DLI Calculator — Daily Light Integral
Calculate Daily Light Integral from PPFD and photoperiod, or solve for the PPFD or photoperiod needed to hit a target DLI. Compare against crop-specific targets by growth stage and estimate lighting energy costs.
What Is DLI?
Daily Light Integral (DLI) measures the total number of photosynthetically active photons delivered to a crop over a 24-hour period, expressed in mol/m²/day. Unlike PPFD (which measures instantaneous light intensity in µmol/m²/s), DLI captures the cumulative light dose — the metric that actually determines crop yield, quality, and morphology. DLI is the product of PPFD and photoperiod: DLI = PPFD × photoperiod (hours) × 0.0036. Most leafy greens need 12–17 mol/m²/day, herbs 15–22, and fruiting crops 20–30. Exceeding the target wastes energy; falling short limits yield.
How to Use This Calculator
- 1 Choose your solve mode: find DLI from known PPFD and photoperiod, find the PPFD needed for a target DLI, or find the photoperiod for a target DLI.
- 2 Enter your known light parameters. The calculator solves for the missing variable in real time.
- 3 Select a crop and growth stage to compare your DLI against its optimal range.
- 4 Set your LED efficacy, electricity rate, and grow area to estimate lighting energy costs.
DLI Targets by Crop & Growth Stage (mol/m²/day)
| Crop | Overall Range | Propagation | Grow-out / Veg | Harvest / Fruit |
|---|---|---|---|---|
| Butterhead | 12–17 | 8–10 | 14–17 | 14–17 |
| Romaine | 14–18 | 8–10 | 15–18 | 15–18 |
| Leaf Lettuce | 12–16 | 8–10 | 13–16 | 13–16 |
| Basil | 15–22 | 8–12 | 18–22 | 18–22 |
| Arugula | 12–16 | 8–10 | 12–16 | 12–16 |
| Kale | 14–20 | 8–10 | 16–20 | 16–20 |
| Microgreens | 8–14 | 0 (blackout) | 10–14 | 10–14 |
| Strawberry | 18–26 | 14–18 | 20–24 | 22–26 |
| Tomato | 20–30 | 15–18 | 22–28 | 25–30 |
| Cucumber | 18–28 | 14–18 | 20–25 | 22–28 |
Frequently Asked Questions
What is the difference between PPFD and DLI?
PPFD (Photosynthetic Photon Flux Density) measures the instantaneous intensity of photosynthetically active light in µmol/m²/s — like measuring water pressure from a hose. DLI measures the total accumulated light over 24 hours in mol/m²/day — like measuring total gallons delivered. Two farms can have the same DLI with different PPFD and photoperiod combinations.
How much DLI does lettuce need?
Most lettuce varieties perform best at 12–17 mol/m²/day during grow-out. Butterhead is on the lower end (12–17), while romaine needs slightly more (14–18) for dense heart formation. During propagation, 8–10 mol/m²/day is sufficient. Exceeding 20 mol/m²/day for lettuce wastes energy and can cause tip burn.
How do I calculate DLI from PPFD?
DLI = PPFD × photoperiod (hours) × 3600 / 1,000,000. For example, 250 µmol/m²/s for 16 hours = 250 × 16 × 3600 / 1,000,000 = 14.4 mol/m²/day. This calculator handles the conversion automatically.
What LED efficacy should I use?
Budget LED fixtures run around 2.0 µmol/J, mid-range around 2.5, premium around 2.8, and top-shelf fixtures exceed 3.2 µmol/J. Higher efficacy means less electricity per mol of light delivered. Check your fixture spec sheet for the PPE (Photosynthetic Photon Efficacy) rating.
Does higher DLI always mean higher yield?
Not necessarily. Each crop has a saturation point beyond which additional light provides diminishing returns or causes stress (tip burn, bolting, bleaching). The goal is to hit the optimal DLI range for your crop and stage — not to maximize it. The energy cost of the last 10% of DLI often exceeds the yield benefit.
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