Warning about ceiling mounting Dalite High Power - AVS Forum
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post #1 of 12 Old 09-26-2001, 03:42 AM - Thread Starter
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I have a LT150 that I ceiling mounted in my HT. I was projecting onto a white wall, which looked great at night, but was washed out during the day (I don't have much lighting control in my HT). I've heard lots of good things about the Dalite Model B High Power for the LT150. My configuration is such that the projector to center of screen to eye angle is 19 degrees. I called Dalite to make sure this configuration would work, as I've also read that the High Power was not necessary good for ceiling mounts. I was told that the viewing angle was 25 degrees, and I was well within that range.

After receiving the High Power, I got NO improvement in brightness compared to my white wall, when viewed either at night or in daylight. Moreover, a blank sheet of white copy paper appeared brighter than the white wall AND the the High Power. I called Dilite to find out why. I was told that I should be getting over 1.6 gain at that angle, but they could not explain why my white wall was equally bright, and the paper was significantly brighter.

In addition, my HighPower was defective, in that the left side of the screen was about 2" longer than the right side. This created (or made worse) some wrinkles that caused very disconcerting motion distortions during panning motions.

I purchased the screen through Cousins Video, who was more than willing to replace the defective screen with a new one. However, since I got no brightness improvement, and I've since read the Model B's are prone to wrinkles, I decided to return it. This was a somewhat costly mistake (20% return charge, $52 shipping UPS ground, plus installation time and hardware).

The moral of the story: The High Power does not seem like a good screen for ceiling mounts, unless your viewing angle is <10 degrees. I also don't believe the verbal specifications I got from Dalite are correct, which they could not provide to me in a printed/online format before or after purchase.

I'm now back with my very flat, white wall, which looks great with my LT150 from any angle.

Ross.
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post #2 of 12 Old 09-26-2001, 10:06 AM
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Ross,

Which white paint are you using on your wall and is it flat, satin, semi-gloss, etc.

Thanks for posting your experience with the Dalite HiPower as I was considering it as a replacement for my $10 white glossy Tileboard from Home Depot. I would be using the hipower with the LT150 near the floor though.

Also, are you sure you that Cousins didn't send you the matte white version?


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post #3 of 12 Old 09-26-2001, 04:26 PM - Thread Starter
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Iceman,
I knew that the High Power is retro-reflective before purchasing it, and Dilite assured me it would work for my installation. It would work fine for ceiling mounts, if your viewing angle is <10 degrees. For me, that would require an movable projector mount.

hardwired,
I have a flat painted wall. It is actually a bit off-white (yellowish), though my brain seems to do dynamic whitebalancing and whites look white to me.

I'm pretty certain this was a High Power, since if I stood up, the brightness of the screen increased significantly (by at least 50-75%). This is characteristic of the retro-reflective screens like the High Power. If you're in this sweet spot, the screen is very nice (except for the wrinkles).

For my installation, a matte white version would have worked just as well. However, the wall works even better, since it is very flat.

Ross.
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post #4 of 12 Old 09-26-2001, 09:01 PM
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Ross,

The High Power is a retro-reflective screen and should therefore only be used for floor mounted projectors. Retro-reflection means that light is reflected back to the source. This does not explain why your gain is below unity at 19 degrees, though.

[This message has been edited by Iceman (edited 09-26-2001).]
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post #5 of 12 Old 09-26-2001, 10:08 PM
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Ross,

I am afraid you got some bad advice from the person at Da-Lite. I'm sure that if Blake Brubaker (I hope I spelled his name right!) from Da-Lite comes by he will echo my comments. A retro-reflective screen is possibly the worst choice for a ceiling mount configuration. Even at a viewing angle of less than 10 degrees you are outside of the sweet spot of the screen, as you discovered when you stood up. You are also quite right that your screen was a high power. A grey screen of some kind would be much better for your application unless you need the extra brightness. Da-Lite is usually pretty good about supporting the users of this forum, they will hopefully work something out with you, either for a higher gain non-retro-reflective screen or an HC Da-mat; especially since you bought it on their recommendation!

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post #6 of 12 Old 09-27-2001, 11:57 AM
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Yes, the High Power may well have a VERY narrow gain cone.

Still, the Da-Lite website states that the "viewing angle" (whatever that means) is 25 degrees. Judging from the data for the various screens, it is hardly the half-gain angle - at least not in every case. I have not been able to find any gain curves, perhaps someone knows how Da-Lite defines viewing angle? Even better, perhaps someone knows where to find the gain curves?
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post #7 of 12 Old 09-27-2001, 01:32 PM - Thread Starter
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The Dalite customer support representative I talked with stated that the 25 degree viewing angle was the angle at which the image appears half as bright compared to viewing at 0 degrees. I inquired about getting a gain curve, but was told none were available (the the CSR apparently had one, since she was reading off values at various angles). From my observations, the High Gain has a half brightness viewing angle closer to 13 degrees, and the gain goes down to unity at 20 degrees. This may be why they don't publish these specifications.

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post #8 of 12 Old 09-27-2001, 10:41 PM
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The viewing angle is not really the problem in this case. It is instead the direction of the 0 degree reference you mention in your post. In a retro-reflective screen the 0 degree reference is pointing roughly back towards the projector where a regular screen has it roughly pointed towards the audience. Obviously, you are then in the bad part of the gain curve.

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post #9 of 12 Old 09-27-2001, 10:50 PM - Thread Starter
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Hi Kam,
By viewing angle, I mean the angle defined by the projector to center of screen to my eye (see my original post). This is also what Dalite says their specifications is based on. According to Dalite I should be well within the gain curve (at least 1.6), but it is clear that I wasn't.

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post #10 of 12 Old 09-28-2001, 01:50 AM
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Ross,

The presented viewing angles are hardly half-gain angles in every case - just take a look at the values for the lower gain screens. I always get very uncomfortable with companies that cannot get their specs straight.

Kam,

Actually, with a ceiling mounted projector and a viewing position vertically centered relative to the screen, it does not matter whether you have Snell's law reflection (i=r) or a reflection back to the source. The off-axis angle remains the same, although most of the light either goes towards the floor or the ceiling.

Apart from this, the angle Ross is defining should, in combination with the gain curve, give us an answer that roughly correlates with subjective findings. My guess would be that the gain cone is much more narrow than the specs would indicate, just as Ross observed. Perhaps the stated 25 degrees relates to the cone opening angle i.e. twice the angle Ross defines. This would be a ridiculously narrow cone, though.

[This message has been edited by Iceman (edited 09-28-2001).]
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post #11 of 12 Old 09-28-2001, 10:40 PM
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Iceman,

In the case of the 150 I might agree with you, because it has a large offset angle. Of course, both our posts are really gross over-simplifications, there are portions of the screen in both cases that are in the optimum part of the gain curve and large areas that, obviously, are not.

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post #12 of 12 Old 09-29-2001, 03:08 AM
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Yes, we are simplifying quite a bit. You really need a good simulation to fully understand what compromises you are willing to accept.

From my ray-tracing screen computer simulations, the only >=2 gain screen material I would even contemplate using for a flat screen is the Stewart UM200. There may be others but the gain curves for all other materials I have seen just don't cut it. Any info regarding gain curves would be much appreciated.

Currently I am using movie frames for evaluation. In combination with the calculated screen/viewing position/pj position dependent illumination, the frames provide very valuable insights as to what screens are acceptable - much more so than a full white field.
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