What is the difference between models of overheads?
Projection type: There are two different types of overhead projectors transmissive and reflective. Reflective type overheads will not work for LCD projection. Lumens : Lumens is probably the biggest factor in buying an overhead 4 thousand lumens is generally considered the minimum lumens for a overhead more lumens means a brighter image and having more ambient light allowed. Bulb : Most cheaper overhead projectors use halogen bulbs these are somewhat bright but do not produce the lumens or color tempature that metal halides do. Plus halogens run very hot. Premium overhead projectors use metal halide bulbs these bulbs run cooler,produce better color tempature, more lumens and last longer then halogens. But they also cost more per bulb and require a ballast to run. Some metal halide projectors produce as much as 10,000 lumens!
