Casting a New Image
Front projectors have come a long way in a fairly short time. It wasn’t long ago that we were installing hundreds of pounds of CRT, and spending hours (days?) making them look good.
Thanks to the rapid development of DLP (and LCD and LCOS), projectors now look great, and are cheaper, easier to maintain, and easier to install. But there is still a resistance among many consumers to installing a projector. Knowing the ins and outs of projector technology can help you sell more, and get a hesitant customer a display that they will truly love.
Most high-end projectors are based on Texas Instruments’ DLP, or Digital Light Processing. At its core is the DMD, or Digital Micromirror Device. Most home projectors now are 1080p, and, as such, the DMD has 2,073,600 tiny mirrors, each mirror representing one pixel on screen (1,920 by 1,080). This is unlike DLP rear-projection TVs, where each mirror represents more than one pixel on many displays.
The way this works is a light source (the lamp) is focused on the DMD. The mirrors pivot, and either shine the light through another set of lenses and out to the screen (an “on” pixel) or away (an “off” pixel). These mirrors pivot back and forth very rapidly; hundreds of times per second.
The intensity of the light on screen is determined by how often the mirror shines toward it. In other words, if you want a bright pixel, the mirror shines toward the screen many times per second. If you want a dark pixel, it pivots away from the screen most of the time. If you want a medium gray, then it shines part of the time toward the screen and part of the time away.
This is just a black-and-white image, though. There are two ways to create color. A single-chip DLP (as in one DMD) uses a color wheel. This is just how it sounds. It’s a small wheel with color filter segments. This spins in the light path between the DMD and the lamp. To create red on the screen, the mirrors only shine toward the screen when the red filter is between the lamp and the DMD. The full spectrum of color is created sequentially. So at any given moment, there is only one color on screen. Your brain blends these sequential colors together so you see a full-color image.