How does a DLP™ projector work? Let’s start with the basics. First, like with all microdisplay technologies, they have a high output lamp that creates white light.
Now white light itself can’t create a full color picture, so there has to be a way of splitting that light into its three primary colors: red, green and blue. DLP™ light engines achieve this by passing the light through a spinning color wheel (see Figure 1). The color wheel is simply a red, green and blue filter that spins in front of the lamp to create the primary colors, one after another.
We now have red, green and blue light. This light is directed to a small silicon chip called a DMD™ device by Texas Instruments (see Figure 2).
The DMD ™ device is a small chip that consists of hundreds of thousands of tiny mirrors that can tilt in two directions, designated as on and off positions, at thousands of times per second. See Figure 3.
Each mirror represents one spot, or pixel, of the image. All of these pixels, when combined horizontally and vertically, make up the entire image. This is much in the same way as your printer makes a printed copy for you.
So how does it make an image? Let’s take that first bit of light that arrives at the DMD™ chip after it passes through the color wheel: red light. At the time the red light strikes the chip, all of the mirrors that correspond to where red should appear within the image will turn “on”. When the pixel is turned “on”, it directs the light out of the lens and to your screen. For the places that contain no red, or no color that is comprised of red, the mirror is turned “off” and the light is then directed away from the lens and to a light collection space within the projector. The DMD™ chip then does the same for the next two colors (blue and green, respectively) in sequence, thereby making up an entire image.
How does the DMD™ create shades of colors that are not pure red, green or blue, and how does it create an image if the red, green and blue are not shown at the same time?
It all has to do with timing. The DMD™ displays shades of red by varying the time it keeps red on the screen. The shorter the time on the screen, the less the eye is able to detect the color, resulting in a lighter shade. It creates colors and whites the same way. Displaying all three primary colors, one after another for the same time period, produces white. If you wish to display a shade of gray, then each color is produced for a shorter time period. To produce colors, the DMD™ will vary the amount of time each color is on the screen to produce different colors at different shades.