Jargon-buster :: Brightness
Brightness - measured in ANSI lumens - the higher the number the brighter the image. When using a projector in a room with lots of natural light you will need a projector that can generate at least 2500 ANSI lumens. No projector can overcome bright and direct sunlight; only blackout curtains or blinds can do that.
Projector brightness is an feature not to be skimped. It is advisable to have a demonstration of a few projectors; though this may not always be a free service it will help to ensure you have the right type of projector.