Local Dimming improves black levels and contrast ratios which are comparative weakness of LCD display technology compared to plasma displays.

Local dimming has been associated with full array backlighting where an even array/matrix of LED backlights is placed behind the a diffuser and the liquid crystal display itself. The diffuser is required to ensure that the LED backlighting is spread uniformly across the back of the LCD display panel. Local dimming is the dimming of the LED backlighting in certain areas of the display which are meant to be displaying the darker elements of a scene. This provides a significant increase in contrast ratios and black levels bringing LED LCD HDTVs with local dimming much closer in performance to plasma displays which have, until now, held a distinct advantage.

A problem which can (and has) occurred with local dimming is the manifestation of blooming around bright objects set against a dark background. It is the result of an imperfect match of the brighter backlit area to the displayed bright object area and the leakage of the brighter backlight through liquid crystal shutters surrounding it. Manufacturers have addressed this problem by increasing the number of LEDs and/or reducing the number of LEDs in blocks of controlled backlighting (finer lighting control). Even if blooming does occur it will only be in the relatively small proportion of very dark scenes.

Until recently, LED lights in edge-lit LED LCD HDTV displays could be dimmed in groups to improve black levels but, not individually. The lighting control areas tended to be large reducing the effectiveness. In an effort to deliver the best attributes of both current LED backlighting approaches, HTDV manufacturers have been striving for performance improvements. With the recent release of it’s C8000 and C6800 LED LCD models with Precision Dimming technology, Samsung seems to have won the race. Special edge mounted LEDs enable the controlled lighting of variable size, diamond-shaped areas effectively providing local dimming. Higher contrast ratios, deeper blacks and energy savings are achieved by lighting being varied in intensity to match what is required for the frame being shown.