Projectors generally divided into three types, long-throw projector, short-throw projector, and ultra-short-throw projector. The difference is they have different throw distances, which are the length of the light from the lens to the interactive whiteboard
. The long-throw projectors are relatively cheap due to low lens manufacturing costs, which are generally use in large venues, such as outdoor theater, stadium. As for the short-throw projector, the advantage is that it can show a larger image in a shorter distance, the smaller the distance from the lens to the interactive whiteboard, the lower the probability of people blocking the light. So short-throw projectors are frequently use in the meeting room, classroom, even if at home.