Estimate grow light electricity cost from fixture watts, number of lights, daily hours, and your electricity price.
Table of contents
How to use our Grow Light Electricity Cost Calculator
- Choose Rate type. Use Single rate if your price is the same all day, or Peak/off-peak rates if your light schedule crosses two prices.
- Enter Power per light, Number of lights, and Light time per day using the schedule your lights normally run.
- Enter Electricity price for single-rate billing, or enter Peak-rate light time, Peak electricity price, and Off-peak electricity price for split pricing.
- Click Calculate and compare 30-day lighting cost, Daily lighting cost, Yearly lighting cost, and Electricity used per day.
- Sanity-check the output: doubling Number of lights or Light time per day should roughly double the cost if the same Rate type and prices stay in place.
Definitions
Power per light: The electrical power one grow light uses, in watts. Use actual draw if the label or specs list it.
Watt: A unit of power. More watts means the light uses energy faster.
Kilowatt-hour (kWh): A unit of energy used on electric bills. One kWh is the energy from using 1 kilowatt for 1 hour [1].
Electricity price: The amount you pay for each kWh of electricity.
Peak-rate light time: The part of Light time per day that happens during the higher-price electricity period.
Average price paid for the light energy: The blended $ per kWh after the calculator combines peak and off-peak light hours.
Common mistakes and quick fixes
Mistake: Using the LED model name for Power per light when it is not the actual watt draw.
Fix: Use the real Power per light from the label, plug meter, or product specs when available.
Mistake: Entering cents in Electricity price, such as 16 for 16 cents per kWh.
Fix: Enter Electricity price as dollars per kWh, such as 0.16.
Mistake: Setting Peak-rate light time higher than Light time per day.
Fix: Make Peak-rate light time less than or equal to Light time per day.
Mistake: Choosing Rate type as Single rate even though some light hours use Peak electricity price and Off-peak electricity price.
Fix: Choose Peak/off-peak rates so the Average price paid for the light energy is blended from both prices.
Mistake: Comparing 30-day lighting cost to a full electric bill and assuming they should match.
Fix: Remember that 30-day lighting cost includes only the grow lights, not fans, pumps, heaters, HVAC, taxes, or fixed fees.
Limitations & Key Assumptions / Boundary Conditions
- The calculator estimates grow light electricity only. It does not include fans, pumps, heaters, dehumidifiers, air conditioning, taxes, fixed utility fees, or demand charges.
- The 30-day lighting cost uses exactly 30 days. A real billing month may have 28, 29, 30, or 31 days.
- Peak/off-peak rates use the hours and prices you enter. The calculator does not look up your utility schedule or apply tiered billing rules.
- Power per light is treated as constant. Dimming, ballast loss, driver efficiency changes, and lights that cycle on and off are not modeled separately.
- Yearly lighting cost assumes the same daily schedule for 365 days. Seasonal schedule changes can make the real yearly cost different.
- If Light time per day is 0, cost and kWh are 0, and Average price paid for the light energy is not meaningful because no energy was used.
Methodology
How the calculator finds energy use
The calculator first converts total grow light power from watts to kilowatts, then multiplies by Light time per day. Electric bills commonly charge by kilowatt-hours, or kWh [1].
total_power_kw = (Power per light * Number of lights) / 1000
Electricity used per day = total_power_kw * Light time per day
How cost is calculated
In Single rate mode, every light hour uses the same Electricity price.
Daily lighting cost = Electricity used per day * Electricity price
In Peak/off-peak rates mode, the calculator prices peak hours and off-peak hours separately, then adds them.
offpeak_hours_per_day = Light time per day - Peak-rate light time
Daily lighting cost = (total_power_kw * Peak-rate light time * Peak electricity price) + (total_power_kw * offpeak_hours_per_day * Off-peak electricity price)
The 30-day and yearly outputs are direct multiplications of the daily cost.
30-day lighting cost = Daily lighting cost * 30
Yearly lighting cost = Daily lighting cost * 365
The blended rate is calculated only when Electricity used per day is greater than 0.
Average price paid for the light energy = Daily lighting cost / Electricity used per day
For peak/off-peak pricing, the peak share shows how much of the daily cost came from peak-price hours.
Peak-rate share of daily cost = (peak_cost / Daily lighting cost) * 100
Mini-example
Suppose you run two 600 watt lights for 12 hours per day at $0.15 per kWh. Total power is (600 * 2) / 1000 = 1.2 kW. Daily energy is 1.2 * 12 = 14.4 kWh. Daily lighting cost is 14.4 * 0.15 = $2.16. The 30-day lighting cost is $2.16 * 30 = $64.80, and the yearly lighting cost is $2.16 * 365 = $788.40.