Grow light and daily light integral calculator
Work out the PPFD and DLI your crop actually needs, how many fixtures that takes, what it costs to run, and how much heat your cooling has to remove. Everything runs in your browser.
Space and light target
Light required
Fixture and energy
Power, cost and heat
Same light, different technology
What it costs to deliver the identical photon output with each lighting technology. Efficacies are measured figures, all on the 400–700 nm basis.
| Technology | Efficacy (µmol/J) | Input power | Energy / month | Cost / month | Heat (BTU/hr) | vs your fixture |
|---|---|---|---|---|---|---|
| High-efficacy LED | 3.20 | |||||
| Modern LED | 2.80 | |||||
| DLC V4.0 minimum | 2.50 | |||||
| Double-ended HPS 1000 W | 1.70 | |||||
| HPS 400 W, magnetic ballast | 0.94 | |||||
| T5 fluorescent | 0.95 |
Swapping T5 fluorescent for a modern LED at the same photon output cuts lighting energy and lighting heat by roughly two thirds — the single biggest lever on a rack. HPS is shown for completeness but is rarely practical on a vertical tier, because of the standoff distance its radiant heat demands.
How it works
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PPF and PPFD are not the same number
PPFD (µmol/m²/s) = PPF (µmol/s) × coverage ÷ area (m²)
PPF is what the fixture emits in every direction. PPFD is what arrives at a square metre of canopy. Reading a 425 µmol/s fixture spec as "425 PPFD" overstates canopy intensity three- to fourfold, and is why growers under-buy fixtures and then conclude LEDs do not work. Lux and "equivalent wattage" are not usable at all — lux weights light by human vision, which undervalues exactly the red and blue photons plants use most.
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DLI is the number that grows the crop
DLI (mol/m²/day) = PPFD × photoperiod (h) × 0.0036
The constant is just arithmetic: 3,600 seconds per hour divided by a million micromoles per mole. Biomass tracks the daily photon dose, not the instantaneous intensity — which means intensity and hours trade off against each other, and a longer photoperiod at lower intensity can hit the same target with fewer fixtures.
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Not every photon lands on the crop
Some of what a fixture emits spills onto aisles, walls, and the underside of the tier above. Coverage utilisation is that fraction — roughly 0.85 for an enclosed rack tier with reflective sides, lower for an open rack. Leaving it at 1.0 overstates delivered light by 15–30%, always optimistically. Real numbers for a specific fixture come from its photometric map, not from a calculator.
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An average is not a uniform field
PPFD directly under a fixture can be twice the value at a tier corner. The average can be exactly on target while edge plants are light-starved and centre plants are tipburning. Treat the figures here as averages and check the manufacturer’s PPFD map before committing to a layout.
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In a sealed room, all of the power becomes heat
Heat (BTU/hr) = total input watts × 3.412
The efficient fraction does not escape — PAR photons are absorbed by canopy, substrate, and walls and end up as heat, with only one or two percent stored as biomass. Sizing cooling on the fixture’s inefficiency alone under-sizes it by roughly two and a half times, which shows up as a room that cannot hold setpoint at lights-on, after the equipment is bought.
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Mushrooms are not a DLI crop
Fungi are not photosynthetic, so PPFD and DLI do not apply to them at all — a DLI target for mushrooms is a category error. Light in mushroom growing is a morphogenic trigger for pinning and stipe development, at intensities on the order of one or two percent of a lettuce dose. If you are planning a mushroom room, size the light for the signal and use this tool only for any leafy-greens side of the operation.
Lighting is one line in the cost of a crop. Add materials, labor and overhead with the craft farm COGS calculator, or plan a mushroom block operation with the substrate and yield calculator.