The Viewsonic is another projector best suited for movie watching, or smaller screens, say up to 100" diagonal, maybe a bit larger. With a below average 453 lumens in "best" mode, it's still pretty respectable, as many projectors are right around 500 lumens. In brightest mode though, it's 922 lumens are on the low side as well. In other words, not a lot to spare if you want say a popular 110" diagonal screen size. You might have to supplement with a higher than normal gain screen.
The Viewsonic Pro8100 projector, when it comes to brightness characteristics, most closely resembles another LCD projector, the Panasonic PT-AE4000, whos comparable measurements are within 25 lumens of the Pro8100. Note I have always considered the popular PT-AE series from Panasonic to be definitely below average when it comes to brightness, perhaps my biggest complaint about an otherwise excellent projector.