How much will my grow light cost to run, and what DLI will my plants receive? Calculate electricity cost, convert PPFD to DLI, or work backward from a target DLI.
Compare schedules, fixture counts, dimmer settings, PPFD values, or electricity rates. The first row is the baseline for cost differences.
| Setup | W/fixture | Fixtures | Dimmer % | Hours | PPFD | Rate | kWh/day | Daily | Monthly | Yearly | DLI | Monthly difference |
|---|
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.
The calculator uses dimensional conversions with your inputs. kWh/day = watts × fixtures × dimmer fraction × hours ÷ 1000, where 70% dimming is entered as 70 and used as 0.70. Cost/day = kWh/day × electricity rate. Cost/month = cost/day × days per month. Cost/year = cost/day × 365.
DLI = PPFD × hours × 0.0036, where PPFD is in µmol/m²/s and DLI is in mol/m²/day. If you do not have a PPFD meter, optional fixture inputs estimate average PPFD as total PPF ÷ grow area in square meters. Total PPF can come from manufacturer PPF per fixture or from actual watts × PPE. This is an average coverage estimate, not a canopy map.
Use actual wall draw watts for electricity cost. Advertised LED equivalent watts, replacement watts, and model numbers may not match real power draw. Average canopy PPFD is better than center PPFD because plants see the whole lit area. Fans, pumps, dehumidifiers, heaters, air conditioning, and time-of-use pricing are excluded so the result stays focused on the grow light.
Inputs: 100 W, one fixture, 16 hours, $0.15/kWh, 200 PPFD.
Result: 1.6 kWh/day, $0.24/day, about $7.20/month, 11.5 DLI.
Interpretation: within a typical seedling or propagation range.
Inputs: 250 W, one fixture, 16 hours, $0.15/kWh, 500 PPFD.
Result: 4.0 kWh/day, $0.60/day, about $18/month, 28.8 DLI.
Interpretation: strong for leafy crops and near fruiting-crop targets.
Inputs: 600 W, one fixture, 12 hours, $0.15/kWh, 900 PPFD.
Result: 7.2 kWh/day, $1.08/day, about $32.40/month, 38.9 DLI.
Interpretation: high-light flowering crops may use it, but heat and cultivar response matter.
Inputs: 200 W, one fixture, 18 hours, $0.15/kWh, 400 PPFD.
Result: 3.6 kWh/day, $0.54/day, about $16.20/month, 25.9 DLI.
Interpretation: a longer vegetative schedule can deliver similar DLI at lower intensity.
June 29, 2026.
Inputs and results are calculated in your browser. The tool does not need a server round trip for the math.
Costs assume a constant electricity rate and linear dimming. DLI assumes constant average PPFD during the light period.
Terminology and DLI framing follow extension horticulture resources.
Use actual wall draw watts. LED equivalent, replacement, or model-name watts may describe brightness positioning, not electricity consumption.
PPF is total photon output from a fixture, PPFD is photon density arriving at the canopy, PPE is fixture efficiency in micromoles per joule, and DLI is the total daily light received per square meter.
Lux can only be roughly converted when the light spectrum is known. A PAR or quantum meter is better for crop-light decisions.
Dimming usually lowers wall draw and PPFD together, so cost and DLI both decrease. The relationship is often close but may not be perfectly linear on every driver.
Use manufacturer PPF divided by grow area as a rough average PPFD, or estimate PPF from watts multiplied by PPE. Real canopy PPFD varies with height, optics, walls, and fixture spacing.
Longer hours can raise DLI at lower PPFD, but crop photoperiod response, heat, and stage limits still matter. Short-day flowering crops may not tolerate long light schedules.
Common indoor schedules include about 16 hours for seedlings, 18 hours for vegetative growth, and 12 hours for flowering photoperiod crops. Match the schedule to crop biology and target DLI.
No. The calculator estimates grow-light electricity only. Add fans, pumps, dehumidifiers, heaters, and air conditioning separately for whole-room cost.
Monthly cost scales directly with the electricity rate. Doubling the cents per kWh doubles the estimated light cost for the same wattage and schedule.
Yes. The calculations run locally in your browser.
Confirm wall draw from the fixture label, power meter, or manufacturer data.
Measure several points instead of relying on the center hotspot.
Dimmed lights usually use less power and deliver less PPFD.
Fixture PPF and efficacy help estimate coverage before buying a light.
Seedlings, leafy greens, fruiting crops, and flowering crops need different DLI ranges.
HVAC, fans, pumps, and dehumidifiers can dominate total grow-room electricity use.
Energy costs are estimates and do not include HVAC loads or utility demand charges. Always follow manufacturer guidance for fixture placement and photoperiod scheduling.
