The ones I have been looking at use three separate monochrome LCD's and one panasonic unit has almost no screendoor effect. I am getting the feeling these homemade ones use full color lcd's designed for laptops and hand-held devices. Is that correct? And if so, is there not a resolution hit?
Actually, they use 13"-15" (some are using up to 19" 16:9 with aspect ratio) desk top LCD screens with full resolution - SVGA - XVGA. We use extremely high quality fresnel lenses, and a high quality triplet projection lens. The LCD screens are stripped of the backlights. Some project makers are building miniature projectors using 7" SVGA screens with. Most commercial home projectors are VGA 800 X 600 rez. Laptops can be used but they have Flat Flexible Cable issues that make them less than ideal.
The images project excellently, and are slightly defocused internally (not noticeable) to eliminate any possible screen-door effect. The 400W lamps produce 32,000 to 40,000 Lumen, which results in a projected image between 1100 - 1600 lumen depending on the number of elements used in the projector (the LCD screen and its polarized filters absorbs 80%).