Lumen Output, Low Lamp, Bright mode:
GT720 Projector measures: 1941 lumens
That represents a drop of only about 8.5%. Most projectors drop 20-30% in their eco-modes. It would seem the wise thing for most owners to run in eco-mode. That's a small drop in exchange for longer lamp life, and Optoma says the GT720 will get 3000 hours at full power, but 5000 in eco.
Brilliant Color plays a big role in the GT720. With Brilliant Color off, in fact, you have less than 1/3 the brightness of setting it to 10. As Optoma has even Cinema defaulting to 6, I figure they don't expect you to use settings lower than that.