The need for a bias light diminishes as screen size increases. The problem with a screen that doesn't completely fill your field of view is that it tends to act like a flash light beam pointed across the room right into your eyes. With larger screens you don't have that large blackness with a small bright light in the middle.
Thanks for that info Chris. I always wondered why I never get a headache watching my projection screen 16 hours a day all weekend when my 56” HDTV would give me problems in just one day. I always thought it was the distance and the fact that I’m loosing my near vision.
