Grow Light PPFD & DLI Calculator
Enter your light's PPFD at the canopy and your photoperiod to get the Daily Light Integral. See if it meets the target for your plant type and how many hours per day you need. Nothing uploaded.
Light Settings
Daily Light Integral
Learn more: PPFD, DLI, and grow light science
PPFD and DLI - why light intensity isn't enough
Indoor gardeners often know their light's wattage, but plants don't respond to watts - they respond to photons. PPFD (Photosynthetic Photon Flux Density) measures light intensity at a specific moment: how many photons hit the canopy per second (µmol/m²/s). DLI (Daily Light Integral) measures the total dose accumulated over a full day (mol/m²/day). Plants need a minimum DLI to grow well. A weak light on for 20 hours might deliver the same DLI as a powerful light on for 4 hours, but the plants will respond differently.
Plant-specific targets - tomatoes, lettuce, herbs, and more
Each plant type has a minimum and optimal DLI range. Lettuce and leafy greens need 10-16 mol/m²/day. Tomatoes need 20-35 mol/m²/day - more for fruit production, less for vegetative growth. Herbs like basil need 12-15 mol/m²/day. High-light-demand crops like cannabis or peppers need 25-40 mol/m²/day. This calculator includes 10 plant types and shows the target range for each. If your current setup delivers less than the minimum, you need more PPFD or longer photoperiod. If it exceeds optimal, you may be wasting energy.
Calculating photoperiod from PPFD and target DLI
The formula is simple: DLI = PPFD × hours × 3.6. If you want 20 mol/m²/day DLI and your light delivers 400 µmol/m²/s PPFD, you need: 20 / (400 × 3.6) = roughly 14 hours per day. This calculator does that math instantly and shows you the exact hours needed for any plant target and PPFD combination.
FAQ
Can I estimate PPFD from LED wattage?
Roughly - most modern LED grow lights deliver 1-2 µmol/watt. A 200-watt LED at 1.5 µmol/watt delivers about 300 µmol/m²/s at 12 inches distance. But this varies by fixture design and distance. For accuracy, measure PPFD with a quantum sensor or use the manufacturer's spec sheet.
Does running lights 24 hours hurt plants?
Most plants need a dark period to process light energy and regulate growth. Continuous light can stress plants and waste electricity. Even high-light plants do well on 16-18 hour photoperiods at optimal PPFD. The calculator assumes a dark period is needed.
What happens if I exceed the optimal DLI?
Beyond the optimal range, additional light usually produces diminishing returns and wastes electricity. Some plants show photoinhibition (light stress) at very high PPFD. Most indoor setups are light-limited, not light-saturated, so this is rarely a problem in practice.