What is a DLP Video Projector?

A look at DLP technology and its implications for your home theater

DLP stands for Digital Light Processing, a video display technology developed by Texas Instruments.

A variety of video display platforms can use DLP tech, but video projectors use it most. In the past, some rear-projection TVs used it, but they are no longer available.

Video projectors for consumer use that utilize DLP technology project images onto a screen using the following process:

A lamp passes light through a spinning color wheel, which then bounces off of a single chip (referred to as a DMD chip) that has a surface covered with microscopic-sized tilting mirrors. The reflected light patterns then pass through the lens and onto the screen.

DLP Chip, Micro-Mirror, Color Wheel, Light Engine
Images by Texas Instruments and BenQ

The DMD Chip

At the core of every DLP video projector is the DMD (Digital Micromirror Device). This type of chip is structured so that every pixel is a reflective mirror. One to two (or more) million micromirrors are on each DMD, depending on the intended display resolution and the mirror tilt speed control.

As the DMD chip displays the video image source, the micromirrors tilt rapidly as the image changes.

This process produces the grayscale foundation for the image. Color is then added as light passes through a high-speed spinning color wheel and reflects off the micromirrors on the DLP chip as they rapidly tilt towards or away from the color wheel and light source.

The degree of tilt of each micromirror coupled with the rapidly spinning color wheel determines the color structure of the projected image. As the amplified light bounces off the micromirrors, it is sent through the lens and can be projected onto a large screen suitable for viewing.

3-Chip DLP

Another way that DLP is implemented (in a high-end home theater or commercial cinema use) is to utilize a separate DLP chip for each primary color. This type of design eliminates the need for the spinning color wheel.

Instead of the color wheel, light from a single source passes through a prism, which creates separate red, green, and blue light sources. The split light sources reflect on each of the chips designated for each primary color and project onto a screen. This application is costly, in comparison to the color wheel method, which is why it is rarely available for consumers.

LED and Laser

Although 3-Chip DLP technology is expensive to implement, two other, more economical alternatives can successfully eliminate the need for a spinning color wheel.

One method is to use an LED light source. You can have a separate LED for each primary color, or a white LED split into primary colors using a prism or color filters. These options not only eliminate the need for a color wheel but produces less heat and draws less power than a traditional lamp. Increased use of this option has given rise to a category of products referred to as Pico Projectors.

Another option is to employ Laser or Laser/LED Hybrid light sources, which, like, the LED-only solution, not only eliminates the color wheel, produces less heat, and draws less power, but also serves to improve color reproduction and brightness. However, the laser approach is more expensive than straight LED or the Lamp/Color Wheel options (but is still cheaper than the 3-chip alternative).

DLP Drawbacks

Although the "one-chip with color wheel" version of DLP technology is very affordable and can produce outstanding results in terms of color and contrast, there are two drawbacks.

One drawback is the amount of color light output (color brightness) is not at the same level as the white light output.

The second drawback is the presence of "the rainbow effect," which is a brief flash of colors between the screen and eyes when someone rapidly looks from side to side on the screen or glances from the screen to either side of the room. These flashes resemble small flickering rainbows.

This effect does not occur frequently, and many people are not sensitive to it at all. However, if you are, it can be distracting. You should consider your susceptibility to the rainbow effect when purchasing a DLP video projector. Projectors that use LED or Laser light sources are much less likely to exhibit the rainbow effect, as a spinning color wheel is not present.

For a more in-depth technical look at how DLP technology and DMDs work, check out the video from Applied Science.