How do you convert PPFD to DLI?

Multiply PPFD (µmol/m²/s) by your photoperiod in hours, then by 0.0036. Example: 500 PPFD × 16 h × 0.0036 = 28.8 mol/m²/day. The 0.0036 constant converts per-second micromoles into per-day moles (× 3600 seconds/hour ÷ 1,000,000 µmol/mol).

Does photoperiod change the DLI?

Yes — DLI is intensity multiplied by time. The same PPFD over 18 hours delivers 50% more daily light than over 12 hours. That is why a calculator that only asks for PPFD cannot give you a real DLI: it is missing half the equation.

What is a good DLI for cannabis flower?

Commonly 35–45 mol/m²/day, pushed higher only with supplemental CO₂. Hitting it at a 12-hour flower photoperiod takes roughly 800–1,000+ µmol/m²/s of PPFD at the canopy.

What is a good DLI for leafy greens?

About 12–17 mol/m²/day, achievable around 200–400 µmol/m²/s over a 14–18 hour day. Lettuce and most herbs finish well in that range without the intensity a fruiting or flowering crop needs.

What PPFD do I need for a target DLI?

Required PPFD = target DLI ÷ (photoperiod hours × 0.0036). For a DLI of 30 at an 18-hour day: 30 ÷ (18 × 0.0036) ≈ 463 µmol/m²/s. Switch this calculator to reverse mode to do it for your own numbers.

PPFD to DLI Calculator

Enter your canopy PPFD and photoperiod to get the Daily Light Integral — or work backward from a target DLI to the PPFD you need. Checked against growth-stage targets.

Your Light

Crop / Stage

Cannabis Flower: target DLI 35–45 mol/m²/day · PPFD 800–1000 µmol/m²/s

PPFD (canopy intensity)600 µmol/m²/s

Measured photosynthetic photon flux density at the canopy.

Photoperiod18 h/day

Hours of light per day.

Key Takeaways

DLI = PPFD × photoperiod hours × 0.0036 — intensity multiplied by time.
PPFD is instantaneous intensity (µmol/m²/s); DLI is the total daily dose (mol/m²/day) the plant actually responds to.
Same PPFD, different photoperiod = different DLI — you cannot skip the photoperiod, which is what most "DLI calculators" leave out.
PPFD by stage: seedlings 100–300, veg 200–400, flower/fruiting 600–1,000, high-light 800–1,500 µmol/m²/s.
A single meter reading overstates DLI; a fixed PAR sensor logging continuously gives the real canopy average.

What is DLI, and how is it different from PPFD?

PPFD (photosynthetic photon flux density) is intensity — how many usable photons land on a square metre every second, in µmol/m²/s. It is an instantaneous snapshot. DLI (daily light integral) is dose — the total moles of those photons delivered over a full day, in mol/m²/day. It is intensity multiplied by time. Two rooms can read the same PPFD and deliver completely different DLI: 600 µmol/m²/s for 12 hours is 25.9 mol/m²/day, but the same 600 for 18 hours is 38.9. The plant responds to the daily dose, so PPFD alone cannot tell you whether you are under- or over-lighting.

The PPFD → DLI formula

DLI = PPFD × photoperiod hours × 0.0036. The 3600 converts per-second to per-hour, and dividing by 1,000,000 converts micromoles to moles; combined, the constant is 0.0036. To go the other way — you know your target DLI and photoperiod and want the PPFD to dial in — required PPFD = target DLI ÷ (hours × 0.0036). The calculator above does both directions.

Why a meter reading at one spot isn't your DLI

PPFD varies enormously across a canopy — center-to-edge falloff of 30–50% is normal under a single fixture. A handheld reading at the brightest spot overstates the average DLI the crop actually receives. To trust your number you need either a light map of many readings averaged, or a fixed PAR sensor logging continuously — which also catches driver dimming, photoperiod drift, and fixture aging that a one-time reading never will.

Frequently Asked Questions

How do you convert PPFD to DLI?: Multiply PPFD (µmol/m²/s) by your photoperiod in hours, then by 0.0036. Example: 500 PPFD × 16 h × 0.0036 = 28.8 mol/m²/day. The 0.0036 constant converts per-second micromoles into per-day moles (× 3600 seconds/hour ÷ 1,000,000 µmol/mol).
Does photoperiod change the DLI?: Yes — DLI is intensity multiplied by time. The same PPFD over 18 hours delivers 50% more daily light than over 12 hours. That is why a calculator that only asks for PPFD cannot give you a real DLI: it is missing half the equation.
What is a good DLI for cannabis flower?: Commonly 35–45 mol/m²/day, pushed higher only with supplemental CO₂. Hitting it at a 12-hour flower photoperiod takes roughly 800–1,000+ µmol/m²/s of PPFD at the canopy.
What is a good DLI for leafy greens?: About 12–17 mol/m²/day, achievable around 200–400 µmol/m²/s over a 14–18 hour day. Lettuce and most herbs finish well in that range without the intensity a fruiting or flowering crop needs.
What PPFD do I need for a target DLI?: Required PPFD = target DLI ÷ (photoperiod hours × 0.0036). For a DLI of 30 at an 18-hour day: 30 ÷ (18 × 0.0036) ≈ 463 µmol/m²/s. Switch this calculator to reverse mode to do it for your own numbers.