There are many lighting products with different rated power. What is the typical grow light intensity (power per unit area) for edible greens?
Full sun conditions are about 100,000 lumens per square meter. LED and fluorescent lamps produce about 60 lumens per watt which would mean 'burning' about 1.7 kW of electricity per square meter - a fairly astounding number.
However, probably something like 20,000 lumens per square meter would be adequate if the light was tuned to only produce wavelengths adsorbed by chlorophyl - there are 'grow lamps' that are tuned just this way. So, you will need about 350 watts per square meter with LED or fluorescent lamps, maybe a bit more.