an EL backlight. By not patterning the EL backlight, one can reduce costs even more. Graphics are easily and quickly changed by simply changing the graphics layer. 
     Having thus described the invention, it will be apparent to those of skill in the art that various modifications can be made within the scope of the invention. For example, additional layers, color filters, coatings, screen printings, additional graphics, and the like can be added to any layer, or between the layers, to affect the optical properties of the light switch. In some applications, the graphics layer can be omitted; in which case, one or more shutters can provide a decorative effect. Although PDLC is preferred for the light switch, electrochromic materials can be used instead. Similarly, sputtered ITO is preferred as the transparent conductor but other materials can be used instead; such as, PEDOT:PSS, nanoparticle ITO, or acicular ITO. The substrate material is preferably PET but polycarbonate or urethane can be used instead, among other materials.