There have been lots of activity going on in the DIY Projector scene, specially using a design involving a 15" LCD panel, two fresnel lenses, a projection lens and the metal halide light sources. This design can be built for less than $500 easily using all new components to project a bright and very high quality image.
Last year I had helped a few people in constructing DIY Projectors based on the said esign, but I observed a few features that I found annoying. Most of these problems were due to the metal halide lamp, or any type of lamp that dessipates lot of heat. These types of lamps became very popular because they were economical, bright, have a good color output and easy to find. Heat was a problem because most LCD panels would not operate properly above 110F , so fans were needed to cool the projector. The fans in return also creates a problem of their own, sound.
The second major problem I saw was uneven light distribution to the screen, meaning that the projected image had dark corners compared to the center. This was because the lamp was a point light source and distance from the lamp to the center of the fresnel lens was shorter than at the corners.
Because of this, I decided to use something other than a metal halide or equavalant light source that doesn't output much heat, such as LEDs. Only a very small number of people have attempted this before. Instead of using a metal halide lamp as the light source, it would use a array of high intensity directional white LED's as the light source. From calculations I found that using 950 10mm LEDs with 110,000mcd at a 20 degree 50% power spread would be equal to the brightness of a 400W metal halide lamp.
Another advantage of using the array of LED's would be that they would act as a panel of directional light, outputting parallel light into the LCD directly. This eliminates the need for the first fresnel lens to fix the metal halide lamps light rays. Also since the heat outputted by the LEDs are negligible, no cooling is required for the project, making the projector completely silent. Only a AC voltage converter and a few resistors are needed to drive the LED array, eliminating the ballast and the cooling circuitry needed in a conventional DIY projector, plus its much more safe to work with because of lower voltages.
The third advantage is size. Since the LED array is flat and only be at maximum 5 cm, the depth of the projector can be cut in half compared to using a point light source. Cost will stay the same as using a metal halide lamp because that many high intensity LEDs would cost the same as cooling equipment, metal halide lamp, ballast, and a glass panel. I have already recieved my projection lens, and currently waiting the arrival of the LEDs and a LCD monitor. I will update this as I build the projector.