Enter your setup
Example data table
| Scenario | Area | Type | Watts | Efficiency | Target PPFD | Height | Recommended fixtures |
|---|---|---|---|---|---|---|---|
| Seedlings shelf | 0.9 m × 0.45 m | Fluorescent | 54 | 1.2 | 150 | 0.30 m | 1 |
| Herb tent | 1.2 m × 1.2 m | LED | 200 | 2.4 | 300 | 0.45 m | 1–2 |
| Leafy greens rack | 1.5 m × 0.75 m | LED | 150 | 2.6 | 250 | 0.35 m | 1–2 |
| Fruiting plants | 1.2 m × 1.2 m | LED | 320 | 2.8 | 600 | 0.50 m | 1–2 |
| Wide bench | 2.4 m × 1.2 m | HPS | 600 | 1.7 | 500 | 0.60 m | 2–3 |
These examples illustrate typical ranges. Always confirm with a light meter for precision.
Formula used
1) Photon output: PPF ~= watts × efficiency. This estimates total photosynthetic photons per second.
2) Coverage from intensity: area ~= (PPF × UF) ÷ target PPFD. UF is a utilization factor that accounts for optics, height, and reflective surfaces.
3) Footprint limit: footprint ~= pi × (tan(beam/2) × height)^2. If footprint is smaller, it caps usable coverage.
4) Overlap: effective area = min(coverage, footprint) × (1 − overlap%). This improves uniformity near edges.
How to use this calculator
- Measure your grow space length and width using inside dimensions.
- Enter fixture watts and efficiency from the manufacturer specs.
- Pick a target PPFD that matches your crop and growth stage.
- Set mounting height and beam angle for your optic style.
- Estimate reflectivity based on wall material and cleanliness.
- Click Calculate, then export CSV or PDF for your notes.
Practical guidance for coverage planning
Coverage planning for indoor crops
Accurate coverage begins with the grow area footprint and the crop stage. Seedlings and clones usually thrive at lower PPFD targets, while leafy greens and herbs sit mid range. Fruiting plants demand higher intensity and tighter uniformity, so overlap becomes more important. Use this calculator to translate your target intensity into a practical fixture count for tents, benches, and racks. Recording results to CSV or PDF helps keep consistent settings across repeat cycles and seasons.
Understanding efficiency and photon output
Fixture watts alone do not describe plant usable light. The efficiency input converts electrical power into photon output, expressed as PPF. Two fixtures with identical wattage can produce very different PPF values. Enter the manufacturer efficiency when available, or use the built in typical values to estimate performance for planning and budgeting decisions.
Height, beam angle, and footprint limits
Mounting height changes how photons spread across the canopy. As height increases, the same PPF covers more space but the average PPFD drops. Beam angle influences the geometric footprint; narrow optics can cap coverage even if PPF is high. The tool reports whether your setup is PPFD limited or footprint limited, helping you decide between raising, lowering, or changing optics.
Reflectivity and utilization factor
Walls and side curtains recycle a portion of light that would otherwise be lost. Higher reflectivity improves the utilization factor, increasing effective coverage at the same target PPFD. Keep reflective surfaces clean and consider sidewalls for open benches. The calculator applies a reflectivity adjustment to the utilization factor so you can compare a tent, a white room, and an open rack fairly.
Uniformity, overlap, and layout guidance
Edge falloff is common, so professional layouts reserve overlap between fixtures. The overlap setting reduces coverage per fixture to improve uniformity. The suggested grid spacing provides a starting layout for even intensity. After installation, verify with a meter and fine tune by dimming, raising height, or adjusting fixture positions for your crop and canopy density.
FAQs
1) What PPFD target should I choose?
Use 100–200 for seedlings, 200–400 for leafy greens and herbs, and 500–800 for fruiting crops. Start conservative, then verify with a meter and adjust by dimming, height, or fixture count.
2) Why does reflectivity change the result?
Reflective walls return stray photons back to the canopy, improving utilization. A tent or white room often needs fewer fixtures than an open bench for the same target intensity and uniformity.
3) My calculated PPFD is too high. What should I do?
Reduce fixture count, raise mounting height, widen spacing, or dim if your driver supports it. Higher intensity can stress plants and increase water demand, so match the stage and environment.
4) What if the tool says footprint-limited?
Your beam angle at the chosen height caps the lit area. Increase height, use wider optics, or add fixtures for uniform coverage. Narrow optics work best for smaller targets or focused zones.
5) Should I enter manufacturer watts or wall draw?
Use actual wall draw whenever possible because it reflects real electrical input. Nameplate or marketing watts can overstate power, leading to overly optimistic coverage estimates and mismatched intensity.
6) How accurate is this calculator?
It provides planning-grade estimates using efficiency, utilization, and geometry. Real results depend on optics, canopy shape, and environment. Confirm with a PAR meter and refine spacing, height, and dimming for your grow.