The recent announcement of LED backlit BRAVIAs (for the UK) and talk of using lasers/LEDs instead of bulbs in projection displays has me wondering about the effect that the spectrum of a display's light source has, as many articles point out how much ‘purer’ these light sources are, saying that it will improve the image quality. (the spectrum is just narrow red/green/blue peaks)

I realise that there are some obvious differences with these technologies — longer lifetimes, differences in power consumption, they allow for much wider gamuts, LED backlighting offers local dimming to increase contrast and so on.

However, wide colour gamut CCFL backlit LCDs already exceed the Rec.709 colour space, so extending the gamut has no obvious benefit. (there is xvYCC, but that's basically irrelevant right now)

Obviously LED local dimming will have an effect on the image, but while it may improve contrast, I'm not convinced that it is of any benefit if you are wanting an accurate image. (similar to how you would disable dynamic contrast on a regular LCD)


Say you were to compare a WCG-CCFL backlit LCD with an LED backlight LCD. For the sake of this comparison, lets say that local dimming has been disabled so the contrast ratio is the same. Both displays are hooked up to a Radiance and are fully calibrated. So greyscale, gamma, white-point, black point etc. is the same. Both displays already exceed the Rec.709 gamut, so the Radiance's CMS is used to get them both as accurate as possible.


So on paper, these displays should look the same, but this ‘purer’ backlight is supposed to improve image quality. Will there actually be any effect, or will both displays look the same?


Perhaps this is a stupid question, but I was just curious, as the new LED backlit displays are roughly twice the price of the WCG-CCFL backlit ones, and local-dimming aside I'm not sure if there are any improvements there to warrant the additional cost.

Andrew, if you were comparing properly calibrated displays, I'm pretty sure the light source wouldn't matter. After all, in calibrating, one should be accounting for the entire display chain: source, display (including the internal light source), and screen. In an UN-calibrated display, it might make a visible difference. Any talk about "purer" light sources in context of a calibrated display is just marketing twaddle. OTOH, if this source's spectrum is closer to the standard CIE observer curve than current backlights or bulbs, it may let both pro and DIY calibrators use less expensive tristimulus colorimeters instead of photospectrometers for calibrating these displays. I'd hazard a guess that it also might help the out-of-the-box primaries be a little closer to the standards, with or without a CMS

I think one of the benefits of a light source with a more "correct" spectrum, is that less tweaking is needed to calibrate them, and thus they are able to retain more of their brightness after the calibration.

Rob

The "color" of the light is everything. Let's remember even in a calibrated TV you are minimizing errors. For example, in a SXRD, the light has a blue bias to it. The closer you can get to a proper spectral balance the easier it is (in theory) to bring everything in line. Witness the Qualia 006 which was touted to have a very accurate light source for the $30k price tag.

I am not sure that has anything to do with retaining brightness and less color change after calibration. That will depend on what the source itself and something we will only be able to judge over time. Let's not forget all the issues we have seen with the newest technology that was unexpected - the SXRD OB issue and issues with the Mitsubishi LaserVue even before it has come to market. Time will be the final judge.

The "color" of the light is everything. Let's remember even in a calibrated TV you are minimizing errors. For example, in a SXRD, the light has a blue bias to it. The closer you can get to a proper spectral balance the easier it is (in theory) to bring everything in line. Witness the Qualia 006 which was touted to have a very accurate light source for the $30k price tag.

I am not sure that has anything to do with retaining brightness and less color change after calibration. That will depend on what the source itself and something we will only be able to judge over time. Let's not forget all the issues we have seen with the newest technology that was unexpected - the SXRD OB issue and issues with the Mitsubishi LaserVue even before it has come to market. Time will be the final judge.

I agree that a more accurate light source should mean less effort for a calibrator to dial in the grayscale and color on a particular display. Here's hoping there aren't other issues with these that negate the advantages of the new light source!;)