Grow light electricity use depends on wattage, hours per day, days per month, and your local electric rate. A small LED seedling shelf may cost only a few dollars per month. A larger grow tent with strong lights, fans, and heat can noticeably raise the bill.
Do not estimate by the product name alone. A light advertised as “1000W equivalent” may use far less actual power. Use the real watt draw from the label or meter.
For choosing a seed-starting light, read Best Grow Lights for Seedlings.
Last updated: June 6, 2026.
Quick Answer
Use this formula: watts / 1000 x hours per day x days x electricity rate = cost. A 40-watt LED running 16 hours per day for 30 days uses 19.2 kWh. At $0.18 per kWh, that costs about $3.46 per month.
Grow Light Electricity Formula
The basic formula is:
watts / 1000 = kilowatts
kilowatts x hours = kilowatt-hours
kilowatt-hours x electric rate = cost
Example:
100 watts / 1000 = 0.1 kW
0.1 kW x 16 hours x 30 days = 48 kWh
48 kWh x $0.18 = $8.64 per month
Use your bill rate for the most accurate estimate. In 2026, the U.S. Energy Information Administration projected average U.S. residential electricity around 18.2 cents per kWh, but rates vary widely by state and utility.
Monthly Cost Examples
| Actual watt draw | Hours per day | kWh per 30 days | Cost at $0.18/kWh |
|---|---|---|---|
| 20 W | 16 | 9.6 | $1.73 |
| 40 W | 16 | 19.2 | $3.46 |
| 100 W | 16 | 48.0 | $8.64 |
| 200 W | 16 | 96.0 | $17.28 |
| 400 W | 12 | 144.0 | $25.92 |
| 600 W | 12 | 216.0 | $38.88 |
These examples are for the light only. Fans, pumps, heaters, humidifiers, and dehumidifiers add more.
Seedling Shelf Cost
A common seedling shelf might use:
- two 40-watt LED shop lights
- 16 hours per day
- 30 days
Calculation:
80 W / 1000 x 16 x 30 = 38.4 kWh
At $0.18 per kWh, that is about $6.91 per month.
That is usually reasonable for starting vegetable seedlings, especially compared with buying many transplants.
Grow Tent Cost
A grow tent can use much more electricity because it may include:
- high-output LED panel
- inline fan
- clip fan
- air pump
- humidifier
- dehumidifier
- heater
The heater or dehumidifier may cost more than the light in some climates. For beginner tent budgets, read Grow Tent Setup Cost for Beginners.
Actual Watts vs Equivalent Watts
Many LED products advertise equivalent wattage. For electricity cost, ignore equivalent wattage and find actual power draw.
Look for:
- “actual watts”
- “power consumption”
- label on power adapter
- manufacturer specification sheet
- plug-in watt meter reading
If a light has dimming, cost changes with the dimmer setting.
Ways to Lower Grow Light Cost
Use these habits:
- grow crops that fit the light footprint
- use reflective shelf surfaces or white walls
- keep lights close enough to plants
- use a timer
- do not run lights 24 hours
- choose efficient LEDs
- start seeds in batches
- avoid heating an oversized space
- retire weak old fluorescent bulbs
Cheap lights are not always cheap if they grow weak plants slowly.
FAQ
Is it expensive to run grow lights?
Small LED grow lights are usually inexpensive to run. Large tents, heat, and long photoperiods can become expensive.
How many hours should grow lights run?
Many seedlings and leafy crops use about 14 to 18 hours per day. Fruiting crops may need strong light for 12 to 16 hours depending on setup.
Should I use a smart plug?
A timer or smart plug is useful because it keeps the schedule consistent and prevents accidental 24-hour operation.
Related Reading
- Best Grow Lights for Seedlings
- Indoor Vegetable Garden Setup
- Grow Tent Setup Cost for Beginners
- Hydroponic Herb Garden for Kitchens