What kind of light were you using?

I currently use 5w LED grow lights for garden vegetable hydroponics. They are very cost effective. At about 12p/kwh, make it easy and say lights on for 10 hours a day, that would be 1 kwh every 20 days per light, so 12p per 20 days per light.

From what I understand from people who need to also provide heat to their crops, what they save in electricity cost with LEDs, they end up spending in heating costs. So in some cases it can be a bit of a wash