around 3000 lumens per square foot(small plants) 6-10,000 lumens per square foot(average size) also depends on how far lights are from plants NOTE;the sun gives out 10,000 lumens on a sunny summers day determine lumens for grow area; determine the square footage of your grow area(example 4 foot by 4 foot= 16 square feet) if you have 1000 watts hps it gives out roughly 107,000 lumens divide by 16=6687 lumens per square foot, so just divide the total amount of square feet and thats your lumens per square foot. lower wattage lights i dont know,lol baked.............