I'd follow JB NY's statement on reflectors and state that at least in my experience, a good reflector does a LOT. Having pulled off a reflector upgrade from Hamilton flat white metal to PFO parallel a few months ago ... a good reflector will do a lot for you.
I find that there are actually `brighter' areas about 6" in front and 6" in back of my MH bulb now with this new reflector. That the major reflection area is brighter than directly under the bulb ... something new with a good reflector
And if you read the papers by Sanjay Joshi in
www.advancedaquarist.com [SE MH reflectors were March 2003, he did DE reflectors too] - but my `bright zone' experience lines up just about perfectly with his charts.
Never mind the light coverage now blows away what it was before. I never really considered how important reflectors are ... but now I can't help but think about how much light I'm getting out of every bulb watt.