In all the talk above about lumens, remember that where you place your projector has a lot of impact on brightness. As with most projectors, for any given sized screen, the further back you place the projector, the less bright the image on the screen. This is both an optical design, and a physics thing, so not all lenses behave exactly the same.
In this particular case, there was one unusual aspect. Going from close (wide-angle) to distant placement (telephoto) resulted in a loss of brightness to the tune of more than 50%! That is unusually high, with other projectors sporting lenses similar in range (2:1), more typically around a 40% drop, and some even less.