Grow Light Planner

Size fixtures for your canopy and check PPFD and DLI against stage targets. Spectrum inputs add red:far-red, blue fraction and crop-steering guidance.

Enter your plants, your light and its height above them to get the hours of light per day they need.

For greenhouses, the DLI Map shows the average sunlight DLI at any location by month, and the grow light needed to reach the target.

About this tool: PPFD, DLI, and choosing a light

🦬 BizonTip!

Use the PPF from the fixture's spec sheet (µmol/s) or its actual power draw, not "equivalent" watts. Verify with a quantum meter at canopy height in several spots. Edges often read well below the center, sometimes half. Growth follows DLI, the daily total, more than PPFD at any one moment. If a light can't reach the target intensity, a longer photoperiod can make up the DLI, except for photoperiod-sensitive plants. Re-measure as plants grow toward the light.

Coverage & PhotoperiodPlants

Target type

Target stagePlant type

Area length ft, growing area under the light

Area width ft

Growing environment

Photoperiod hours of light per day

Custom DLI target optional, mol/m²/d, replaces the stage range

Sunlight DLI mol/m²/d of daylight at the canopy, for a greenhouse. The lights are graded on the rest of the target

Primary FixturesGrow Light

Number of fixturesNumber of lights

Fixture

Fixture outputRated in

Light type determines efficacy estimations. If the box lists PPF, pick PPF above instead.

PPF per fixture µmol/s, from the spec sheet. To enter watts, switch to Watts × efficacy above.

Height above plants in, from the light to the top of the plants

Light spectrum

From the spec sheet. Doesn't need to add to 100.

Trace a picture of the spec sheet's spectrum chart, or shape the curve by hand. Fills the % fields below.

Blue % · 400–500 nm

Green % · 500–600 nm

Red % · 600–700 nm

Far-red % · 700–750 nm

UV % · 280–400 nm

From a spectrum file

Paste two columns, wavelength (nm) and value, from a spectrometer export or a fixture's spectrum data. Fills the bands above and gives a measured red : far-red (655–665 nm over 725–735 nm).

Values are

Light map

Distance to canopy ft from fixture face to canopy top

Space

Border

Auto

ft left out of the stats along each edge. Auto sets it from the room size

Fixture spacing

ft between centers, updates as you type. Leave blank to spread them evenly

Add a fixture

Optimizer

Fixture

Watts each

Second fixture

Watts each

Power limit

Hang height

Max fixtures

Aim for

Benches

Fixtures

Areas/Benches

Worked out from the fixture specs and room reflectance. Real corners usually read a little higher. Uniformity is the lowest dot over the average, inside the border. Sources

Shortcuts

Drag on an empty spot to select several things. Shift-click adds to the selection.
Right-click a fixture or the map for more.
Ctrl/⌘ + C, X, V: copy, cut, paste. D: duplicate. A: select all.
Ctrl/⌘ + Z: undo. Add Shift to redo.
Arrow keys nudge the selection. Hold Shift for bigger steps. R rotates. Delete removes.
Z draws zones, B draws benches, V or Esc goes back to selecting.
Zones and benches select, move, copy and delete like fixtures, alone or mixed with them. Drag a corner to resize one.

Results

Average PPFD assumes even coverage and no losses, so it reads high. Real canopy PPFD drops toward the edges.

Crop steering

Crop

Light goal

Schedule

Crop length days under this light

Finish final days before harvest

UV-C Dose

For germicidal UV-C lamps. Dose is the meter reading at the leaves times the time on.

Meter reading

Unit

Time on seconds per pass

Safety: UV-C and UV-B burn eyes and skin. Never look at a bare lamp. Run it with the room empty, or wear a UV-rated face shield and gloves and cover all skin.

Guidance based on photobiology (phytochrome, cryptochrome, UV photoreceptors), rated by strength of evidence.

Saves this setup to the site picked at the top of the page. To reuse it at other sites, save it as a recipe below.

Lighting Recipes

New Recipe

Recipe name

A recipe saves the full setup: environment, photoperiod, targets, fixtures, spectrum and light map layout. Load it on any site to restore it.

