DLP® projectors
Last updated: January 7, 2009.
Have you ever used a mirror to send a light signal to a friend some distance away? The basic idea is simple: you angle the mirror so it catches light, then tilt it slightly so the light travels where you want it to go. By tilting the mirror back and forth, you can send precise light pulses of either long or short duration—and transmit complex messages using something like Morse code. The latest projection TV system, called DLP® (digital light processing) technology, works in almost exactly the same way. Let's take a closer look!
Photo: A Christie Mirage 5000: a typical modern DLP TV projector. Photo by courtesy of Dave Pape, published on Flickr under a Creative Commons Licence.
What is DLP® technology?
Developed in 1987 by Texas Instruments scientist Dr Larry J. Hornbeck, DLP technology is based on an amazingly clever microchip called a digital micromirror device (DMD). A DMD chip contains about two million tiny mirrors arranged in a square grid. Each mirror is less than one fifth the diameter of a human hair, and it's mounted on a microscopic hinge so it can tilt either one way or another. A bright lamp shines onto the DMD mirror chip and an electronic circuit makes the mirrors tilt back and forth. If a mirror tilts toward the lamp, it catches the light and reflects it off toward the screen, creating a single bright dot of light (equivalent to a pixel of light made by a normal TV); if a mirror tilts away from the light source, it can't catch any light, so it makes a dark pixel on the screen instead. Each mirror is separately controlled by an electronic switch so, working together, the two million mirrors can build up a high-resolution image from two million light or dark dots.
Photo: The Texas Instruments DLP® processor from inside a modern TV projector. Photo by courtesy of Collin Allen, published on Flickr under a Creative Commons Licence.
To make color images, DLP projectors need an extra bit of technology: they have a spinning colored wheel inserted into the light path, which can color the pixels red, blue, or green. Combined with the tilting mirrors, the color wheel makes a front-projected TV picture from millions of pixels of every possible color.
