Color Wheel DLP Color Wheel (single-chip sequential color)

What a color wheel is

A color wheel is a disc split into sectors, each coated to pass one band of color, that spins in front of the light source of a single-chip DLP projector. Wikipedia lists the primary sectors as red, green, and blue, often with a white (clear) sector, and newer designs that replace white with cyan, magenta, and yellow. Christie describes the single-chip arrangement as one DMD and a color wheel generating color, where white light "passes through a rapidly spinning color wheel that contains red, green, and blue filters." The DMD is the Digital Micromirror Device that holds one mirror per pixel, with a Full HD chip carrying 1,080 rows of 1,920 mirrors, about 2.07 million in all.

How a color wheel works

The projector shows one color at a time. The DMD flips its mirrors to build the red part of the frame while the red sector is in the beam, then the green part, then the blue part. Run fast enough, the eye blends the sequence into one full-color image. ProjectorCentral's explanation of the generations gives the speeds: first-generation DLP wheels turned once per frame, or 60 times a second; second-generation wheels doubled it to 2x, which is 120 revolutions per second or 7,200 RPM. Wikipedia says most current systems run at up to 10 times the frame rate.

The arithmetic is simple. A 4-segment RGBW wheel at 7,200 RPM sweeps 120 x 4 = 480 sectors per second, about 2.1 ms each. A six-segment RGBRGB wheel at the same 7,200 RPM sweeps 720 sectors per second, about 1.4 ms each, and repeats every primary 240 times a second, which is four times per 60 Hz frame. That is why ProjectorCentral calls a six-segment wheel at 120 Hz a 4x effective rate. BenQ says high-end DLP home theater projectors typically carry six-segment RGBRGB color wheels, and lists RGB, RGBRGB, RGBW, RGBCMY, and RGBCWY as the common layouts. ViewSonic's first RGBRGB model was the Pro7827HD, and its PJD7828HDL uses a six-segment RGBCYW wheel.

Color wheel vs three-chip DLP vs RGB laser

Three-chip DLP uses a prism and one DMD per primary, so it has no wheel and no rainbow effect. The single-chip RGB laser alternative fires the red, green, and blue diodes in sequence instead of spinning a disc. BMC AV puts the sequential rate in the kilohertz range, ">10,000 Hz," with each color getting about 33% of the time, and rates a three-chip layout as often 20 to 40% brighter for the same laser power because all three colors run continuously. Wikipedia explains the reason a wheel can go: LEDs and lasers have pulse rates not limited by physical motion.

The wheel is not just an old part. Christie says laser-phosphor projectors use blue laser diodes aimed at a phosphor wheel that produces red and green, and that advanced versions add a direct red laser diode to boost low red output. It quotes up to 20,000 hours to 50% brightness for laser phosphor DLP and 25,000 hours for RGB pure laser, up to 50,000 lumens for RGB pure laser, and 98% of Rec. 2020. A phosphor wheel is a different part from a color wheel, and the sources I fetched do not say which models keep both. Check the spec sheet. See laser phosphor and RGB triple laser.

The rainbow effect

Because only one color is on at any instant, a fast eye movement across a high-contrast edge can land different colors on different parts of the retina. Wikipedia describes "brief flashes of perceived red, blue, and green shadows." ProjectorCentral says most people cannot detect the artifact at all, while the most sensitive viewers find it distracting enough to make the picture unwatchable, and that the six-segment, two-set RGB design substantially reduced the number of people who see it. Faster wheels, more segments, and sources that skip the wheel are the mitigations. For the full artifact write-up see rainbow effect.

What to check in a spec sheet

Look for the segment layout (RGB, RGBW, or RGBRGB), the speed multiple (2x, 4x, higher), and whether the projector is lamp, laser phosphor, or RGB laser. ViewSonic says its RGBRGB wheel covers 100% of Rec.709, and BenQ rates its DLP chip for over 100,000 hours, so the layout and the chip are separate questions. With an RGB laser engine the wheel disappears entirely. Brightness comparisons belong in ANSI lumens, and the DLP entry covers the chip itself. The lamp vs laser tool and projector lumens tool help with sizing.

Common confusions

More segments do not by themselves mean more brightness or a wider gamut, and layouts such as RGBW, RGBCMY, and RGBCWY exist because makers trade color against light output differently. Rotation speed also is not the same as segment count: a six-segment wheel at 7,200 RPM and a three-segment wheel at 14,400 RPM would flash the same number of sectors per second but split the colors differently. Finally, the wheel is only one of three architectures: Christie lists single-chip, three-chip, and the laser variants, and the three-chip option removes the sequential-color artifact while BMC AV credits it with extra brightness.