In a dark room, I have the PW light set to about 12. If its at max brightness, it is WAY to bright for a dark room.
In bright light, a low setting will essentially look like the light is off...so a high setting they say is better. When I am in a well lit area, I don't use the light so I still leave it at a low setting.
I will sometimes put it on a higher light setting, 20 or so, in a room that is not well lit but is not dark either.