Ok so lets take this thru a year of use bunkerking. I am going to compare a growers choice ROI-680 to a gavita 1000e DE fixture. The worst of the LED's I would consider using, meaning the least efficient.
So right off the bat we have 320 watts less use per hour for the light. Lets call it 13 hours a day to allow for the 18/6 of veg. So that adds up to 125 Kilowatt a month. For me that is around $ 17.47 a month. But that is not the real killer for me, it is the cooling cost of the light. 1000 Watt HPS with ballast is around 11,000 btu's. Cooling that off takes 12,000 btu AC, that runs at 10 amps but we have the led offset of say 3000 btu's. So we are only using an additional 8000 btu's for cooling. 12,000 btu pulls 10 amps per the spec on home depot. But we are only using 2/3 of that. so 6.7 amps equals .603 kilowatt an hour. times 13 hours x 30 days = 32.92 a month. Together we have 50.39 x 1 year = 604.68.
I can get the Gavita 1000 e DE for $ 360 a unit ROI-680 $ 925 a unit. Difference of $ 565.00, but we saved 604 the first year. So within a year with just one light the cost of use is lower for the LED. But oh wait we have to plug in a new bulb for the 1000 De in there every 6 months so that cost is say $ 150.00. Wait we are actually ahead by $ 189.00 the first year. That is for 1 light, it just keeps adding up from there.