LAMP vs. LED

[Shinma]

Originally Posted by welwynnick

Can't wait to see the back of lamps, though I don't think the potential of LEDs has been exploitd yet. The tests I saw said the contrast was lower because of the lack of a dynamic iris, but I don't think that's anything to do with LEDs in themselves. LED sets seem to have potentially the best colour performance of all, though the forthcoming Mitsubishi laser TVs should be good as well.

Nick

As long as the LEDs aren't so dim, and the light so structured, that when they diffuse the array of LEDs to remove the structure the light is transmitted at higher angles than that of a florescent system, I don't see a fundamental reason why the LED TVs should have a worse contrast ratio at the same refresh rate. I would think the LCD portion itself should be the same..... Although, if they are trying to drive them 3 times as fast to cycle the colors, that would have an impact on at least color accuracy, if not contrast.

LEDs have two possible advantages for color performance. The exact color anchoring points are more arbitrary because they aren't constrained by peaks from phosphor, and the band should be more narrow. This last one isn't fundamental, because you could filter the tube output to an even more narrow wavelength range, but you don't want to give up that much light. The laser TVs, on the other hand, have as narrow a band as you can get, but technology limitations may not anchor those colors at the ideal points to cover the largest gamut. With today's technology, high efficiency laser output is pretty constrained to specific wavelengths once you approach wavelengths shorter than mid-red. While they aren't ideal, I think they are far better than the constraints of phosphor, so I anticipate these TVs will look really nice. I'm not sure it's a really fair comparison though, since I think the laser TVs that are coming out are rear projection and not being used as illumination for an LCD screen. Because of price/power and coherence issues, I'm not sure I see them being used as back lighting for an LCD panel.

[welwynnick]

Originally Posted by Shinma

As long as the LEDs aren't so dim, and the light so structured, that when they diffuse the array of LEDs to remove the structure the light is transmitted at higher angles than that of a florescent system, I don't see a fundamental reason why the LED TVs should have a worse contrast ratio at the same refresh rate. I would think the LCD portion itself should be the same..... Although, if they are trying to drive them 3 times as fast to cycle the colors, that would have an impact on at least color accuracy, if not contrast.

LEDs have two possible advantages for color performance. The exact color anchoring points are more arbitrary because they aren't constrained by peaks from phosphor, and the band should be more narrow. This last one isn't fundamental, because you could filter the tube output to an even more narrow wavelength range, but you don't want to give up that much light. The laser TVs, on the other hand, have as narrow a band as you can get, but technology limitations may not anchor those colors at the ideal points to cover the largest gamut. With today's technology, high efficiency laser output is pretty constrained to specific wavelengths once you approach wavelengths shorter than mid-red. While they aren't ideal, I think they are far better than the constraints of phosphor, so I anticipate these TVs will look really nice. I'm not sure it's a really fair comparison though, since I think the laser TVs that are coming out are rear projection and not being used as illumination for an LCD screen. Because of price/power and coherence issues, I'm not sure I see them being used as back lighting for an LCD panel.

I think we're talking at cross purposes. I was referring to DLP rear projection TVs that use LED light sources. So LCD and phosphor technologies don't enter into the equation.

To the best of my knowledge, the first generation or two of LED DLP RPTVs didn't use a dynamic iris to improve the FOFO contrast over and above what could be achieved natively, using just the DMD. Contemporary lamp RPTVs do use DIs, and appear to have greater dynamic contrast. I would very much hope that this situation has improved with LED RPTVs, though I'm disappointed that even after two years, nobody seems to have taken advantage of LEDs ability to source modulate, and achieve unlimited dynamic contrast (see press release below). I presume there are some difficult thermal management issues.

Nick

[welwynnick]

"Las Vegas – June 18, 2008: Texas Instruments (TI) (NYSE: TXN) today at InfoComm DLP® Products introduced the industry’s first home theater lamp-free projector that utilizes a PhlatLight™ LED light source and a BrilliantColor™ chipset. This technology demo delivers a superior 1080p picture for which DLP technology is known, while eliminating maintenance costs such as lamp replacements and filter changes required by some competing projector products. Multiple DLP customers have plans to develop DLP lamp-free LED-based projectors, including Optoma, with units expected to ship in late 2008. Similar to the deployment of DLP Product’s now popular BrilliantColor technology, the solid-state, lamp-free innovation will first be incorporated into home theater units and proliferate through corporate and education product lines thereafter.

Benefits of Lamp-free
Due to the inherent switching speed of the DLP chip and advancements in LEDs from Luminus, a leader in LED manufacturing, consumers will benefit from the increased picture quality, reliability and value found in this new projector category. The reflective nature of the mirrors on the DLP chip allow more light to reach the screen resulting in a 50% increase in color gamut range producing more than 200 trillion colors and a contrast ratio in excess of 500,000:1. The proprietary combination of LED illumination, coupled with DLP technology elevates picture quality to a new level while eliminating the traditional projection lamp.

In addition to the expanded color and contrast performance, the illumination system has an incredibly long life and offers up to 30% lower power usage and, most significantly, hundreds of dollars in savings from lamp purchases."

[Shinma]

Originally Posted by welwynnick

I think we're talking at cross purposes. I was referring to DLP rear projection TVs that use LED light sources. So LCD and phosphor technologies don't enter into the equation.

Nick

Sorry, I didn't realize the conversation/comparison was restricted to arc lamp based projection systems. Still, it doesn't really matter with the point I was making. You just substitute emission area of the arc lamp and spectral peaks for the arc lamp with that of the phosphor for the tubes and it is the same point I was trying to make. As long as the etendue (brightness) limitations for the LEDs aren't an issue to overcome, I would think you could get comparable performance, as you have suggested.