# DLP Rainbow effect demonstrated



## Harpmaker

I took a photo that demonstrates the DLP Rainbow effect. For whatever reason, my DVD player wouldn't play my Digital Video Essentials DVD so I was just using the standard "DVD logo" screen to take the shot.

I held my hand in the PJ beam close the the PJ and wiggled my index finger. The photo shows what I saw with my eyes. There is very little blue in the effect since the color of the portion of the beam I wiggled my finger in was yellow, but you can still see some blue.

The only time I see the Rainbow Effect when watching a DVD is if I move my eyes rapidly from one side of the screen to the other, and it is not very noticeable even then.

The image is large so I'll post a clickable thumbnail.


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## Mike P.

Which brand and model of projector do you have? Not being familiar with DLP's, I'm trying to understand why some DLP projectors have this effect and others don't.


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## Harpmaker

Mike P. said:


> Which brand and model of projector do you have? Not being familiar with DLP's, I'm trying to understand why some DLP projectors have this effect and others don't.


Thanks Mike. I forget to add that info didn't I? :doh:

I have a Viewsonic PJ503D; one of the least expensive PJ's on the market. I've seen them at $299 after rebate! I wish I have gotten mine that cheap...

If I understand things right, all single-chip DLP PJ's will have the Rainbow Effect because they can only "shoot" one color at a time. They do this by shining the white light from the lamp through a color-wheel that has multiple segments of red, green and blue filters on it; some color-wheels also contain a clear or white filter. There are also 3-chip DLP projectors that do not have the Rainbow Effect because each chip is dedicated to reflect only one color (red, green or blue). These color beams are combined into a single beam that is projected by the PJ.

I just found a very good video clip of how DLP PJ's work. Click on the link below to view it.
http://www.tigerdirect.com/static/html/DLP-Technology-Demo.html


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## Mike P.

Great link! That's what I needed to understand this subject. Thanks.


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## tcarcio

I thought that only some people were suseptible to seeing this and that most people don't. :dontknow:


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## Harpmaker

tcarcio said:


> I thought that only some people were suseptible to seeing this and that most people don't. :dontknow:


Some are more susceptible to it, but I think everyone can see it if they try; after all, I did take a photo of it. :nerd:

It would be interesting if everyone on the forum that has a DLP projector would try it. First (with the PJ on of course), look at your screen as usual, but, keeping your head still and looking at one edge of the screen, rapidly look at the other edge of the screen. The Rainbow Effect should be seen by your peripheral vision. Also try the same thing I did when I took the photo in post #1, just wiggle your finger in the projector beam close to the projector, you should be able to see the effect with your regular vision easily. Make sure you have an image being projected that has more than one color in it.


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## mechman

I'll give it a try Harp!

mech


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## Keith from Canada

Hold the phone for a second here guys...we're talking about a 3x 4 segment color wheel on a high lumens business projector. If you are looking for rainbows, this is definitely the projector to see them on!

Color wheels on HT projectors are much different than the one being used by the OP. They are a minimum of 4x speed and have 6-7 color segments. Finding rainbows on any of these projectors is MUCH more difficult than it used to be. They can be seen by some (very few these days) and certainly aren't something that you can take a still photograph of.

I would emplore everyone to go out and look at a projector designed for HT rather than basing opinions on a Viewsonic projector that did not have HT in mind. The difference is huge.

It is important that people not leave here with a false bias against DLP. This thread makes it sound like everyone will see rainbows on every DLP projector which is simply not the case. Find a modern DLP projector designed for HT and you can stand in front of it all day and wave your fingers and fire your eyes from corner to corner and only a very small percentage of the population will see rainbows. Of those that do make them out, an even smaller percentage will be bothered by them.


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## mechman

Well I attempted to see them last night and I didn't. I'm not saying that they're not there either though. Keith brings up an interesting point as well. I had no idea you were using a presentation pj Harp. 

I have had literally hundreds of different people over to the house since I built my theater and I have never had anyone mention anything about the rainbow effect. I'll try the finger test tonight if I cannot get Vista working right for my gain tests.

mech


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## Harpmaker

mechman said:


> Well I attempted to see them last night and I didn't. I'm not saying that they're not there either though. Keith brings up an interesting point as well. I had no idea you were using a presentation pj Harp.


That's great! 
I didn't know I had a presentation PJ either, although I suspected it; and as I said in the first post, I don't see the Rainbow Effect when watching a movie unless I REALLY try, by doing the fast eye movement. Normal eye movement that includes turning your neck a bit doesn't show the effect.



> I have had literally hundreds of different people over to the house since I built my theater and I have never had anyone mention anything about the rainbow effect. I'll try the finger test tonight if I cannot get Vista working right for my gain tests.


Totally off-topic, but if you do get Vista working for the gain tests, could you take a spectral reading with your PJ shooting separate white, red, blue and green images (like those on the DVE DVD)? As you know, my spectro can't do that.


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## Guest

I can see them if I really try on my Samsung SP-710AE, but again, I have to really try by darting my eyes all over the place. I've never seen them in normal viewing.

Just FYI.


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## drdoan

I had my Optoma for months before I saw any rainbow effect. I also had to dart my eyes back and forth very fast to even see a glimse of it. Under normal viewing, I never see it, just a great picture. 

As a side note: my projector's bulb now has over 5060 hours on it!

Dennis


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## Mike P.

> As a side note: my projector's bulb now has over 5060 hours on it!


Isn't there a chance of the bulb exploding if it has too many hours on it?


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## drdoan

I haven't heard of one exploding. If it does I will let you know. Dennis


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## fibreKid

I see rainbows when I watch the credits at the begining/ending of a program. Usually during a movie I won't though. It does look fairly close to the example. Depending on the color wheel colors the rainbow will change. :nerd:

Also if I'm watching a black and white movie and someone has a suit that is a fine plaid, I'll also the pattern with a pinkish green hue. Drives me nutts.


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## Philnick

The easiest way to avoid the rainbow effect with a DLP projector is to use a non-reflective screen. 

I've been using a Dell 3100 MP XGA DLP projector sold by Dell as a presentation box - the 3100MP - for six years. In my 15' square theater, it throws an image 7' wide by 5'3" high. It handles whatever format it gets through its component cable (which plugs into a DVI jack) - I feed it 480p SD DVD from my Denon 2910, 720p or 1080i from the HD cable box, and - into its S-Video port - fuzzy 480i from my Mitsubishi VHS-HiFi deck (but only under duress!).

With my first screen, highly-reflective drymount board, I saw rainbows frequently. 

Within weeks, I switched to the bare wall, spackled smooth and painted with flat white household paint from the hardware store, and haven't seen a rainbow since.

For extra snazziness, thick black cardboard ("chipboard" from an artists supply store) on the wall hides the gray frame the projector puts around the image, since black lit up by dim gray is still black!


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