The Great Technology War: LCD vs. DLP
December 7, 2005,
(NOTE: This is the seventh update of an article originally posted four years ago. The technologies continue to evolve quickly, hence the periodic updates.)
If you are new to the world of digital projectors, you won't have to shop around very long before discovering that the terms "LCD" and "DLP" somehow refer to two different kinds of projectors. You might not even know what LCD and DLP are before asking the obvious question "which one is better?"
The answer is simple. Sort of. LCD and DLP each have unique advantages over the other. Neither one is perfect. So it is important to understand what each one gives you, so you can make a good decision about which will be better for you.
By the way, there is a third significant light engine technology called LCOS (liquid crystal on silicon). It is being developed by several vendors, most notably JVC, Sony, and Hitachi. Several outstanding home theater projectors have been manufactured with this technology. However the discussion of LCOS technology is beyond the scope of this article.
The Technical Differences between LCD and DLP
LCD (liquid crystal display) projectors usually contain three separate LCD glass panels, one each for the red, green, and blue components of the video signal. As light passes through the LCD panels, individual pixels ("picture elements") can be opened to allow light to pass, or closed to block the light, as if each little pixel were fitted with a Venetian blind. This activity modulates the light and produces the image that is projected onto the screen.
DLP ("Digital Light Processing") is a proprietary technology developed by Texas Instruments. It works quite differently than LCD. Instead of having glass panels through which light is passed, the DLP chip is a reflective surface made up of thousands of tiny mirrors. Each mirror represents a single pixel.
In a DLP projector, light from the projector's lamp is directed onto the surface of the DLP chip. The mirrors wobble back and forth, directing light either into the lens path to turn the pixel on, or away from the lens path to turn it off.
In very expensive DLP projectors, there are three separate DLP chips, one each for the red, green, and blue channels. However, in most DLP projectors under $15,000 there is only one chip. In order to define color, there is a color wheel that consists of (at minimum) red, green, blue, and sometimes white (clear) filters. This wheel spins in the light path between the lamp and the DLP chip, and the filters determine the color of the light hitting the chip. The mirrors tilt away from or into the lens path based upon how much of each color is required for each pixel at any given moment in time. This activity modulates the light and produces the image that is projected onto the screen. In addition to red, green, blue, and white segments, some color wheels now use dark green or yellow segments as well, and we are about to see the introduction of color wheels that contain all six primary and complementary colors--red, green, blue, cyan, magenta, and yellow. According to Texas Instruments, this enhancment, known as "BrilliantColor(TM)", will boost color performance on single chip DLP projectors to new levels. It should begin to appear on new models at CES in January.