Calculate Daily Light Integral (DLI) based on PPFD and photoperiod. Determine how many hours of supplemental light your indoor crops need each day.
Plants don't measure light intensity alone — they respond to the total amount of photosynthetically active light received over an entire day, measured as the Daily Light Integral (DLI) in mol/m²/day. DLI combines light intensity (PPFD, measured in µmol/m²/s) with duration (photoperiod, in hours).
This calculator converts your grow light's PPFD output and the hours it runs per day into a DLI value. Compare that to your crop's DLI requirement to determine if you're providing enough light — or if you need to adjust intensity or photoperiod.
Indoor lettuce needs 12-17 mol/m²/d, tomatoes need 20-30+, and cannabis thrives at 30-45. Low-light herbs like parsley can manage with 8-12. Whether you are a beginner or experienced professional, this free online tool provides instant, reliable results without manual computation. By automating the calculation, you save time and reduce the risk of costly errors in your planning and decision-making process. This tool handles all the complex arithmetic so you can focus on interpreting results and making informed decisions based on accurate data.
Guessing grow light hours leads to either etiolated, stretchy plants (too little light) or wasted electricity and light stress (too much). DLI calculation removes the guesswork and lets you dial in the exact photoperiod for optimal growth and energy efficiency. Having a precise figure at your fingertips empowers better planning and more confident decisions.
DLI (mol/m²/day) = PPFD (µmol/m²/s) × Photoperiod (hours) × 3600 / 1,000,000 Simplified: DLI = PPFD × Hours × 0.0036
Result: DLI = 14.4 mol/m²/day
250 µmol/m²/s × 16 hours × 0.0036 = 14.4 mol/m²/day. This is sufficient for lettuce and herbs but below the optimum for fruiting crops like tomatoes.
Low-light crops (microgreens, lettuce, herbs) thrive at 8-17 mol/m²/d. Medium-light crops (peppers, strawberries) need 18-25. High-light crops (tomatoes, cannabis) need 25-45+. Providing DLI above the crop's saturation point wastes electricity without increasing yield.
Lighting is the largest operating cost in indoor farming, often 50-70% of total energy. LED fixtures deliver 2.5-3.0+ µmol/J (photon efficacy), far better than older HPS lamps at 1.7 µmol/J. Choosing efficient fixtures and optimizing photoperiod saves significant operating cost.
A high average PPFD means little if distribution is uneven. Map PPFD across the canopy at 9-16 points. Aim for a coefficient of uniformity above 0.8 (minimum PPFD / average PPFD). Overlapping fixtures and adjusting height improve uniformity.
Photosynthetic Photon Flux Density — the number of photosynthetically active photons (400-700 nm) hitting a square meter per second, measured in µmol/m²/s. It's the standard for measuring grow light intensity at the plant canopy.
Lettuce: 12-17. Herbs: 10-18. Peppers: 18-25. Tomatoes: 22-30. Cannabis: 30-45. Microgreens: 8-12. Higher DLI generally increases growth rate and yield up to the species' saturation point.
Use a quantum sensor (PAR meter) like the Apogee MQ-500. Budget options include smartphone-based meters, though they are less accurate. Measure at multiple points across the canopy and average for uniformity.
Most plants need a dark period (6-8 hours) for metabolic processes including respiration and starch mobilization. Some crops like lettuce tolerate 20+ hours but rarely benefit from no darkness. 16-18 hours is a practical maximum.
Yes, dramatically. PPFD follows the inverse square law approximately — doubling the distance from the light reduces intensity by ~75%. Keep lights at the manufacturer's recommended height and measure PPFD at canopy level.
Measure natural DLI from sunlight entering your growing area. Subtract from your crop target. Calculate the supplemental PPFD needed: Supplemental DLI / Hours / 0.0036 = required PPFD from grow lights.