The DLP rainbow effect only occurs in single DMD chip DPL projection systems.

In single DMD chip projectors there is a color wheel, commonly containing red, green, and blue primary color sectors, between the projector bulb and the DMD chip. The DMD chip is synchronized with the rotating motion of the color wheel so that the one color component (eg. green) of an image is displayed on the DMD the same color section of the color wheel is aligned in front of the lamp. Red, green, and blue images are displayed sequentially fast enough for the viewer’s eyes combine them into a full color image.

The human eye has a threshold called the flicker fusion threshold beyond which rate intermittent light appears steady. When the rate of sequential images from a DLP projection fall below the threshold for an individual (threshold varies between individuals) the outlines of individual, different colored images can be seen as in the image. This effect is called the rainbow effect. It is most likely to be seen when bright objects are over layed on a dark background or one’s eyes pan across an image. Aside from the visual distraction, the rainbow effect can cause headaches and eye strain.

DLP consumer electronics manufacturers use a number of tactics to combat the rainbow effect including:

• Faster color wheel speeds
• More color segments
• Archimedian spiral sectors on color wheel

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