How much lighting are you talking about? Obviously, you would not want the main lighting on full blast in the same room. Now, if you have a little ambient lighting on say in the back of the room somewhere you should be fine.
For ex, sometimes I'm shooting a game of pool on the opposite side of my recroom while enjoying a DVD concert and it is fine. The more lighting you have on near the screen/HT area the more the picture can be altered.
These are HT projectors, not presentation (power canon) projectors like you might find at business meeting rooms. This is not something that affects just Sanyo projectors, but all HT type projectors.
The Z5 has some more output than my Z2, so I'm sure you will be fine, just don't crank up all the lights, or use a dimmer.
