Another video projection technology in common use, both in the home theater commercial environments, is the DLP (Digital Light Processing) projector. Like LCD, the actual image is displayed on a chip, however, the chip used in a DLP projector is different. The chip in a DLP projector is referred to as a DMD (Digital Micromirror Device). In essence, every pixel on a DMD chip is a reflective mirror.
The video image is displayed on the DMD chip. The micromirrors on the chip (remember: each micromirror represents one pixel) then tilt very rapidly as the image changes. This process produces the grayscale foundation for the image.
In a single chip DLP projector, the color is added as light passes through a high-speed color wheel and is reflected off of the micromirrors on the DLP chip as they rapidly tilt towards or away from the light source. The degree of tilt of each micromirror coupled with the rapidly spinning color wheel determines the color structure of the projected image. As the amplified light bounces off the micromirrors, it is sent through the lens and can be projected on a large screen.
On the other hand, in a DLP projector that utilizes a separate chip for each primary color (3 chips total), the light source is split three ways through a prism and reflected off of each chip, and is then sent through the lens onto the screen, instead of pass the light through a color wheel. This method is more expensive because of the use of two additional DLP chips.
Advantages Of The DLP Projector
The advantages of this system make the DLP projector suitable for not only business and home theater application, but DLP technology is also in use in some movie theaters for feature film projection. Basically the films are digitally converted and stored to either to a hard drive or optical disc (similar to DVD - only in High Definition), then fed into the DLP projector and projected onto the movie screen. The high resolution DLP chips made for this application render an image that is almost as good as 35 or 70mm film, without all those film scratches!
Other advantages of the DLP projector include excellent color accuracy, no "screen door" effect(as with LCD), due to its micro-mirror construction, compactness, low power consumption, and high contrast and brightness (although typically not as bright as LCD types but much "smoother" looking).
Limitations Of The DLP Projector
1. Just as with LCD, each DLP chip has a finite number of pixels.
2. Although a DLP projector doesn't exhibit the "screen door" effect of many LCD units, a single chip DLP projector can exhibit what is referred to as Rainbow Effect. This effect is exhibited by a brief flash of colors (like a small rainbow) when the viewer rapidly looks from side to side on the screen or looks rapidly from the screen to side of the room. Fortunately, this does not occur frequently and many people do not have sensitivity to this effect at all. Also, a 3-chip DLP projector does not produce this effect.
3. Just as in LCD projectors, the light source typically must be changed every 3,000 to 4,000 hours. However, just as with LCD-based projectors, new lighting technologies, including both LED and Laser are beginning to make inroads as an alternative. The main stumbling block so far, in addition to initial cost, is that LED light sources, although adequate for smaller room home theater setups can't produce enough brightness for large venue applications.