The most common classroom projectors currently being installed in classrooms have XGA or WXGA resolution, and brightness of 2500 to 4000 lumens.
A breakdown of Lumens Output Ratings.
Under 2000 Lumens: This type of rating is used for projectors that are highly portable and produce the lowest light output. This means a projector with this type of rating will be the least expensive as well. It will also require your classroom to be dark in order to provide the best viewing experience.
2000 to 3000 Lumens: A projector with a rating of between 2000 and 3000 lumens is considered to be a standard projector for classroom use. Although the price is a bit higher, this type of device can easily be used in environments with ambient lighting and typically, a totally dark room is not a requirement.
3000 to 4500 Lumens: A projector with a rating of between 3000 to 4500 lumens are ideal for large classroom environments. The rating is high enough to prevent images and videos from appearing faded when used in classrooms with a moderate amount of lighting. The larger images produce better clarity and colors with this type of lumens rating.
4500+ Lumens: A projector with a 4500+ rating is more suited toward an auditorium, stadium, or other type of large venue. This type of projector can range up to 14000+ lumens and contains technology designed for viewing in a space much larger than a classroom. This also makes this type of projector much more costly as well.