- Pick Area average for tents, beds, and shelves.
- Enter fixtures, wattage, and either µmol/J or lm/W.
- Set area dimensions and photoperiod to compute DLI.
- Adjust CU and LLF for reflectivity and aging.
- Use uniformity to compare hotspot vs even coverage.
- Click Calculate, then export CSV or PDF if needed.
| Setup | Inputs (summary) | Estimated outputs |
|---|---|---|
| 1× LED panel | 1 fixture, 150 W, 2.6 µmol/J, 1.2×1.2 m, CU 0.75, LLF 0.9, 18 h | PPFD ≈ 190, DLI ≈ 12.3, Lux ≈ 13,300 |
| 2× bars | 2 fixtures, 120 W each, 130 lm/W, 1.0×1.0 m, CU 0.8, LLF 0.9, 16 h | PPFD ≈ 214, DLI ≈ 12.3, Lux ≈ 15,000 |
| Flower push | 1 fixture, 300 W, 2.8 µmol/J, 1.2×1.2 m, CU 0.8, LLF 0.9, 12 h | PPFD ≈ 420, DLI ≈ 18.1, Lux ≈ 29,400 |
Converting Fixture Specs to Canopy Intensity
This calculator starts with fixture count and real watt draw, then translates efficiency into useful plant light. If your label provides µmol/J, total PPF equals watts multiplied by efficacy. Average PPFD is then PPF adjusted by CU and LLF, divided by canopy area. In lm/W mode, it estimates lumens first, converts to lux, and uses a spectrum factor to approximate PPFD. Use measured values for planning.
Choosing Target PPFD and DLI by Crop Stage
Light targets should be set by growth stage, not by wattage alone. Many seedlings thrive near 100–250 µmol/m²/s, while leafy greens often perform around 200–400. Fruiting crops and dense flowering can require 600–900, depending on temperature and CO₂. DLI ties intensity to time: 12–17 mol/m²/day often suits many greens, 17–30 is common for heavy production. Adjust photoperiod first before buying hardware.
Why CU and LLF Change Real-World Results
CU and LLF are practical correction factors that explain why identical lights deliver different results in real gardens. White walls, reflective trays, and tight enclosures can raise CU toward 0.85–0.95, while open benches may sit near 0.55–0.75. LLF captures lens dirt, diode aging, and driver losses; values of 0.85–0.95 are typical. Use conservative factors when comparing vendors.
Uniformity, Mounting Height, and Hotspot Control
Uniformity matters because plants respond to the weakest part of the canopy. A uniformity ratio of 0.50 means edges receive about half the hotspot intensity, which can slow growth and create uneven moisture demand. Raising the fixture and using wider optics usually improves evenness but lowers peak PPFD. For multi-fixture layouts, overlap and reflective surfaces smooth the map. Verify by measuring a simple grid.
Energy Planning and Cost per Mol of Light
Energy planning is straightforward once PPFD and photoperiod are set. Daily kWh equals total watts divided by 1000, multiplied by hours. To compare systems, estimate photons per day: PPF times photoperiod seconds, then convert to moles. Higher µmol/J reduces cost per mol and heat load, which can improve humidity control. Use this report to document upgrades, and track results after each change for your specific crop.
1) What is the difference between PPFD and DLI?
PPFD is light intensity at a moment, measured in µmol/m²/s. DLI is the total light delivered in a day, measured in mol/m²/day. DLI depends on both PPFD and photoperiod.
2) Should I use µmol/J or lm/W?
Use µmol/J whenever the manufacturer provides it, because it is already tied to plant-usable photons. Use lm/W only when PAR specs are missing, and treat the PPFD conversion as an approximation.
3) How do I choose the spectrum conversion factor k?
k varies with spectrum and sensor response. For many white LEDs, 65–75 lux per µmol/m²/s is a common planning range. If you have meter data for your light, enter a custom k for better estimates.
4) Why does my measured PPFD differ from the estimate?
Real canopies include reflections, driver variation, dimming, heat, and canopy shape. Hanging height and mapping method also change results. Use CU and LLF conservatively, then refine inputs using a few PAR meter readings.
5) What CU and LLF values should I start with?
For reflective tents, start CU 0.75–0.90. For open shelves, start 0.60–0.75. Use LLF 0.90 for clean, newer lights, and 0.85 when lenses are dusty or the fixture is older.
6) Can this calculator replace a PAR meter?
No. It helps plan layouts, compare options, and document assumptions. A PAR meter is still the best way to confirm hotspots, edges, and real PPFD at canopy level before finalizing crop targets.