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LCD vertical banding or DLP rainbows?

Evan Powell, May 24, 2005

DLP rainbow artifacts

DLP projectors have no vertical banding problems. But all of the inexpensive models (okay, say, those under $15,000) have a single DLP chip and a spinning color wheel that can produce visible color separation artifacts-commonly known as rainbows. People tend to perceive rainbow artifacts differently based upon how sensitive they are to them. But basically, they appear as a breakout of red, green, and blue color that shouldn't be there. When you see momentary splashes of color in Casablanca, you know something's not quite right. Not only are they visually distracting, but sequential color updating from the spinning color wheel can cause eye strain and headaches for many viewers. This problem never occurs on an LCD projector because LCD projectors don't use color wheels.

Some people are never bothered by DLP rainbows. I am one of them. I can watch a DLP projector all day long and never see visual distractions or develop eyestrain or headache. This is somewhat of a handicap for a projector reviewer. In years past I'd give a particular DLP projector a glowing review, only to get a flurry of email saying, "Evan, are you nuts? There are rainbows everywhere."

Individual sensitivity to rainbow artifacts can vary greatly. In addition to folks like me who don't see them at all, there are those who notice them from time to time, but don't find them to be much of a nuisance. On the other hand, there are some who are so bothered by them that they cannot watch a DLP projector under any circumstances.

In today's market, most business class DLP projectors have what is known as a 2x speed wheel. Many units designed for home entertainment have 2x wheels also. It is the 2x wheel that causes the most problems.

Texas Instruments and the manufacturers of DLP projectors have increased the speed of the sequential color updating in order to reduce the percentage of the population that is affected by rainbow artifacts. By using a different wheel design that uses two sets of red, green, and blue filters instead of one, the manufacturers are able to double the refresh rate on the screen. This wheel design is referred to as a 4x wheel, and it substantially reduces the number of people who are affected by rainbows. Our newest staff reviewer, Bill Livolsi, has trouble watching 2x DLP projectors for any length of time. But he has no problem at all with the 4x models.

These days we often stipulate in reviews of DLP projectors that rainbow artifacts are a potential hazard of the technology. Though the faster wheels speeds have substantially reduced the percentage of the population that is susceptible to rainbows, there are still those who find them a problem even at the fastest wheel speeds.

The bottom line is I personally would not use a DLP projector with anything less than a 4x wheel in my own theater. Even though I am not bothered by rainbows, I expect that others besides me will be using my theater, and I would not want the system that I am so proud of to be giving them headaches.

Furthermore, even entry level DLP projectors like the Optoma H31 and the InFocus Screenplay 4805 feature 4x wheels. These units are selling for a mere pittance these days. Now that street prices of these outstanding 4x DLP projectors have fallen to their current level, we no longer recommend any DLP projector with a 2x wheel for home theater applications.

Just as with the LCD vertical banding issue, you need to buy a DLP projector from a dealer that will grant you a favorable return and exchange policy. You must fire it up and audition it for at least two hours with everyone in your household who will be frequent users of the projector. The faster wheel speeds reduce but do not eliminate the possibility that you may experience visual distractions, eyestrain, or headaches. So give everyone a couple of hours of exposure to ensure that nobody is adversely affected. And you might try it with a classic B/W film like Treasures of the Sierra Madre or Casablanca for the ultimate test, since color artifacts, if you are prone to see them at all, will be most apparent on black and white material.

The bottom line is that LCD and DLP projectors can both exhibit flaws that impair the viewing experience. So be aware of the potential issues, and buy from dealers with favorable return policies and good reputations for customer service. By doing so you'll eliminate the risk of having LCD vertical banding or DLP rainbow problems on your home theater projector.

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