However, because the spectral curve peaks at yellow, it is a poor match to the transmission peaks of the red and green color filters of the LCD. A white LED is typically a blue LED with broad spectrum yellow phosphor to result in the emission of white light. White LEDs are used most often in notebooks and desktop screens, and make up virtually all mobile LCD screens. Due to the disadvantages in comparison with LED illumination (higher voltage and power needed, thicker panel design, no high-speed switching, faster aging), LED backlighting is becoming more popular.LED backlightsSee also: LED-backlit LCD LCD with LED matrix backlightLED backlighting in color screens comes in two varieties: white LED backlights and RGB LED backlights.
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The heat generated by incandescent bulbs typically requires the bulbs to be mounted away from the display to prevent damage.CCFL backlights 18 parallel CCFLs as backlight for an LCD TV LCD with CCFL backlightFor several years (until about 2010), the preferred backlight for matrix-addressed large LCD panels such as in monitors and TVs was based on a cold-cathode fluorescent lamp (CCFL) by using two CCFLs at opposite edges of the LCD or by an array of CCFLs behind the LCD (see picture of an array with 18 CCFLs for a 40-inch LCD TV). Incandescent backlighting was used by early LCD panels to achieve high brightness, but the limited life and excess heat produced by incandescent bulbs were severe limitations. CCFL backlights are used on larger displays such as computer monitors, and are typically white in color these also require the use of an inverter and diffuser. An ELP must be driven by relatively high voltage AC power, which is provided by an inverter circuit. ELP backlighting is often used for larger displays or when even backlighting is important it can also be either colored or white. White LED backlighting is becoming dominant. Monochrome LCDs typically have yellow, green, blue, or white backlights, while color displays use white backlights that cover most of the color spectrum.UsageColored LED backlighting is most commonly used in small, inexpensive LCD panels. Most use a fixed polarizing filter and a switching one, to block the undesired light.Contents1 Light source types2 Usage2.1 CCFL backlights2.2 LED backlights2.2.1 Backlight dimming3 Diffusers4 Reflective polarizers5 Power consumption6 References7 External linksLight source typesThe light source can be made up of:Light-emitting diodes (LEDs)An electroluminescent panel (ELP)Cold cathode fluorescent lamps (CCFLs)Hot cathode fluorescent lamps (HCFLs)External electrode fluorescent lamps (EEFLs)Formerly, incandescent lightbulbsAn ELP gives off uniform light over its entire surface, but other backlights frequently employ a diffuser to provide even lighting from an uneven source.Backlights come in many colors. Light valves then vary the amount of light reaching the eye, by blocking its passage in some way. The backlight is usually the first layer from the back. Most LCD screens, however, are built with an internal light source.
Wild.Simple types of LCDs such as in pocket calculators are built without an internal light source, requiring external light sources to convey the display image to the user. A review of some early backlighting schemes for LCDs is given in a report Engineering and Technology History by Peter J.
Backlights are used in small displays to increase readability in low light conditions such as in wristwatches, and are used in smart phones, computer displays and LCD televisions to produce light in a manner similar to a CRT display. Backlights illuminate the LCD from the side or back of the display panel, unlike frontlights, which are placed in front of the LCD. As LCDs do not produce light by themselves-unlike, for example, cathode ray tube (CRT) displays-they need illumination (ambient light or a special light source) to produce a visible image. Views of a liquid crystal display, both with electroluminescent backlight switched on (top) and switched off (bottom)A backlight is a form of illumination used in liquid crystal displays (LCDs). For other uses, see Backlight (disambiguation).
For the lighting design practice, see Backlighting (lighting design). For the rear window of an automobile, see Car glass.
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