Daily Light Integral Calculator

How to use this calculator

1. Enter the average PPFD measured at the plant canopy.
2. Enter the number of hours the measured lighting level applies each day.
3. Read the daily photon total and compare it with guidance specific to your crop and growth stage.

Formula and method

For the assumptions behind these results, read the explanation below. You can also explore CO₂ Grow Room and Plant Spacing.

Intensity and duration describe different things

PPFD is the number of photosynthetically active photons arriving at a square meter each second. DLI adds those arrivals over an entire day. This makes it possible to distinguish a brief period of strong light from many hours of moderate light. Identical daily totals can be produced by different combinations of intensity and duration.

The conversion has two steps. Multiply hours by 3,600 to obtain seconds, then multiply by PPFD to obtain micromoles per square meter. Dividing by one million converts micromoles to moles. The area remains in the denominator, so this result is a daily exposure per unit area rather than the lamp’s total photon output.

Using a representative measurement

Measure near the leaves rather than next to the lamp. A single bright spot may overstate what the entire crop receives. Multiple measurements across the canopy, averaged appropriately, provide a better basis for comparing growing areas. This calculator assumes the entered average remains applicable throughout the stated lighting period.

Sunlight changes through the day. For variable conditions, divide the day into intervals, calculate each interval using its average PPFD, and sum the totals. A logging quantum sensor can perform that integration directly. DLI alone does not describe spectrum, day-length response, heat stress, or light saturation, so an equal DLI does not guarantee an equal biological response.