DLP - Single Chip “Rainbow Effect”
No pot o’ gold under this rainbow
Although a DLP projector doesn’t exhibit the “screen door” effect of many LCD units, a DLP projector can exhibit what is referred to as the “rainbow effect”. This visual artifact is best described as brief flashes of perceived red, blue, and green “shadows” observed most often when the projected content features bright/white objects on a mostly dark/black background (the scrolling end credits of many movies are a common example). It is often seen when the viewer rapidly looks from side to side on the screen or looks rapdidly from the screen to the side of the room.
New LED based DLPs can produce the alternating images fast enough so that most people will not be affected by the rainbow effect.The “rainbow effect” is unique only to single-chip DLP projectors. The manufacturers of single-chip DLP projection systems have used color wheels rotating at higher speeds, or with more color segments, in order to minimize the appearance of the artifacts. These are referred to as 2x, 3x or 4x wheels. For example, a six segment wheel (RGBRGB) rotating at two revolutions per frame would be a 4x wheel.
Another way to reduce the rainbow effect is to replace a segmented wheel with a wheel whose colors are in an Archimedean spiral. This forms bands of color that move down (or up) the screen. With segmented wheels, the DMD must “go black” while the wheel transitions from one color to another. Not only can this interfere with persistence of vision and thus accentuate the rainbow effect, it means that the more segments there are, the darker the display will be, all else being equal. The spiral wheel can greatly reduce these effects. The new LED based DLPs are equipped with red, blue and green LEDs which provides both the primary colors and illumination in one device. This eliminates the color wheel mechanism and metal halide lamps required by traditional DLP designs.