A little knowledge. A greener home. Explore the plant index ↗
Home / Grow lights

Light / A measured approach

Make sense of
your grow light.

Turn a measured light intensity and lamp schedule into daily light integral. Start with a PAR reading at leaf height.

01

Your light setup

Use an average measured across the plant’s canopy, not the lamp’s wattage. This calculation covers lamp light only; unmeasured daylight is not included.

One day of lamp light

Save this setup ↗

Light × time.

DLI = PPFD × hours × 3,600 ÷ 1,000,000. At 200 µmol/m²/s for 12 hours, a lamp supplies 8.64 mol/m²/day.

The optional target is yours, not a recommended prescription. Required lamp hours = target ÷ (PPFD × 0.0036). More than 24 hours is physically unavailable.

Method: Purdue Extension: Daily Light Integral · checked 4 Oct 2026

What this cannot tell you

Lux, lumens and watts cannot be universally converted into PPFD: the spectrum, fixture, distance and distribution matter. A phone lux meter is not automatically a calibrated PAR sensor.

Plants also need a suitable day/night pattern. Reaching a numeric DLI does not make a 24-hour lighting schedule suitable. Acclimate plants and consult species-specific guidance.

Understand the light in your room ↗