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Hydroponics

Grow light

DLI calculator for hydroponic and indoor aquaponic crops. Enter your PPFD reading and photoperiod, see if you're hitting the crop's daily light target.

Grow light DLI from PPFD × hours
Or set a target manually below.
to
Defaults to leafy-greens range. Picking a crop updates these.
Measure with a PAR meter at canopy height. Manufacturer specs are inflated by 20-30%; verify with a meter when you can.
Typical: 14-16 for greens, 12-14 for fruiting crops with a dark recovery period.
DLI achieved -- mol/m²/day
Target range --
Status --
To hit minimum --
DLI is `PPFD × hours × 0.0036`. The target ranges come from each crop's profile data (Cornell CEA, U. Arizona CCAC, and grower references). A 20% margin above the minimum is healthy; aim there rather than the bare minimum.

What this calculates

Daily Light Integral (DLI). The formula is PPFD × hours × 0.0036. PPFD is the instantaneous photon flux at the canopy in μmol/m²/s; multiply by your photoperiod in hours and convert (3600 seconds/hour × 1e-6 = 0.0036) and you get mol/m²/day, which is the standard agronomic measure of how much light a plant got across the whole day.

DLI is what plants actually respond to. A really intense light running 6 hours can deliver the same DLI as a moderate light running 18 hours. Below a crop's minimum DLI you get etiolation (leggy growth, weak fruit set, leaves stretching for light). Above the maximum you waste electricity and risk photo-oxidation.

How to use it

Pick your crop from the list. Each one has a verified DLI range from the underlying database (sources are listed on each crop's profile page). Enter your PPFD reading and how long the light runs per day. The calc shows whether your setup hits the target.

PPFD measurement: a real PAR meter is the only honest way. A phone lux meter app is off by enough that the result is misleading. Apogee, LI-COR, or Photone (if you must use a phone) are the usual options. Position the sensor at the canopy, not at floor level or right under the fixture; you want what the leaves see.

If you don't know your PPFD, manufacturer specs are typically inflated. Subtract 20-30% from the spec to get a realistic at-canopy value, then verify with a meter when you can.

Common DLI targets

For sanity-check reference:

  • Lettuce, leafy greens: 12-17 mol/m²/day. Achievable with a 150W LED at moderate distance for 14-16 hours.
  • Herbs (basil, parsley): 10-15 mol/m²/day. Similar setup to lettuce, basil tolerates more.
  • Tomatoes, peppers: 22-30 mol/m²/day. This is the demanding end. You need real lighting and a long photoperiod, or supplemental on top of sun.
  • Strawberries: 17-22 mol/m²/day. Lighting matters more than most growers think.
  • Microgreens: 10-15 mol/m²/day. Forgiving but a low DLI gives leggy growth.

If you're growing fruiting crops indoors and hitting only 12-15 DLI, your harvest will be small or non-existent. Those crops need 20+ DLI to set fruit at any meaningful rate.

Two ways to get to target

If you're under your crop's DLI minimum, you have two levers:

  • Longer photoperiod. Cheap to extend (just runs longer). Diminishing returns: most fruiting crops need a dark period for respiration, and 18+ hour photoperiods don't help much above a point.
  • More PPFD. More electricity, more heat, and a stronger or closer fixture. The reliable lever for getting from "growing OK" to "growing well".

The calc suggests both. Pick whichever is cheaper or more convenient for your setup.

Further reading