Calculate Daily Light Integral (DLI) from your grow light’s PPFD and photoperiod, or find what PPFD and hours you need to hit a target DLI for any crop.
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Daily light integral is the total amount of usable light a plant receives in a day. It is calculated by multiplying the PPFD in micromoles per square meter per second by the hours of light and by 3,600 seconds per hour, then dividing by a million to give moles per square meter per day. A PPFD of 200 for 16 hours gives about 11.5.
Each crop has a target range. Leafy greens and herbs often do well at roughly 12 to 17 moles per day, while fruiting crops such as tomatoes and peppers need about 20 to 30 or more. If your light gives less than the target, you can raise the PPFD by moving the light closer or adding fixtures, or increase the photoperiod, as long as the plant tolerates it.
The calculator also works backward, finding the hours you need for a given PPFD to reach a target. Measure the PPFD at the top of the canopy and across the growing area, since the light is rarely even. Where sunlight adds to the artificial light, add the sun’s contribution, which varies with the season and the weather.