Simple guide to help you chose the right projector
This is something very important for a projector. Lumens measure a projector's brightness. The bigger this value is the more light the projector will throw.
Larger screens will need a higher lumen projector.
Ambient light is an important factor when you choose a projector. The more ambien light the more lumens you will need in your projector in order to see the image with enough strengh.
To be practical: For an indoor presentation with a screen of up to 80 inches wide (2 m.) and not very strong ambient light a 3000 lumens projector is more than enough.
No, lumens do not affect the image quality. Image quality is related with resolution and contrast.
As each manufacturer can measure the brightness of its projectors using a different method a stardard was defined. This allows us to compare projectors from different manufacturers. This standarization was defined by the American National Standards Institute.
More information about Lumens in the Wikipedia.