That depends on what you do with the excess heat from the grow lights. For example, if you were growing vegetables in the basement of your house, the heat from

That depends on what you do with the excess heat from the grow lights. For example, if you were growing vegetables in the basement of your house, the heat from the lights would rise to heat the living space. You'd wind up using more or less the same amount of CO2 as required on heating alone, but you also end up with food to eat.