Grow light calculator: PPFD, DLI and wattage
How this works
Area (m²) = length × width × 0.0929. Required PPF = target PPFD × area ÷ (1 − losses). Wall watts = required PPF ÷ efficacy. DLI = PPFD × hours × 0.0036. Manufacturer PPF figures are measured in an integrating sphere; real canopies lose light at the walls and edges, hence the loss factor.
Use the result with our best grow light for a 4x4 tent guide.
FAQ
How do you calculate DLI from PPFD?
DLI (mol/m²/day) = PPFD (µmol/m²/s) × hours of light × 0.0036. For example, 700 PPFD for 12 hours is about 30 mol/m²/day.
What PPFD do plants need in flower?
Most high-light flowering crops do well at roughly 600–900 µmol/m²/s without added CO₂; seedlings want 100–300 and vegetative growth 300–600.
How many watts of LED do I need for a 4x4 tent?
At a 750 PPFD target and a 2.5 µmol/J fixture with about 20% losses, a 4x4 (1.49 m²) needs roughly 560 W from the wall. Higher-efficiency fixtures need less.