Some answers to previous questions:
1. It helps to have a dark room and a good relecting screen, similar to the kind used for powerpoint presentations. A plain white wall works fine though. A textured finish and an off-white paint, which is what I have, cause further degradation. However, it is still quite viewable, even during the day, with the blinds drawn. A bright projector helps; about 800 lumens is the threshold for acceptable viewing in these conditions.
2. There is a trade-off between brightness and image size (inverse square law). You can get a brighter image with a smaller image size. If you have projector with a zoom lens, this tradeoff still exists, but there is more loss in the lens system (a few % is lost at every air->glass and glass->air transition that the light beam encounters. Sorry, can't do anything about it, even with perfectly clean surfaces, because this is governed by the fundamental laws of optics; specifically, Maxwell's Laws.)
Projector manufacturers try to overcome this by using brighter lamps, which also contributes to a heat problem.
3. A major breakthrough in lamp design occurred in 1998 or thereabouts, with the development of specialized lamps meant specifically for video and data projectors. This is the Osram P-VIP high-pressure mercury-vapor short-arc discharge lamp. Almost all new projectors with lamps in the 100 W to 250 W range (about 95 % of the market) have switched to P-VIP. The remaining are high-power professional and mini-theatre units costing upwards of $50k - $100k, and these still use Xenon arc lamps.
P-VIP has the advantages of small size; a point source (less than 1 mm cubed) of intense white light; long life of typically 2000 hours lamp half-life; and the possibility of introducing dopants in the mercury vapor that compensate for the color transfer characteristics of the intervening glass, mirrors and color-wheel filters in a DLP projector, so that the net result is close to pure white on the screen.
In answer to O2U2's concern about the high cost of the special halogen bulb (most likely metal halide), I would recommend trying to mod the unit to use a P-VIP lamp when the present lamp dies. The P-VIP lamps are no less expensive when bought at retail as direct replacements for specific projectors, around $300-$500. However, the internal bulb and reflector module is manufactured in only a limited number of types; and these can be obtained for about $90 and transplanted into the old lamp unit housing without too much difficulty (this is a racket similar to inkjet cartridges).
The voltages and currents used by the P-VIP lamp (typically 80v at 2A) are likely to be very different from a tungsten metal halide lamp (typically 12v at 10A), and the drive circuits and protection circuits will have to be modified. It's worth investigating, though; the 2000-hour half-life is a big advantage of P-VIP lamps.
4. IMHO, DLPs are better than TFT LCD projectors for a few reasons: they're more uniform in brightness, end-to-end; their contrast is higher; and they have less-stringent cooling requirements, so they can be used with brighter lamps for longer durations with reduced heat duress.
5. The homebrew LCD projectors, while interesting projects, will probably not be comparable in peformance to typical off-the-shelf units, primarily because of the engineering issues connected to the lamp, cooling and optics. The brightness of the the homebrew units is likely to be low, of the order of 200~400 lumens or less, which is probably acceptable at night.
