Daily Light Integral (DLI) Calculator
Use this tool to calculate DLI from PPFD and photoperiod, or calculate the PPFD needed to reach a target DLI.
Calculate DLI
Formula: DLI = PPFD × 3600 × hours ÷ 1,000,000
Calculate Required PPFD
Formula: PPFD = (Target DLI × 1,000,000) ÷ (3600 × hours)
What is DLI?
DLI stands for Daily Light Integral. It measures the total amount of photosynthetically active light that plants receive in one day. While PPFD tells you the light intensity at a moment in time, DLI combines intensity + duration so you can evaluate the complete lighting plan.
DLI is expressed as mol/m²/day (moles of photons per square meter per day). This makes it one of the most useful metrics for greenhouse growers, indoor growers, and hobby gardeners using grow lights.
Why DLI matters for plant growth
Plants respond to accumulated light. If intensity is low but lights are on longer, total light can still be enough. If intensity is very high but duration is short, growth may be limited. DLI gives you one clear target to manage: enough daily photons for the crop and stage.
- Too low DLI: slow growth, stretching, weak stems, low yields.
- Right DLI: compact growth, healthy leaves, better biomass and production.
- Too high DLI: wasted energy, possible stress/bleaching if not balanced with CO₂, nutrients, and temperature.
Target DLI ranges by crop type
| Crop Type | Typical DLI Target (mol/m²/day) | Notes |
|---|---|---|
| Seedlings / Propagation | 6–12 | Lower light to avoid stress while establishing roots. |
| Leafy greens (lettuce, spinach) | 12–17 | Good for fast, compact leafy growth indoors. |
| Herbs (basil, cilantro, mint) | 14–20 | Higher end can improve density and aroma in many herbs. |
| Vegetative cannabis / fruiting veggies early stage | 20–30 | Supports stronger structure before flowering/fruiting. |
| Tomato, pepper, cucumber, flowering/fruiting crops | 25–40+ | Higher light demand; environment and nutrition must keep pace. |
How to use this DLI calculator
1) If you know PPFD and hours
Enter your average canopy PPFD and the light-on time in hours. The calculator returns DLI instantly so you can compare against crop targets.
2) If you know your DLI target
Enter target DLI and photoperiod. The calculator returns the required average PPFD, which helps you choose fixture output, dimmer settings, and hanging height.
Example
Suppose your grow space averages 300 µmol/m²/s for 14 hours/day:
DLI = 300 × 3600 × 14 ÷ 1,000,000 = 15.12 mol/m²/day
That DLI is often suitable for many leafy greens, but may be low for high-yield fruiting crops.
If you only have lux measurements
Lux is weighted for human vision, not plant photosynthesis, so it is imperfect for plant lighting. Still, for white LED fixtures, a rough estimate can be used:
PPFD ≈ lux × 0.013 to 0.018(varies by spectrum)- Then use PPFD in this calculator for DLI
Best practice: measure PPFD directly with a quantum sensor if precision is important.
Common mistakes to avoid
- Using fixture-center PPFD instead of canopy-average PPFD.
- Ignoring photoperiod changes between vegetative and flowering stages.
- Chasing very high DLI without adequate CO₂, nutrients, airflow, and irrigation.
- Not accounting for plant height changes that affect light intensity at the canopy.
Final thought
DLI is one of the simplest high-impact metrics in controlled environment agriculture. With a clear DLI target, you can tune your lighting strategy for healthier plants and better efficiency.