Inner Workings: Inside a Front Projector Page 3
The DLP chip - essentially a sophisticated light switch - acts like a field general giving marching orders to a million-strong army of microscopic, hinge-mounted mirrors, which are switched on and off thousands of times a second. The mirrors face the light source when they're "on" and tilt away from it when they're "off." By varying the duration and oscillation of the mirrors, the projector can create up to 1,024 shades of gray, and when used with a color wheel - which spins fast enough so that each of the colors is displayed 60 times per second - color is produced. The color wheel has to be accurately synchronized with the DMD chip so that the colors are displayed sequentially on the DMD at the proper time, creating images with up to 16.7 million colors.
The sequential colors are displayed so rapidly that our eyes see them as a single, full-color image. Sometimes, though, some people can fleetingly see the separate colors - typically as streaks when light-colored objects are displayed against a dark background. To help reduce this "rainbow effect," the wheel spins at a 4x speed (7,200 rpm), so colors are displayed 240 times per second. Since LCD, 3-chip DLP, and current LCoS projectors don't use a color wheel, they're not subject to this effect. Each type of projector has its limitations, however, owing to its respective technology. But that, as they say, is a subject for another "Inside" piece.