Grow light planning

Grow Light Calculator: PPFD & DLI

Turn your light’s wattage and grow area into the numbers that actually matter — PPFD at the canopy and daily light integral (DLI) — and see exactly how many hours you should run your light for your crop.

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Calculate Your Light

Enter your setup below for an instant PPFD and DLI estimate.

1What are you growing?

2Light type

3Fixture wattage

4Photoperiod

Photoperiod = hours the light runs per day.

5Grow area

Area unit

Canopy coverage

Your Light Levels

Fill in the form and click Calculate PPFD & DLI to see your results here.

0 mol/m²/day

Average canopy PPFD0

Fixture output (PPF)0

Assumes the fixture is hung so its footprint matches your grow area with fairly even spread. Corners and edges receive less PPFD than the center, so treat these as canopy averages.

How the Grow Light Calculator Works

Three steps turn wattage into the two numbers growers actually plan around: PPFD and DLI.

1. Watts become light (PPF)

Wattage × the fixture’s efficiency in µmol/J gives the total photons the lamp emits each second — its PPF.

2. Spread it over your area (PPFD)

PPF divided by grow area in square meters — adjusted for reflector losses — gives the average photons landing on the canopy.

3. Multiply by time (DLI)

PPFD × photoperiod hours × 0.0036 = daily light integral, the total light your plants get in one day.

DLI Targets & Fixture Efficiency Reference

Recommended daily light integral by crop, plus the efficiency ranges you can expect from common light types.

Target DLI (mol/m²/day) by crop. Seedlings and clones want roughly half the lower end of the range.
Crop	Target DLI
Microgreens & seedlings	10–15
Leafy greens (lettuce, kale)	15–20
Culinary herbs (basil, mint)	15–25
Strawberries	20–30
Bell peppers	25–35
Tomatoes	25–40
Cucumbers	25–40
Cannabis (vegetative)	25–40
Cannabis (flowering)	40–65

Typical photosynthetic photon efficacy (PPE) — how many µmol of light each joule of electricity produces.
Light type	µmol/J
LED (high-end)	2.7–3.1
LED (typical)	2.2–2.6
LED (budget)	1.8–2.1
CMH	1.4–1.6
HPS	1.2–1.5
Fluorescent T5	0.7–0.9

Frequently Asked Questions

What is DLI in hydroponics?

DLI (daily light integral) is the total amount of photosynthetically active light a plant receives in one day, measured in mol/m²/day. It is the best single number for planning light schedules because it combines intensity (PPFD) with duration.

What is the difference between PPF and PPFD?

PPF is the total light output of a fixture (micro-moles per second), and PPFD is the light landing on a specific point of the canopy (micro-moles per square meter per second). PPF is a property of the lamp; PPFD depends on your area and hanging height.

How do I convert PPFD to DLI?

Multiply PPFD by the number of hours the light runs, then by 0.0036. Example: 350 µmol/m²/s for 16 hours = 350 × 16 × 0.0036 = 20.2 mol/m²/day.

What PPFD do my plants need?

Leafy greens and herbs thrive around 200–300 µmol/m²/s, fruiting crops like tomato and pepper prefer 400–600, and high-light cannabis flowering can use 700–1100. Use DLI rather than PPFD alone, since duration matters just as much.

How many hours should I run my grow light?

Whatever schedule delivers the crop’s target DLI. For leafy greens you typically need 14–18 hours at 200–300 PPFD; for flowering high-light crops you may need 12–18 hours at higher PPFD. The calculator above works it out from your fixture and area.

Are LED grow lights more efficient than HPS?

Yes. Modern full-spectrum LEDs convert electricity to light at roughly double the efficiency of HPS (2.2–3.1 vs 1.2–1.5 µmol/J), which means more light and less heat per watt.

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Disclaimer: These are planning estimates based on typical fixture efficiencies. Actual PPFD depends on hanging height, spectrum, and reflector design. © MistCulture.com