# LCD tv DLP or other LED instead of xenon?



## Northernflame (Apr 15, 2007)

Hello.

I was recently going over the rear projection TV lamp costs. Yeah well 200$ is quite a bit for something with such a short lifespan.

I'm curious as to why there are no luxeon led projection lamps. Even 3 watts but 5watts would be better luxeons or even cree's should in theory work.

There are digital LED projectors that project fine detail metres away.

Should be no problem for a screen that is mier inches away.

Besides LED have a much better natural light spectrum over xenon.

Any comments?


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## 2xTrinity (Apr 15, 2007)

> There are digital LED projectors that project fine detail metres away.
> 
> Should be no problem for a screen that is mier inches away.
> 
> Besides LED have a much better natural light spectrum over xenon.


There's no way that even the brightest single-emitter LEDs on the market will come close to the amount of light required for most DLP TVs. A typical projector is only something like 10-20% efficient when comparing total lumens from the lamp, to lumens out the front--that's why the light sources are usually metal-halide, or xenon-arc lamps running hundreds of watts, with dedicated fan cooling. And those lamps are already about as efficient as the best LEDs.

Now, using three separate LCD chips, and separate high-powered red, green, and blue emitters ought to do the trick, but IMO a projector would have to be engineered to use that from the beginning for it to work well.


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## Sable (Apr 15, 2007)

The lamp in my DLP seems to be at least partially mercury-filled - lots of "Lamp Contains Mercury" stickers.

The amount of light my TV (A Toshiba 62HM195) requires is fairly insane. The lamp is driven at about 150 watts, and I've never seen any indication of a lack of colour range, so I'm going to say that it's probably got a very high CRI. The image is beautiful and crisp, and so bright that I leave the lamp on the "low" setting even in bright daylight. I believe that in this power range, gas discharge lamps produce _hundreds_ of lumens per watt.

Samsung does produce an LED-backlit DLP TV. It's 56" wide and quite impressive, and about twice the cost outlay of its competitors. I've not had the opportunity to see one extensively myself, but there are advantages: Beyond simply having no bulb to replace it also did away with the colour wheel, another weak spot of DLP televisions and projectors. This means one less part to ever break [Though colour wheel failures are unlikely], as well as the elimination of the "Rainbow Effect," which I can see but it doesn't bother me. I have no idea what LEDs Samsung is using.

I'm a big fan of DLP. My bulb is rated for 6000-8000 hours use on the "low" setting, and my usage patterns are that this should last me two to four _years_ - I play video games and watch movies. I don't have cable for a variety of reasons, not the least of which is I can't stand most cable programming. Considering the experience that I get, I feel that the cost of bulbs - I have two spares - is very reasonable. They can be a little hard to find, but armed with a part number and Google, one can usually find reputable and good deals.


"White" LEDs also _don't _have stellar spectrum ranges. They're very heavy in blue, don't have a lot of red. I would much prefer high-power discrete red, green, and blue LEDs in this kind of application, but considering the power levels involved you would have to design from the ground up to be using quite possibly _multiple_ polycore LEDs - something like the Osram OSTAR 10/15 watt devices. Luminaires and other optical systems designed for arclamps and other point light sources can't work here, since these LEDs have very large (comparative) surfaces from which to emit light, causing a redesign of the entire system - I would bet this is how Samsung did it with their LED DLP.

There are technologies on the horizon for solid-state lighting - "Laser DLP" and SED displays may be coming in the next couple of years, and promise to be very exciting indeed. OSRAM's new thousand-lumen multicore LED device should open the world up to better small projectors and automotive headlights. But for the sheer insane amount of light a good, high quality, HDTV front or rear projector needs, I think discharge lamps are going to be the way to go for a while.


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## 2xTrinity (Apr 16, 2007)

> Beyond simply having no bulb to replace it also did away with the colour wheel, another weak spot of DLP televisions and projectors. This means one less part to ever break [Though colour wheel failures are unlikely], as well as the elimination of the "Rainbow Effect," which I can see but it doesn't bother me. I have no idea what LEDs Samsung is using.


I know that some DLP TVs have done away with the color wheel by using a prism to split the spectrum from an HID lamp up into R/G/B components, followed by using three separate black and white LCDs, and another prism to merge everything back together. Honestly, until LEDs get to the point where they aremore efficient and higher powered so that one emitter in each color is enough to get the job done, I don't see much advantage in using them over the HID lamps.


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## Sable (Apr 16, 2007)

I'm not sure that isn't just "LCD Rear Projection," myself.

DLP units have one chip with a gazillion mirrors on it, and as each part of the colour wheel passes, turns on the red, green, and blue parts of the scene, all unbelievably fast.

Rear projection LCD does exactly what you say - there's no DLP chip and colour wheel, instead either the lamp shines through a very small full-colour LCD panel which is then focused on the screen, or is split by a prism and then through three separate LCD panels as you described.

In other words: "DLP" televisions use the Texas Instruments "DLP" micromirror chip - there are ways to construct them that use either very high speed colour wheels (No rainbow effect) or by eliminating the colour wheel by changing the light source (LEDs), but if it doesn't have the DLP chip, it isn't a DLP device.

ETA: I also think there are some three-chip DLP front projectors, that also use a prism to shoot the red, green, and blue portions of a scene to three different DLP micromirror chips, which also eliminates the rainbow effect. These are, however, enormously expensive as a general rule. Awesome little units, though.


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## 2xTrinity (Apr 16, 2007)

Sable said:


> I'm not sure that isn't just "LCD Rear Projection," myself.
> 
> DLP units have one chip with a gazillion mirrors on it, and as each part of the colour wheel passes, turns on the red, green, and blue parts of the scene, all unbelievably fast.
> 
> ...


You are right. I know someone who has one of the Sony 1080p 50" TVs that works this way, and I was thinking it was DLP, but it's actually just using 3x reflective LCDs.


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## 65535 (Apr 16, 2007)

The fallback of LED's may be one of its best characteristics, LEDs are almost completely non sacrificial, Incans, they sacrafice a filament for light, HID's have electrodes and gasses, LED's are also really low temp, so they don't do well where the relatively small amount of heat generated can be removed.


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## yuandrew (Apr 17, 2007)

The Samsung DLP TVs with model numbers ending in "89S" have the LED light engines. (Example HL-T5689S= 56" DLP with LED light engine)

http://www.samsung.com/Products/TV/dlptv/index.asp


I wonder if anyone makes Flat Panel LCDs with LED backlights.


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## Northernflame (Apr 20, 2007)

yuandrew said:


> The Samsung DLP TVs with model numbers ending in "89S" have the LED light engines. (Example HL-T5689S= 56" DLP with LED light engine)
> 
> http://www.samsung.com/Products/TV/dlptv/index.asp
> 
> ...



Hi.

Thankyou for the sugestions. I went and seen one.

White actualy looks white when compared to my grand wega.

Will update when i buy one.

Tks again.


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