Tv: LCD and LED backlight issues

Written by mary carpenter
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Tv: LCD and LED backlight issues
Even the most expensive television can have issues. (tropical landscape on flat screen tv image by javarman from Fotolia.com)

LED backlit LCD televisions have been on the shelves of established stores since 2007, when Samsung released its LN-T4681F model. Reviews of LCD TVs since then have said they don't create black colours as deeply as plasma televisions. LED TVs are basically LCD (liquid crystal display) TVs that are backlit with light-emitting diodes in place of the standard CCFL (cold-cathode fluorescent lights) back lighting, and several issues concerning picture quality have been raised by reviewers.

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Edge-Lit

While performance in general will vary largely between models and manufacturers, the most significant advantage to the edge-lit with LED back lighting design is televisions that can be manufactured much thinner than other designs. However, one of the most notable negative aspects is that the back lighting has a tendency to be not quite as uniform as it should be. For example, the outer edges of a white image on the screen may be noticeably brighter, but the edges of an all-black image may have a distinctly grey hue. With or without local dimming, few major quality benefits have been produced using the LED edge-lit technology. Some LED TVs have been reviewed as having a worse picture quality than the standard CCFL backlit models.

Full-Array Back Lighting

One of the main issues with LCD TVs in general is that the picture will degrade noticeably if the viewer sits to one side, or if the television is set too high or too low. The viewer's eye level will determine how severe the problem is, and LED back lighting doesn't change this. In some cases, the back lighting was believed to make the effect worse. To produce a full-array backlit television that features local dimming, engineers would need to include 2.1 million LEDs that would individually light the 2.1 million pixels in set with 1,080-pixel resolution. Using that many LEDs isn't cost-effective; engineers have stated that as of late 2010 the limit on the number of LEDs they can add to a screen before making the final product outrageously expensive has been reached for the time being.

Local Dimming

The most current and up-to-date local-dimming technology has been found to produce an effect that known as "blooming." This is when brighter areas of the picture bleed into darker areas and lighten the adjacent black levels. This effect will vary widely between models and manufacturers, and edge-lit models have this issue more often than backlit models, but no manufacturer has been able to produce a TV that does not suffer this problem when viewed from odd angles. Blooming occurs in direct relation to how many local-dimming LED elements, known as "dimmable zones," are used behind the screen. Most manufacturers don't release specific information on this.

Tv: LCD and LED backlight issues
Often, the larger the television, the more that imperfections will be obvious. (full hd lcd tv image by mattmatt73 from Fotolia.com)

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