I spend most of my days at CES covering the show floor and digesting about 100 major product introductions, but occasionally there's time for a little schooling as well.
That's what happened during my visit to the Samsung booth, where senior marketing manager Dan Schinasi gave me a quick lesson on LED backlighting. In a nutshell, he said, you can't have both a super-slim design and a useful feature called local dimming—at least not yet.
As Dan explained it, some LED backlights use "full-frame" LED lighting across the entire panel. The panel can be divided into small segments—typically 128 to 240—that can be controlled independently. This enables some parts of the screen to go very dark while others stay very bright. Our tests have shown that can improve both contrast and black-level performance. The Samsung A950 series LCD, which has LED backlighting with local dimming, had the best black levels we've so far seen from an LCD set.
Super-slim LCDs, on the other hand, use what's called "edge" LED backlighting. This places LED lights around the perimeter of the panel's frame. Because the LEDs aren't spread across the entire panel, these sets cannot be locally dimmed. So theoretically, at least, there's a tradeoff when you make a set less than two inches thick.
Another difference is that some manufacturers (including Samsung) use white-light LEDs, while others (such as Sony and Sharp) tout RGB-colored LEDs.
The over-lit CES floor isn't exactly the best place to evaluate the effect these differences have on performance, but we'll be investigating that as we test more sets with LED backlighting. In the meantime, watch my video report—done in collaboration with Which?, an independent consumer magazine in the United Kingom— on LED backlight by clicking on the embedded player on the right. (You can also watch a larger-sized version of the video on ConsumerReports.org's Video section.) Stay tuned.
—James K. Willcox
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