How the Color Wheel on a Projector Works

Digital light processing technology has become an extremely popular option for business and home theater projectors. The technology uses a chip with microscopic mirrors that flick on and off multiple times per second to either divert light through the lens and onto the screen or divert it away from the lens, leaving that area dark. Color wheels come into play on one-chip DLP projectors which are, by definition, monochrome devices.

In a one-chip DLP projector, all that the chip can do is either send or not send light – making it black-and-white only. To create color images, projector manufacturers include a color wheel which rotates in synchronization over the DLP chip. As it rotates between red, blue and green, the DLP chip sends the correct pattern of light. Because the images go on and off the screen so quickly, the brain puts them together into one full-color image. This is similar to how the brain perceives the series of still images in a movie as an actual moving picture.

Running a DLP projector's light through red, green or blue filters has the effect of slightly dimming the picture. To solve this problem, some color wheels have an additional clear segment which lets the projector's bulb shine through and increase the brightness of the image. Because doing this can also wash out the image and make it less colorful, some color wheels include extra segments with non-primary colors like yellow or magenta.

The key drawback of the color wheel is the "rainbow effect." While most people perceive a DLP image as being of continuous tone, some people's brains actually see the different colors being projected separately. This can be especially noticeable where white and black meet – like with a projected spreadsheet of black text on a white background. In an attempt to alleviate this problem, some manufacturers speed up the color wheel, making each individual color show up more times in a second for a shorter period of time. This can make the "rainbow effect" less visible for many people.

There are two popular alternatives to projectors with color wheels. The first is to use a DLP projector with three chips – one for each color. These projectors have excellent image quality and no rainbow effect, but are both bulky and expensive. The other alternative is a projector that uses liquid crystal display technology. These projectors offer better color accuracy and brightness than many DLP projectors, but are sometimes larger and may also have slightly lower contrast.