Calculator
Example Data Table
| Scenario | Input | Photoperiod | Estimated PPFD | Calculated DLI |
|---|---|---|---|---|
| Leafy greens indoors | PPFD = 250 µmol/m²/s | 16 h/day | 250 µmol/m²/s | 14.40 mol/m²/day |
| Lux reading (white LED) | Lux = 15000, factor 0.015 | 14 h/day | 225 µmol/m²/s | 11.34 mol/m²/day |
| Fixture estimate | PPF = 700 µmol/s × 2, eff 0.85, area 1.2 m² | 12 h/day | ≈ 992 µmol/m²/s | ≈ 42.86 mol/m²/day |
Formula Used
Daily Light Integral (DLI) summarizes how much usable light plants receive in one day.
- PPFD is the light intensity: µmol/m²/s.
- Photoperiod is hours of light each day.
When you only have lux or foot-candles, the calculator estimates PPFD using a factor that depends on spectrum. Use the preset factor, or enter a custom factor from your own measurements.
How to Use This Calculator
- Choose From measurements if you measured PPFD, lux, or foot-candles.
- Enter your photoperiod (hours of light per day).
- If using lux or foot-candles, select a light source preset or enter a custom factor.
- Optionally set a target DLI to see the gap and required supplemental PPFD.
- Press Calculate DLI, then download CSV or PDF reports if needed.
Why DLI matters in gardening
Daily Light Integral (DLI) is the total photosynthetic light a plant receives per day, reported as mol/m²/day. It turns scattered readings into a usable daily budget, which is especially helpful for greenhouses, indoor shelves, and short winter days. Two setups can look equally bright at noon yet deliver very different daily doses. Tracking DLI also makes seasonal changes easy to compare. for repeatable crop planning.
Interpreting PPFD and photoperiod
PPFD describes light intensity at canopy height in µmol/m²/s. Converting intensity to DLI is a time step: multiply PPFD by 3,600 seconds and by lighting hours, then divide by 1,000,000. Example: 250 µmol/m²/s for 16 hours gives about 14.4 mol/m²/day. If photoperiod drops from 16 to 12 hours with the same PPFD, DLI falls 25%, often slowing leaf expansion.
Using lux and foot-candles responsibly
Lux and foot‑candles are human‑weighted brightness units, so a spectrum factor is needed to estimate PPFD. A typical white LED estimate is about 0.015 µmol/m²/s per lux, meaning 15,000 lux approximates 225 µmol/m²/s. HPS, sunlight, and “blurple” fixtures can shift the factor. Use these conversions for planning, then verify with PAR/PPFD measurements when precision matters.
Setting targets for common crops
Targets keep lighting decisions practical. Many seedlings perform around 4–8 mol/m²/day, leafy greens often sit near 10–17, and fruiting crops may benefit from 20–30+ when temperature, CO₂, and nutrition are controlled. A target is a planning tool, not a promise. The calculator converts any DLI gap into supplemental PPFD for your chosen photoperiod, helping you decide whether to raise intensity or extend hours.
Fixture planning and efficiency
When only fixture specs are available, use PPF (µmol/s) to estimate average PPFD by dividing usable photons by area. Real rooms lose light to distance, optics, reflections, and uneven coverage, so an efficiency factor around 0.70–0.90 is common. After installation, take several canopy readings, average them for DLI, and review the spread to find hot and dim zones.
FAQs
What DLI range suits leafy greens?
Many leafy greens do well around 10–17 mol/m²/day. Start near the lower end for cool, compact growth, then adjust based on temperature, cultivar, and spacing. Monitor leaf size, color, and stretch to fine‑tune.
How should I measure PPFD at the canopy?
Measure at plant height with a PAR/PPFD meter. Take multiple points across the growing area, avoid shadows from your body, and average the readings. Recheck after raising plants or changing dimmer settings.
Can I rely on a lux meter instead?
A lux meter can guide setup, but it needs a spectrum factor to estimate PPFD. White LEDs are often near 0.015 µmol/m²/s per lux, yet fixtures vary. Use it for trends, then confirm with PPFD when accuracy matters.
Why might fixture-based DLI differ from measured DLI?
Fixture specs assume ideal conditions. Real spaces lose photons due to distance, beam angle, reflections, and uneven coverage. The utilization efficiency accounts for those losses, but measurements at the canopy are the most reliable check.
Is it better to increase hours or intensity?
Both raise DLI. Longer hours can be gentler on heat and power draw per moment, while higher PPFD can improve compactness but may stress plants. Stay within a sensible photoperiod and adjust PPFD to meet your target.
What does utilization efficiency mean here?
It is the fraction of fixture photons that reach your canopy area. Values often land between 0.70 and 0.90 depending on height, reflectivity, and layout. If you are unsure, use a conservative value and verify with measurements.