How Many Watts Do You Need Per Square Foot?
Wattage tells you what you pay the utility, not what the plant receives. PPFD is the real number, but wattage is still a useful shortcut when you are shopping.
PPFD targets by stage
Seedlings: 200-400 µmol/m²/s. Vegetative: 400-600. Flower: 700-900, and above that only if you are supplementing CO2. Pushing 1000+ PPFD without CO2 usually just bleaches tops.
Wattage shortcut for modern LEDs
Roughly 30-35 actual watts per square foot of canopy for a full flower run. That is about 120-150W for a 2x2, 300W for a 3x3, and 450-500W for a 4x4.
Read the real wattage
Ignore "equivalent" numbers on the box. Look for actual draw at the wall and, if published, µmol/J efficacy. Anything at or above 2.5 µmol/J is a solid modern fixture.
Frequently asked questions
- Is one big light better than two small ones?
- Two fixtures usually give more even coverage and fewer hot spots in a square tent, but a single well-designed board with good spread is simpler to hang and dim.
Keep reading
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