The Projector Rainbow Effect can be a major annoyance to home theater owners. This is because it can significantly reduce the image quality and make the picture look blurry. In some cases, the projector rainbow effect can even be mistaken for a defect in the projector. The projector rainbow effect is visible on the projection screen as a series of red, green and blue bands that appear to be layered over each other.

In a digital light processing (DLP) projector that uses a single chip, a rotating color wheel in front of the monochromatic light source projects sequential images in different colors rapidly on the screen. The visual system of the observer combines the different colors into one image in the brain producing color motion pictures from a white light source. Unfortunately, the system is not perfect. Some individuals are not able to completely merge the different color images in their mind and individual colors are still perceived creating a “rainbow effect” around high contract images. The effect is made worse if the individual moves their eyes. Speeding up the rotation of the color wheel helps to lessen the effect but does not remove it entirely.

The reason this happens is that moving objects and colors are processed by two different parts of the visual system. The magnocellular pathway processes the movement and position of objects in the field of view and the parvocellular pathway processes the shape and color of objects in the field of view. These pathways begin in the retina eye and continue to the lateral geniculate in the thalamus portion of the brain. The retinal rod cells are more sensitive to movement and the cone cells are more sensitive to color. A slight mismatch in the signals the brain is receiving from the color pathway to the ones being received from the motion pathway lead to a perception of “rainbows”. This effect is similar to a video of someone speaking that is not exactly synced to the audio portion of them speaking.

About 40% of individuals notice this effect. This may be for several reasons; some individual may not pay attention to it, the type of media being viewed may exhibit less of the effect such a lower contrast and slower action, differing eye and brain anatomy that may have different lengths and quality of the magnocellular and parvocellular pathways and increased eye movements in some individuals when watching these projections.