Do watts from the wall matter? The old rule of thumb was 25 watts per sq ft was the minimum for flower. Now most of the new LED's seem to hit right at that target for flower but they are not much above it. When we measure light at the top of the canopy we dont measure in wattage we measure in PPFD or LUX and raise and lower the lights to hit the target PPFD or LUX balanced across the canopy.
With 2 1000w HID's over a 4 X 8 area I have about 62 watts per square foot, that's over kill but by raising, lowering and tilting the the lights I can maintain a even light canopy at about 40,000 LUX at the top of the grow canopy for Veg and 65,000 LUX through flower from corner to corner. Looking at the SF2000 LED as example in the center at 18 inches above the canopy it has a rating of 974 PPFD in the center and as low as 437 PPFD at the outer edges of the light canopy. In a 2 X 4 tent with the light at 18" the light canopy intensity decreases by over 50% from center to corners. I put a light mover on mine as a test and the light is more balanced but still a long way from a level canopy.
So wattage may play a roll in the PPFD but not as an equal size area.
is it possible to have a flat canopy of light with an LED? If so how?
What are your thoughts on that? Please let me know so I can stop thinking about it.