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.