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A light-emitting diode (LED) backlight combines a liquid crystal display (LCD) with an LED light source to generate color on computer and TV screens. LED backlighting is needed to produce light and color from behind the screen of a device. This technology is able to produce a wide array of colors and comes as either an edge-lit or local-dimming LED backlighting system. The use of LEDs makes it easier for consumers and workers to look at a screen without eyestrain, though eyestrain will still occur if the screen is looked at continuously for several hours. Uniformity of color is easy to maintain when LEDs are new, but LEDs tend to age at different rates, so color may change in one section of the screen.
In most screens, backlighting is needed to produce light and color. This simply means there is a light behind the screen, and it is being pushed through the LCD. LCDs cannot produce light, and whatever is producing the light changes the properties of the screen.
In LED backlighting, an array of small diodes are used that are either white — really blue with yellow phosphor to create white, because there is no white LED — or Red Green Blue (RGB) LEDs. White is used in cheaper screens, while RGB can produce a higher variety of color. LED backlights are used mostly for smaller screens such as TVs and computers, because LEDs cannot produce the necessary amount of brightness for larger displays.
LED backlighting comes in two varieties: edge-lit and local dimming. Edge-lit runs LED strips along the edges of the screen, meaning the light’s glow is directed toward the center of the screen. This is cheaper, but causes black to appear gray. Local dimming uses a grid of LEDs across the entire screen, which means better color control — and black actually appears black.
In older screens, especially computers, an incandescent light bulb and filament were used to generate light. This approach lit up the entire screen indiscriminately and made closed sections of the LCD light up anyway, so it caused massive eyestrain for computer users and anyone else looking at a screen. LED backlighting only lights a portion of the screen, making it easier to look at a screen for a prolonged amount of time. This can still cause eyestrain, but the chances are reduced.
The problem with LED backlighting is that a large number of different diodes are used at once. Each diode ages at a different rate because of color usage or differing factors during manufacture, so some lights will age quickly, while others will age slowly. This means a section of the screen may appear dimmer because the LEDs there are worn, causing color uniformity to be unstable.