This is really getting to me. I have an Acer PD113 DLP projector 1600 lumens, not brilliant but not expensive. input is Toshiba 340e prog on. My screen is light cream 84" 16:9 diagonal, and the room is totally dark while viewing. Projector normally on ECO mode 1200 Lumen. I've never seen the rainbow effect on my screen. I have seen it on other DLP's but all on bigger screens in less dark rooms. No one else has seen it on mine either so can someone tell me is it to do with an individuals eyesight, the size of the projected image, or a mixture of both?