Good question there isn't much to go on for reference. I use it in my room and a 40w 730nm bar lights up my whole room well and it's 4x9.5x7.5'. I just centered it and let the reflective walls spread it. I also use 630/660nm for 10 minutes before the lights go on (same idea Pr/Pfr on the other end of the light cycle) and 65w lights up the whole room. Just took a camshot of it yesterday before lights on. 730nm is more difficult (for our eyes) to see since it's in the infared spectrum but keep in mind that room is pitch black normally.
630/660nm, 65w
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An older pic of the 730nm 40w bar after lights out...
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Cheers