LCD (liquid crystal display) projectors contain three separate LCD glass panels, one each for the red, green, and blue components of the video signal. Each LCD panel contains thousands (or millions) of liquid crystals that can be aligned in either open, closed, or partially closed positions to allow light to pass through. Each liquid crystal behaves in essence like a shutter or blind, and each represents a single pixel (“picture element”). As red, green, and blue light passes through the respective LCD panels, the liquid crystals open and close based on how much of each colour is needed for that pixel at that moment in time. 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 (or millions) 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 tilt 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 the most expensive DLP projectors, there are three separate DLP chips, one each for the red, green, and blue channels. To define colour, a colour wheel is used that contains (at minimum) a red, green, and blue filter. This wheel spins in the light path between the lamp and the DLP chip and alternates the colour of the light hitting the chip from red to green to blue. The mirrors tilt away from or into the lens path based upon how much of each colour 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.
(Note: In addition to red, green, and blue filters, most colour wheels contain other segments as well. A “white” or clear filter used to boost brightness is common and many colour wheels have filters for colours other than the primaries, such as dark green, cyan, magenta, or yellow.)
More on…
Advantages of DLP ; Disadvantages of DLP ; Advantages of LCD ; Disadvantages of LCD
Abridged from an article by Evan Powell of ProjectorCentral.com