Grow Light Cost & PPFD Estimator

Grow Light Cost and PPFD Fundamentals

Indoor growing relies on light intensity and duration. PPFD (photosynthetic photon flux density) measures how many photosynthetically active photons reach the canopy each second. However, plants respond to total daily light, not just instantaneous intensity. That total is the Daily Light Integral (DLI), reported in mol/m²/day. DLI accounts for both PPFD and the number of hours the light runs, making it the most useful metric for comparing lighting schedules in hydroponics, vertical farming, or greenhouse supplementation.

Electrical cost is driven by power draw and runtime. A 250 W fixture running 16 hours per day uses 4.0 kWh daily (0.25 kW × 16 h). Multiply by your electricity rate to estimate daily cost and scale to monthly or yearly totals. Real-world bills can vary due to time-of-use pricing, HVAC loads, and fan power, but this calculator gives a reliable baseline for energy planning and ROI analysis in controlled-environment agriculture.

Use the DLI output to match crop requirements. Leafy greens often thrive around 12–17 mol/m²/day, while fruiting crops may need 20–30+ mol/m²/day. If your DLI is too low, increase PPFD or hours; if it is too high, reduce intensity or photoperiod to avoid photoinhibition or excess heat. Pair this lighting strategy with irrigation duty cycles and nutrient planning to optimize yield and energy efficiency for homesteading or commercial systems.

PPFD readings can vary across the canopy, especially with uneven fixture spacing. For accurate planning, measure PPFD at multiple points and use the average. Dimming a fixture reduces both PPFD and power draw, which can lower costs without changing photoperiod. Some growers prefer longer photoperiods at lower intensity to manage heat and improve uniformity. Use this tool to compare those scenarios: the DLI stays similar while cost and heat loads shift. That flexibility is valuable for indoor farms balancing crop quality with energy budgets.

Formula

Daily energy use is \(E = (W/1000) \times h\). Electricity cost is \(E \times c\), where \(c\) is the price per kWh. DLI is computed as: \(\text{DLI} = \frac{\text{PPFD} \times 3600 \times h}{1{,}000{,}000}\).

Example Calculation

A 250 W light running 16 hours per day uses 4.0 kWh daily. At $0.15/kWh, that costs $0.60 per day or about $18 per 30-day month. If PPFD is 500 µmol/m²/s, DLI is 500 × 3600 × 16 ÷ 1,000,000 ≈ 28.8 mol/m²/day.

FAQs

What is PPFD?

PPFD measures usable light at the canopy in µmol/m²/s.

What is DLI?

DLI is total daily light, integrating PPFD over time.

Does wattage equal light intensity?

No. PPFD depends on fixture efficiency, optics, and distance.

How accurate are cost estimates?

They are accurate for your inputs but do not include HVAC or time-of-use pricing.

Are results private?

Yes, everything runs locally in your browser.

How it works

This calculator uses energy consumption and DLI formulas to estimate lighting costs and plant-light exposure. All computation runs client-side for privacy and speed.

Disclaimer

Energy costs are estimates and do not include HVAC loads or utility demand charges. Always follow manufacturer guidance for fixture placement and photoperiod scheduling.