DLI Formula
DLI [mol/m²/day] = PPFD [μmol/m²/s] × hours × 3600 / 1,000,000The 3600 converts hours to seconds, and the 1,000,000 converts μmol to mol.
DLI Targets by Crop
| Crop | Min | Max | Ideal |
|---|---|---|---|
| Lettuce | 12 | 17 | 14 |
| Basil | 15 | 25 | 20 |
| Tomato | 20 | 30 | 25 |
| Cucumber | 18 | 28 | 23 |
| Strawberry | 12 | 20 | 16 |
| Cannabis (Veg) | 25 | 40 | 35 |
| Cannabis (Flower) | 35 | 65 | 45 |
| Microgreens | 6 | 12 | 8 |
| Seedlings | 6 | 10 | 8 |
Values in mol/m²/day. Sources: Faust & Logan 2018, Bourget 2008, USDA CEA guidelines.
Frequently Asked Questions
What is DLI (Daily Light Integral)?
DLI is the total amount of photosynthetically active light (PAR) that a plant receives in one day, measured in mol/m²/day. It accounts for both light intensity (PPFD) and duration (photoperiod). A plant under 600 μmol/m²/s for 18 hours receives a DLI of 38.9 mol/m²/day.
What is the ideal DLI for tomatoes?
Tomatoes perform best at a DLI of 20–30 mol/m²/day, with 25 as the optimal target. Below 15, fruit production drops significantly. Commercial greenhouse tomato growers often supplement with HPS or LED lighting to maintain DLI above 20 even in winter.
What DLI do I need for lettuce?
Lettuce grows well at 12–17 mol/m²/day. It is a relatively low-light crop, making it ideal for vertical farming and indoor setups with lower-powered LEDs. DLI above 20 may cause tipburn in susceptible varieties.
What is the difference between PPFD and DLI?
PPFD (Photosynthetic Photon Flux Density) measures light intensity at a specific moment in μmol/m²/s — like a speedometer. DLI measures the total light energy accumulated over a full day — like an odometer. DLI = PPFD × photoperiod hours × 3600 / 1,000,000.
Can I increase DLI by extending the photoperiod instead of adding more light?
Yes, for most crops. A longer photoperiod with lower PPFD can achieve the same DLI as a shorter photoperiod with higher PPFD. However, some crops (like cannabis) are photoperiod-sensitive and will trigger flowering at 12 hours regardless of intensity. For tomatoes and lettuce, extending the photoperiod from 16 to 18 hours at the same PPFD increases DLI by 12.5%.