Film-Tech Forum ARCHIVE: LCD projector -- best rest state

This is topic LCD projector -- best rest state in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Frank Angel (Member # 248) on 07-20-2012, 11:08 PM:

We have an LCD projector that needs to be left on for long lengths of time; a mechanical shutter is rigged in front of the lens while there is no mechanical shutter in the projector itself to block light from the lamp from hitting the LCD chip.

We were having this discussion/argument: when the projector is "waiting" for programming and needs to have the lamp on, what is the best way so as not to stress the LCD chip -- feeding the chip full aperture white light or going to black?

Normally most would instinctively go to a black screen, but we were discussing, doing that requires the LCD panel to block, i.e., absorb light and heat energy, always stressing/aging for almost any material. Conversely feeding the projector a white screen would have the LCD chip PASS that light energy rather than needing to block/absorb it.

We have a mechanical shutter in front of the lens, so whether the projector is allowing white light to pass or not is irrelevant. The question simply was, which state is better for the LCD chip?

Discuss amoung yourselves.

Posted by Carsten Kurz (Member # 5396) on 07-21-2012, 06:01 AM:

What projector is it?

Hard to tell, but I would use full white 'passthrough' + external blocking. Mabe there are other means to reduce the aging additionally.

- Carsten

Posted by Frank Angel (Member # 248) on 07-21-2012, 10:04 PM:

I've got two of them -- one is a Sharp NoteVision XG-P10XU 3000 lumen single chip LCD, the other is an Eiki LC-XT3 3 chip 10,000 lumen LCD.

I am with you Carlsten, I think passing the light energy thru the chip(s) has to be less stressful given that the light energy does not have to be "held back" by the crystals. I can't imagine requiring them to block high intensity light for hours in black state can be better than passing that energy.

Posted by Carsten Kurz (Member # 5396) on 07-22-2012, 05:26 PM:

Hmm, neither of them has a dynamic Iris between lamp and optical block - which would reduce light energy a lot during black image. The Eiki has a switchable Eco mode - maybe that feature could be used as well.

I have seen so many Eikis with washed out LCDs...

- Carsten

Posted by Jake Spell (Member # 5294) on 07-29-2012, 03:37 PM:

Logically I would agree that passing the white light though would be the least destructive. That way the mechanical aperture gets most of the heat and not the LCD chips.

Posted by Scott Jentsch (Member # 1681) on 07-31-2012, 10:50 AM:

Whether the LCD is blocking the light or passing it through, the panels are still bearing the brunt of the light hitting it.

Unless the design of LCD panels has changed since I last worked with them, the idle state of an LCD panel is transparent. When current is applied, that portion of the panel becomes opaque (or as opaque as it can).

So that means that the panels are still being heated by the lamp, no matter what. You are then left with whether activating the panels reduces the life of those panels, which I would believe it would.

If it were me, I would allow the light to pass through completely, and shutter it mechanically, but I'll bet the most amount of stress on the panel(s) is going to be from the heat of the light itself, not the activation of the pixels in the panel(s).

Can the projectors go into a power-save mode, where the lamp dims when it doesn't get a signal for a set amount of time? I wouldn't want to turn the lamp off because of the additional lamp strikes it would create, but dimming the brightness of the bulb should be less stressful on all the components in the projector.