When comparing the power of various grow lights, look at the “actual power draw” or “actual power consumption” in watts. Generally speaking, grow lights should use 32 watts per square foot of grow space at the absolute minimum, though 50 to 80 watts per square foot is ideal.  The actual brightness of LED lights is measured in lumens rather than watts, which is another way of measuring light intensity. Vegetables typically require 2,200 lumens per square foot, while other plants generally need approximately 1,375 lumens per square foot.