Hello id like to join the conversation with a little about your last question,
Gray screens are also called "high contrast screens" because they intend to boost contrast on digital projectors in rooms that are not entirely dark. The gray screen absorbs ambient light that strikes it better than a white screen does and the black level on the screen is maintained. The Philips lamp is then mentioned by ovadoggvo because if the projector has ample lumen output as a digital projector with a Philips brand lamp, the whites remain satisfyingly white, while blacks are maintained at a deeper black. What the gray screen is intending to do is to increase the contrast range of the image on the screen.
So before making your decision, do you plan to have a dark viewing room, with dark walls, ceilings, furniture, etc? If yes, then your best solution is a white screen with a high contrast projector. However, most home theater installations are not done on a dedicated, fully darkened viewing room. Projection systems are frequently set up in living rooms, family rooms and whole basements with walls in shades of olive green and desert beige! These come along with colored ceilings, drapes, furniture, etc. Thus, even when the lights are fully off, the light being reflected from the screen will bounce off of the reflective elements in the room and back onto the screen. In this situation, a gray screen will be more effective at killing this incident light and thus maintaining deeper black levels on the screen.
Hope this helps you and let us know how your project is coming along, hopefully in time for the Super Bowl XLVIII!