Load a recipe

No saved recipes yet.

Glossary

PPFD (µmol/m²/s): Photosynthetic photon flux density: photons in the photosynthetically active range (PAR, 400–700 nm) reaching one square meter of canopy per second. Shown as "Canopy PPFD". Windowsill houseplants: about 25–150. An LED grow light near the canopy: several hundred.
DLI (mol/m²/d): Daily light integral: total PAR photons reaching one square meter of canopy per day. DLI = PPFD × photoperiod (h) × 0.0036. Shown as "Daily light". Growth tracks DLI more closely than instantaneous PPFD, so a lower PPFD over a longer photoperiod can deliver the same DLI.
Target DLI (mol/m²/d): The DLI range for the selected plants and stage. Shown as "Target". Below it: stretching (etiolation) and slow growth. Well above it: photobleaching and leaf scorch.
Photoperiod (h): Hours of light per 24 hours. Shown as "Hours a day". Simple keeps it between 8 and 16 hours, since most plants need a dark period.
Input power (W): Actual electrical draw at the wall, from the label or spec sheet. Shown as "Watts". "Equivalent" watts (like "100 W equivalent") compare brightness to an incandescent bulb. They are not power and give a wrong result here.
Photon efficacy (µmol/J): Photosynthetic photon efficacy: PAR photons out per joule of electricity in. PPF (µmol/s) = input power × efficacy. Shown as "Light type". Simple estimates 1.5 for a bulb or clip-on light, 2.2 for a budget panel or bar, and 2.7 for a commercial-quality grow light.
Mounting height: Distance from the fixture face to the top of the canopy. Shown as "Height above plants". PPFD drops as height increases because the beam spreads over more area. Re-measure as the canopy grows.
Lit area (ft² or m²): Canopy area the fixture covers. Shown as "Area". Average PPFD is roughly the PPF reaching the canopy divided by the area, so doubling the area about halves it.

About this tool: PPFD, DLI, and choosing a light

Lux vs PPFD

Lux meters measure what the human eye sees. Photosynthesis uses photons from 400 to 700 nm, measured as PPFD. No direct conversion exists between the two.

DLI

DLI is PPFD summed over a day (photons per square meter per day). PPFD is a rate (photons per square meter per second). Plants respond to the daily total.

DLI = PPFD × hours × 0.0036

Sunlight adds to the DLI in a greenhouse or by a window. The DLI Map gives the monthly average from the sun for any location.

Crop and stage	Target DLI
Seedlings and cuttings	6 to 12
Tomato, pepper and eggplant transplants	15 to 20
Lettuce and leafy greens	12 to 17
Basil	12 to 17
Other herbs	8 to 12
Tomatoes, peppers, cucumbers	25 to 30
Cannabis vegetative	30 to 45
Cannabis flowering	30 to 45

Seedlings and transplants: Purdue. Lettuce: Cornell. Fruiting crops: Michigan State. Cannabis vegetative: NC State and UConn trials. Basil, other herbs and cannabis flowering: Bizon estimates (sources).

Measuring PPFD

Measure at canopy height in the center and at each corner. Edges read lower than the center.

Light saturation

Above the saturation point, more light no longer increases photosynthesis and can cause bleaching and leaf scorch.

Spectrum

Blue keeps plants compact, red is the most efficient per watt, far-red makes stems stretch, and green reaches deepest into the canopy. The total amount of light matters more than its color.

Far-red

PPFD and DLI here are 400 to 700 nm, the range every target uses. Far-red (700 to 750 nm) also drives photosynthesis when combined with shorter wavelengths, so when your light has far-red, Advanced also shows ePPFD and eDLI (400 to 750 nm). They are a proposed extension, not a standard, and are not graded. A far-red bar adds to ePPFD, not PPFD (sources).

Fixture efficacy

Compare µmol/J, not watts. Most LED fixtures run about 2.3 to 3. The number depends on the diodes, the driver, the optics and the spectrum, and a whiter, bluer light gives fewer µmol per joule than a red-heavy one. Use the spec sheet for your fixture (sources).

Grow Light Planner