ELEKTOR FORUMS

This is an excellent article. However,here are a few points that could do with further clarification.

The purpose of the light tunnel is to extend the effective focus of the ellipitical reflector of the lamp. It does this by mutiplr reflections so thst the light coming out of the light tunnel appears as though it is directly coming from the lamp.
The lamp reflector has two focus points, one at the location of the arc in the lamp and the other at the colour wheel. With a small spot of light at the colour wheel the time taken for this spot to cross the colour boundaries is small. During this time of crossing the DLP chip is turned off.
Hence the time that any colour is active is less than that shown by the segment of the colour wheel. Not by much but it could be used to improve the thermal efficiency of the LEDs by having them turned on for a slightly smaller time than the 2/7 in the text.

Note that a lens could have been used instead of the light tunnel with the focus of the lens at the light spot on the colour wheel. The output of this lens would then be a parallel stream of light which would use another lens to present the light onto the DLP mirrors and then to the projection lens.

The arrangement of LEDs used is very inefficient with regard to the amount of light that actually reaches the screen. The term used for the proportion of light that actually comes out of the projection lens is entendue. So here the entendue would be low.
It would be much better if individual lenses are used for each LED with the focus of each of those lenses at the LED surface. A matrix of hexagonal lenses can easily be made from filing down the sides of plastic lenses into a hexagon and then gluing them together - which I have done. The output of this matrix will be a parallel beam of light. Note that this cannot be achieved with just one lens.

This creates another problem. The light beam is now much larger in width and height, even with lenses of very short focal length. And the LEDs have to be much further apart on the heatsink. The size of the lenses and the spacing for the LEDs depends on the angle that the light is emitted from the LEDs. For the Luxeon Rebels this angle is 140 degrees so a very short focal length lens is needed to minimise the diameter of the lens used. As an example let's say that the lens for each LED that we have has a focal length of 10mm, then the diameter of the light spot from the LED at 10mm from the LED will be 55mm (2x tan (140/2)x 10).

To explain the rest would need a full article in itself, especially how to fit this now large sized light source into the projector.