For all of those with a "bat cave", here is a test for you.
1) Zoom your 16:9 projector to be 10% smaller than your screen (so that the left hand side of the screen is not illuminated by the projector).
2) using a calibration disk, put up a window at 100% full white.
3) Measure the brightness of the 100% white. coming off the screen, and measure the light coming off the 10% left hand portion of the screen. This portion of the screen is only lit by reflected light.
4) What is the ratio of the 100% window to the un-illumunated screen.
Note: you may find it difficult to make this measurement, as the light level on the unlit portion of the screen is very low. One way to do this is to take a picture (using an SLR in manual mode, raw picture), making sure not to saturate the picture.
Then use software that reads the pixels in raw linear format (e.g. IRIS free software http://www.astrosurf.com/buil/us/iris/iris.htm
). Convert the Bayer raw pixel values into a 16 bit black and white picture, and compare the 100% white to the 10% left white screen (illuminated by reflections only).
The absolute scale doesn't matter, I'm only interested in the ratio.
I have not done this myself - as my room is hardly a bat cave (I have mid brown walls but a white ceiling). Perhaps I will make the measurement and report back.