How LCD HDTV backlights (CCFL and LED) are used to illuminate their screens, and local dimming, pixel, and contrast ratio are explained."
Liquid crystal display (LCD) high definition televisions (HDTVs) have typically used miniature cold cathode fluorescent lamps (CCFLs) as backlights or edge lights to illuminate their screens. CCFLs limit color rendition, dim over time and need to be replaced, and contain mercury. Light emitting diodes (LEDs) used as backlights provide a wider range of colors, don't need to be replaced, use less power, and do not contain mercury.
Using "local dimming" technology, an LED backlight can be turned off on dark image areas to make blacks as dark as possible by completely shutting off a pixels light source. Conversely, groups of pixels can be controlled locally to produce more light thereby increasing the brightness of the picture when necessary. In digital imaging, a pixel (picture element) is the smallest item of information in an image represented using dots, squares, or rectangles. The intensity of each pixel is variable with red, green, and blue components.
"LED TVs" are able to achieve striking contrast levels and express "actual black levels" resulting in a 1,000,000:1 dynamic contrast ratio for a sharp, full, HD 1080p picture. Contrast ratio is the ratio of the luminance of the brightest color (white) to that of the darkest color (black) that the system is capable of producing. High contrast ratios are a desired aspect of any display and successful in eliminating the grayish-black picture afflicting many LCD HDTVs.
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