 these ultra short throw projectors sit inches away from the wall just underneath the screen the benefit of this is because the light has a shorter distance to travel it's also laser light so because the light has a shorter distance to travel you get a brighter screen you don't have to turn all the lights off in the room in order to see the image and because it's laser it's brighter and it will last up to 20 000 hours versus an overhead projector that you be lucky if you get