Backlight
A backlight is a form of illumination used in liquid-crystal displays (LCDs) that provides light from the back or side of a display panel. LCDs do not produce light on their own, so they require illumination—either from ambient light or a dedicated light source—to create a visible image. Backlights are commonly used in smartphones, computer monitors, and LCD televisions. They are also used in small displays, such as wristwatches, to enhance readability in low-light conditions.
Typical light sources for backlights include light-emitting diodes (LEDs) and cold cathode fluorescent lamps (CCFLs).
Simple types of LCDs, such as those used in pocket calculators, are built without an internal light source and rely on external light sources to make the display image visible to the user. However, most LCD screens are designed with an internal light source. These screens consist of multiple layers, with the backlight typically being the first layer from the back.
Light valves regulate the amount of light reaching the eye by blocking its passage in specific ways. Most LCDs use a combination of a fixed polarizing filter and a switching one to block unwanted light.
Many types of displays other than LCD generate their own light and do not require a backlight, for example, OLED displays, cathode-ray tube (CRT), and plasma (PDP) displays.
A similar type of technology is called a frontlight, which illuminates an LCD from the front.
A review of some early backlighting schemes for LCDs is given in a report Engineering and Technology History by Peter J. Wild.
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