The first generation DLP projectors incorporated a colour wheel that rotated sixty times per second, which can be designated as 60Hz, or 3600 RPM. With one red, green and blue panel in the wheel, updates on each colour happened 60 times per second. This baseline 60Hz rotation speed in the first generation products is also known as a "1x" rotation speed.

Upon release of the first generation machines, it became apparent that a small but vocal percentage of the population were experiencing headaches from either seeing colour breakup more commonly known as the "Rainbow Effect" or from the sequencing of the colours. One point that must be considered with public projection systems using single chip DLP projectors is the possible effect on Epileptics. Although not visible to the naked eye the rapid flashing Due to the sequencing of colours produced by the single chip system, has been noted to make some epileptics feel ill.

To counter this effect in the second generation DLP projectors, the rotation speed was doubled - referred to as 2x Speed (120Hz, or 7200 RPM). The doubling of the refresh rate reduced the margin of error, and so reduced the visibility of rainbows. It also reduced the number of people who could detect the rainbows at all.

Today, many DLP projectors being built for the home cinema market incorporate a new six-segment colour wheel which has two sequences of red, green, and blue. This wheel still spins at 120Hz or 7200 RPM, but because the red, green, and blue is refreshed twice in every rotation rather than once, the industry refers to this as a 4x speed. This further doubling of the refresh rate has again reduced number of people who can detect them visibly. Yet there is still a small fraction of the population who are sensitive to them.

Two things that is critical to the reduction of the rainbow effect is the timing of the projected image through the colour wheel, This varies from manufacturer to manufacturer and the number of segments in the wheel and the number and order of the colours in the wheel.

To see the rainbow artifacts spread your fingers and wave your hand in front of your face while watching a DLP image or move your eyes (see diagram 1) quickly from left to right as if watching a Tennis match. Picture 2 shows a bad case, this is created from the projection of a single white circle and using the eye movement technique. For those of you that don't have the classic white circle DVD, picture 3 shows an example of when the rainbow effect is most visible compared to an LCD projector. Are you sensitive to the Rainbow Effect? click here to take our eye test.

Diagram:1

Pic: 2

Pic: 3