Um. Just to quibble.
Certainly not "after a certain point" - placement and distribution is
just as, if not more important as firepower.
A garden under a 600w HPS, 6" off a canopy, is going to receive substantially more light than a 1000w 12" over the same garden.
Here - have a read:
http://en.wikipedia.org/wiki/Inverse-square_law
Yes, after a certain point- that point being the minimum threshold of adequate light provided. after that, you're absolutely right.
I'm well aware of the inverse square law, and something that I was recently taught by Wazzap (who sounds like he works at
Gavita, so I bet he knows his lighting, no?) in another thread recently is that it doesn't begin to apply until distance is 5x the length of the light source. This generally applies more to flourescent lighting, but at the short distance cited in your example it would apply there, too.
Your example was correct- again, to a point. Directly under that light, you're right. However, the 600W light source isn't going to provide that greater intensity to as large a footprint. In fact if it's that close, you're going to get a nasty hotspot and a lot of lanky girls around the edges... to say nothing of what happens 12" below a bare 1000W bulb! Best, then, to try to get the right amount of light as evenly distributed across the canopy as possible. This isn't easy with point sources...
As you can see from this thread, I'm no stranger to the finer points of how lighting works. I'm trying all the cheats in the book, not to mention trying to come up with a few of my own...
Sunshinegrower, I know what you're trying to do, with one each of a HPS and MH bulb in the same fixture. Not a bad plan to get a better mix of spectra on your plants, but again hacking up a raptor isn't going to get you there, not by a long shot! I think your best move is to get a dual element bulb and mount it normally in that fixture and you'll be right where you want to be. If you want to light a 4 x 8 space, then do two of them.
Never quibble with a quibbler... :passingjoint: