Grow-light DLI calculator

Turn a PPFD reading and the hours your light is on into a daily light integral (DLI), the total light your plant gets in a day.

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No PPFD meter?

PPFD can't be worked out from a bulb's wattage, lumens or the claims on the box, so this calculator needs a real reading.

A quantum (PAR) sensor measures PPFD directly. Hold it level at leaf height and average a few spots under the light.
Lux meters and phone light apps measure light as human eyes see it. They can't reliably give PPFD for grow lights, especially coloured LEDs.
Without a reading, go by the plant's light description (low, medium, bright indirect, some direct sun) and watch how new growth responds.

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How it works

DLI is the amount of photosynthetic light reaching a surface over a day, in moles per square metre per day. It's calculated from PPFD (µmol/m²/s), measured at leaf height, and the hours the light is on: DLI = PPFD × 3,600 × hours ÷ 1,000,000. You can add up to three periods, for example window light plus a grow light.

What it can't do

It needs a real PPFD reading from a quantum (PAR) sensor. PPFD can't be worked out reliably from wattage, lumens or a lux meter, especially under coloured LEDs. It doesn't give targets for specific plants.

How it works

What it can't do

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