DLI Calculator (Daily Light Integral)
Calculate the Daily Light Integral (DLI) from your PPFD reading and photoperiod. Enter the light level in umol/m2/s and hours of light per day to get DLI in mol/m2/day with a quick band note.
How to calculate DLI
- Enter your PPFD reading in umol per square meter per second.
- Enter the photoperiod, the hours of light per day.
- Read the DLI in mol per square meter per day and its band note.
Examples
PPFD 400 for 16 hours
400 umol/m2/s, 16 h/day
23.04 mol/m2/day (moderate light)
Frequently asked questions
How is DLI calculated?
DLI equals PPFD times the photoperiod in seconds, divided by one million. In formula form: DLI = PPFD x hours x 3600 / 1,000,000, giving mol per square meter per day.
What is a good DLI for my plants?
As a general guide, below about 12 suits leafy greens and low light houseplants, 12 to 30 covers most fruiting and flowering crops, and above 30 favors sun loving crops. Targets vary by species, so treat these as guidelines.
Where do I get a PPFD value?
Measure PPFD with a quantum or PAR meter at canopy height, or use the manufacturer PPFD map for your fixture at your hanging height. Average several points for a fuller picture.
Does DLI account for light moving across the canopy?
It uses a single average PPFD over the photoperiod. Real canopies see uneven light, so sample several spots and average them for a more representative DLI.
Why cap the photoperiod at 24 hours?
A day only has 24 hours of possible light, so values above 24 are rejected. Many crops also need a dark period, so longer is not always better even when allowed.
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