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Do you see DLP rainbows and CRT monitor flickers?

1224 Views 14 Replies 12 Participants Last post by  Dean McManis
I have a theory I'd like to test. I think that people that see DLP rainbows are also sensitive to CRT monitor flickering (at 60 Hz vertical refresh). That is, if you need a high CRT monitor vertical refresh rate (>=75Hz), then you are likely sensitive to DLP rainbows.

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Hmmmm. I wish the poll question had been phrased a little differently. Yes, I do see CRT flicker on monitors and such set below 75Hz. Now, I only use LCD monitors for computing. So, count one vote moved into the "I see both" from the "I see rainbows but not CRT".

I see DLP rainbows on 2.5x color wheels. On the 5x wheel on the Sharp 9000, I only saw subtle rainbows on very high contrast scenes with bright pinpoint sources on dark backgrounds (street lights and such). They're also most noticeable on black and white material (obviously -- any color is obvious on B&W). On the LT150, I noticed them much more often.
The rainbow:non-rainbow ratio is running about 3:1.

Excellent poll!

One additional choice might have been "I see DLP rainbows, but I don't let them get me down."
I don't think we've reached a statistically significant sample size yet but the myth of DLP rainbow sensitivity being a "minority" issue is seriously threatened here.

Every single speed color wheel DLP projector I've seen sends me into rainbow agony. It's nice to know I'm not alone.

...and pixel structure.

...and I can hear the squeal of a standard NTSC set, if overdriven, from 30 feet away.

...and the chroma bug

...and absolute polarity in sound

How do we ever enjoy these things?!

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Last night I saw a old Seleco 200 DLP. I saw NO rainbow. I only see a hair amount of subtle rainbow on the LT150 around bright object edge moving on a dark background. I saw NO rainbow in the new Seleco 200DM and the Sharp Z9000.

I see 60hz flicker on PC monitor but not on a CRT projector.


Li On
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I think there's enough samples to post some preliminary results. Of course, this is not a scientific poll, but I still think the results are interesting.

Lets define the following state variables:

CRT = you see flicker in a 60 Hz CRT monitor

DLP = you see rainbows in a DLP projector

At this time,

P(DLP & CRT) = 18/40

P(DLP & !CRT) = 12/40

P(!DLP & CRT) = 4/40

P(!DLP & !CRT) = 6/40

I was interested is seeing how correlated CRT and DLP are. The below are conditional probabilities:

P(DLP | CRT) = P(DLP & CRT) / P(CRT) = 9/11

P(CRT | DLP) = P(CRT & DLP) / P(DLP) = 3/5

What this means is if you see CRT flickering, you have a 9/11 chance of seeing DLP rainbows. And if you see DLP rainbows, you have a 3/5 chance of seeing CRT flickering.

So how can you use this info? Suppose you are looking at purchasing a projector via mail order, but you can't view a DLP one because you live in the middle of nowhere. If you know you are sensitive to CRT flickering, then you have a 9/11 chance of seeing rainbows on a DLP projector. However, if you know that you aren't sensitive to CRT flickering, then you have a P(DLP | !CRT) = 2/3 chance of seeing rainbows on a DLP projector. While still not very good odds, do improve your odds of predicting if you'll see rainbow given your CRT sensitivity.

Note that P(DLP) = 3/4. Maybe someone from TI can tell us if this number jives with their stats.

I have a LP150 DLP projector, and see rainbows and CRT flicker. At first I was a bit bothered by them, but now I rarely see them. I think I must be getting use to them, and I am very happy with my LP150.

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Great work, Ross! That is an interesting correlation.

If nothing else, this poll might just allow those who do see these effects to (finally) accept that some folks really can't see them.

Of course, it should also serve to point out to those who really can't see these effects that there are people out there who not only see them, but are really bothered by them.

In a nutshell, maybe it isn't fair to say "Model xxx doesn't have rainbows", since it certainly does seem to vary from person to person.
I see rainbows in DLP and some rear projection CRTs and CRT's flickering. Maybe over time your eyes become conditioned to quit roaming over the screen and focus more on the picture for fear of seeing rainbows.

Kei Clark
I see...dead people.
Originally posted by JustMike
Hmmmm. I wish the poll question had been phrased a little differently.
Same here. I voted before reading the post. I see both when the CRT is refreshed at 60Hz. Bump that up to 72Hz and the CRT flicker is gone.

Would be interesting to find out which of these categories are susceptible to dlp headache as well...
Whenever I go to the UK or India, I notice 2 things immediately - the better vertical resolution of PAL and the 50 Hz flicker on the TV. That said, I don't seem to notice 60 Hz flicker in North America on TV, but computer monitors refreshing less than 75 Hz can be bothersome.

With the LT150, something very interesting has happened. Just after I got the projector, I used to notice the odd rainbow here and there when watching movies, but it never got in the way of my big screen experience. Now that I have put some 70+ hours on the projector, I find that my 'rainbow perception frequency' has dropped off markedly. Either this is conditioning (I am still seeing them, but my brain is not registering them) or I have trained my eyes into not flitting around too much. In any case, rainbows on the LT150 are pretty much history for me now. Associated hardware is a Panasonic RP-56 and DaLite High Power screen.

p.s. I should add - NO headaches/eyestrain etc at all. Friends haven't complained either.
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I can also see flickering of monitors at 60Hz, but not 75Hz.

I have noticed rainbows on my LT150, but only on one movie, so it's not an issue for me.

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