Calculator
Formula used
Illuminance in lux equals lumens per square meter. This calculator applies practical adjustment factors:
- Effective lumens = Total lumens × UF × MF × (1 − Beam loss) × (1 − Obstruction loss) × Reflectance
- Lux = Effective lumens ÷ Area (m²)
- Foot-candles = Lux ÷ 10.764
How to use this calculator
- Choose a lumen input method and enter your lumen values.
- Enter area directly, or switch to length and width.
- Adjust factors to match your room and fixture behavior.
- Select a plant profile to compare against a target range.
- Press Calculate to see results above this form.
Example data table
| Scenario | Total lumens (lm) | Area (m²) | UF | MF | Losses | Estimated lux |
|---|---|---|---|---|---|---|
| Seedling shelf | 2400 | 0.80 | 0.85 | 0.90 | 10% + 5% | ~2327 |
| Herb counter | 3200 | 1.00 | 0.88 | 0.92 | 8% + 3% | ~2508 |
| Leafy greens rack | 6000 | 1.20 | 0.90 | 0.92 | 12% + 6% | ~3432 |
| Fruiting tent | 16000 | 1.50 | 0.92 | 0.90 | 10% + 5% | ~7442 |
Tip: If lux looks low, reduce area, raise lumens, or improve reflectance.
Light intensity basics for indoor gardening
Indoor horticulture benefits from measuring illuminance because it links lamp output to the plant canopy. Lux equals lumens per square meter, so it is a practical bridge between product specs and real growing areas. When you record lux at the leaf surface, you can compare zones, detect dim corners, and standardize shelves or tents across seasons. Consistent records help you spot driver failures and schedule replacement before yield drops.
Translating fixture lumens into canopy lux
Start with total lumens from a lamp label or by multiplying fixtures by lumens each. Next, define the lit footprint in square meters. If your space is measured in feet or inches, convert before dividing. For irregular beds, estimate area by averaging widths along the length, then confirm with a quick tape measure check. The calculator then reports lux and foot‑candles, letting you communicate targets with suppliers and reference charts.
Adjusting for distance, losses, and reflectance
Real installations rarely deliver all rated lumens to leaves. Utilization factor reflects beam spread, mounting height, and how much light actually lands within the footprint. Maintenance factor accounts for dust, aging, and lens haze. Beam and obstruction losses represent spill and shading from rails, pots, or plant structure. A reflectance factor rewards white walls and reflective liners. Review factors after any layout change, because small shifts can move the canopy into a different intensity band.
Matching lux ranges to plant stages
Plant needs change with growth stage and species. Seedlings tolerate lower intensity, while leafy greens generally prefer stronger, even coverage to avoid stretching. Fruiting and flowering crops usually require the highest intensity and longer photoperiods. Use the plant profile check as a starting point, then validate with growth response, leaf color, and temperature management.
Using results for layout and energy planning
After calculating, refine the layout. If lux is low, reduce the footprint, add fixtures, or lower mounting height while maintaining uniformity. If lux is high, raise fixtures or dim to reduce waste heat and power draw. Aim for steady readings across the canopy, not just a bright center. Save CSV results for logbooks, and generate PDFs for clients, audits, or greenhouse commissioning.
FAQs
1) What does lux mean in this calculator?
Lux is illuminance at the growing surface. It equals the effective lumens reaching the area, divided by square meters, helping you compare lighting levels across shelves, beds, or tents.
2) Why are utilization and maintenance factors included?
They estimate real delivered light. Utilization captures beam spread and coverage, while maintenance accounts for aging, dust, and optics losses. Together they reduce unrealistic results from label lumens.
3) Which area should I enter for a shelf or bed?
Use the footprint you want evenly lit at canopy height. If light spills beyond edges, include that spill area, or increase beam loss to represent wasted light outside the target zone.
4) Is lux the same as PPFD?
No. Lux is weighted to human vision, while PPFD measures plant‑useful photons. Lux is still useful for consistency checks, but use a PAR meter when you need crop‑specific precision.
5) What reflectance factor should I choose?
Start near 1.0 for neutral rooms. Use 1.05–1.20 for white walls or reflective liners, and closer to 0.90 if surfaces are dark or absorbent.
6) How often should I recheck lighting levels?
Recheck after moving fixtures, changing plant height, cleaning lenses, or altering wall coverings. For stable setups, a monthly spot check helps catch gradual output decline.