Don't confuse projectors with plasmas/lcds.

For projectors the nature is that because light is projected, its best that its viewed in a completely dark room to maximize the effect of contrast. (Even projecting total black in a dark room for the best of projectors, there will be light leakage, so ur iris will close more than u believe).

For plasmas/lcds, its is normally better to use a bias light if ur room is totally dark. The displays are usually smaller and only emit light from the display only. However, there are caveats. It depends on the gamma that u calibrate to and ur environment. It also depends on ur peak light output of the display.

The projectors (even the brightest ones), rarely put out more than 15ft/L. However, the screens are big, so it illuminates a bigger area. If u calibrate ur display to the same, becoz of the smaller screen it will not seem than bright to u. Plasmas/LCDs comfortably hit 30-50ft/L while maintaining accuracy. With the image being so bright, and if the surroundings are dark, it is possible that u could lose some shadow details if u calibrate to the wrong gamma. A bias light and proper peak light calibration coupled with an appropriate gamme setting would yield the most pleasing picture.