Originally Posted by Dr. Purpur
CMH= more PAR per watt. A lot cheaper to run a 630 for the same bang as a 1000 watt sodium.
Your electric bill will be 37% cheaper
I really didn't notice any change in yield when I went from 1000w to 630w of CDM's.
As you say, the electric bill is considerably less. There's also proportionately less total heat to dissipate. I had trouble keeping temps right in hot weather using 1000w but it's easy now, even turning down the fans somewhat. If you run A/C then electric savings there will be proportional, I think. There may be better answers for larger grows but twin 315's in a 4x4 is near ideal for us.
The price & availability of 120v ballasts makes them very attractive for anybody willing to put a little more up front, particularly anybody who has high electric rates. They'll pay for themselves over the first few grows & then it's just more money that stays in your pocket.
I think the high price of genuine philips lamps is offset by their much longer life so that's pretty much a wash. If I replace a 1000w lamp once a year, that's $75. If I replace two philips lamps every two years, that's $75/ year. Same-same.