Edge-lit vs. Lo­cal Dim­ming

NOVO - - TV BUYER GUIDE - Jeremy Phan

Buy­ing a new tele­vi­sion, de­spite the myr­iad of spec­i­fi­ca­tions, tech­nolo­gies, res­o­lu­tions, and other fac­tors, doesn’t have to be a be­wil­der­ing quest. With the shut­ter­ing of plasma tech­nol­ogy by Pi­o­neer, Sam­sung, and oth­ers, the only re­main­ing main­stream tech­nol­ogy is LCD, which con­tin­u­ally gets bet­ter and bet­ter. Vir­tu­ally all mid-to­high-range LCD dis­plays now use LED back­lights (in­stead of CCFL), with ei­ther lo­cal or edge-lit dim­ming to en­able deeper blacks and richer, brighter colours. 3D didn’t take off as man­u­fac­tur­ers and stu­dios wanted but has nonethe­less, helped to im­prove per­for­mance by in­creas­ing re­fresh rates, colour gamut, and other spec­i­fi­ca­tions that are also used for 2D video. Start­ing off with res­o­lu­tion and end­ing with bud­get, the list of ques­tions a con­sumer needs to ask is now much more suc­cinct. At their core, all LCD dis­plays con­sist of a white back­light sit­ting be­hind an RGB (red, green, blue) LCD panel. The back­light shines light for­ward, while the LCD con­trols the pas­sage of the back­light to il­lu­mi­nate each in­di­vid­ual colour pixel. In older LCD dis­plays, the back­light was of­ten a sin­gle unit which could not vary its light out­put across the screen and more im­por­tantly, not turn off. This in turn, made it very dif­fi­cult for older LCDs to de­liver truly dark blacks, of­ten dis­play­ing them as dark grey or blue. One ad­van­tage of the now de­funct plasma tech­nol­ogy, by virtue of its process, was its abil­ity to not il­lu­mi­nate in­di­vid­ual pix­els as needed. Ad­vance­ments in LCD back­light tech­nol­ogy, beyond mov­ing to higher qual­ity LED back­lights, now in­clude edge-lit and lo­cal dim­ming, split­ting the back­light into mul­ti­ple zones for more re­fined con­trol.

The back­light, there­fore, is now the one of the spec­i­fi­ca­tions that has the largest ef­fect on pic­ture qual­ity. Edge-lit dis­plays are the cheaper of the two ver­sions and use back­lights ar­ranged around the edge of the dis­play. Un­for­tu­nately, there are nu­mer­ous edge-lit back­light con­fig­u­ra­tions used by each man­u­fac­turer, with vary­ing pic­ture qual­ity, de­pend­ing on the price of the TV. If the edge-lit back­light is only along one edge, it ef­fec­tively cre­ates rows or col­umns of back­lights. If more back­lights are used, such as top/bot­tom, right/left, or all four sides, this in­creases the ef­fec­tive ad­dress­able back­lights ar­eas. The more pre­cise the edge-lit back­light con­trol, the darker the im­age can get, and the higher the re­sult­ing con­trast and sub­se­quent pic­ture qual­ity.

Back­lights can fur­ther be re-

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