Grow Light PPFD & DLI Calculator
Enter your light's PPFD at the canopy and your photoperiod to get the Daily Light Integral. See if it meets the target for your plant type and how many hours per day you need. Nothing uploaded.
Light Settings
Daily Light Integral
Learn more: PPFD, DLI and why lux does not work for grow lights
How DLI is calculated
Hort Americas gives the formula as DLI = PPFD x photoperiod x 3,600 / 1,000,000. PPFD is the photon flux in the 400 to 700 nm range that plants use for photosynthesis, in micromoles per square meter per second. DLI is the total over a day, in moles per square meter per day.
The calculator uses the same formula. A light delivering 400 PPFD for 12 hours gives 400 x 12 x 3,600 / 1,000,000 = 17.28 mol/m2/day. To hit a target DLI it can also work out the hours: 17.28 / (400 x 3,600 / 1,000,000) = 12 hours.
Target ranges by crop
The same Hort Americas article, quoting Cornell controlled environment agriculture research, lists lettuce at 12 minimum and 17 optimum, strawberry 17 and 20, cucumber 15 to 30, and tomato 20 to 30. It also says continuous DLI above 17 can trigger tipburn in lettuce, and that fruiting crops need 4 to 6 hours of darkness a day.
The calculator's ranges are lettuce 12 to 17, tomatoes 20 to 30, cucumber 15 to 30, strawberry 17 to 25 and seedlings 6 to 12, with a verdict of deficient, optimal or excessive. The same light can be too much for one crop and too little for another.
Why lux is the wrong unit
Lux and lumens measure brightness as the human eye sees it. PPFD counts the photons in the 400 to 700 nm band that drive photosynthesis. Two lights with the same lumen rating can have different spectra and so deliver different PPFD to a plant, which is why grow light specifications use PPFD and DLI.
The calculator's watt-to-PPFD estimate multiplies watts by an efficacy of 2.5 micromoles per joule and divides by the area covered, so a 100 W light over 1 square meter is about 250 PPFD. It ignores how the light spreads, so measure with a PAR meter when you can.
FAQ
What is the difference between PPFD and DLI?
PPFD is the light intensity at one moment. DLI is the total light delivered over a day, which depends on both the intensity and how many hours the light runs.
Can I add hours instead of intensity to reach a DLI target?
Yes, within limits. A dimmer light run for longer can match a brighter one run for less time. Fruiting crops still need a period of darkness, which the Hort Americas article puts at 4 to 6 hours a day.
Why not compare grow lights by lumens?
Lumens describe brightness to the human eye, not the photons plants use. Two lights with the same lumen rating can deliver different PPFD, so compare PPFD at the height and area you will use.