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No — a typical houseplant grow light costs about $1.85 to $7.50 a month to run. A 30 watt LED bar on for 12 hours a day uses 0.36 kilowatt-hours daily, or about 11 kWh a month, which at the US average residential price of roughly 17 cents per kWh reported by the Energy Information Administration as of 2026 comes to $1.85. A 100 watt panel on the same schedule costs about $6.10 a month. Rates vary widely by state, from around 11 cents in parts of the Midwest and South to over 40 cents in Hawaii, so run the numbers on your own bill.
How do you work out your own cost?
One line of arithmetic. Multiply the actual wattage by hours per day, divide by 1,000 to get kilowatt-hours, multiply by 30 for a month, then multiply by your rate per kWh from your utility bill.
So a 45 watt fixture at 14 hours a day: 45 × 14 ÷ 1,000 = 0.63 kWh per day, × 30 = 18.9 kWh per month, × $0.17 = $3.21 a month. The only place people go wrong is the wattage, because the number printed largest on the box is frequently an equivalence claim rather than the power the fixture actually draws.
What do common setups actually cost?
Monthly figures at 12 hours a day, shown at three rates so you can find your own region. Rates are 2026 EIA state ranges — check your bill for the exact figure.
| Fixture | Actual watts | kWh/month | At 12¢ | At 17¢ | At 30¢ |
|---|---|---|---|---|---|
| Single LED bulb over one plant | 9 W | 3.2 | $0.39 | $0.55 | $0.97 |
| Clip-on gooseneck lamp | 15 W | 5.4 | $0.65 | $0.92 | $1.62 |
| Small LED bar, one shelf | 30 W | 10.8 | $1.30 | $1.84 | $3.24 |
| Two-bar plant shelf | 60 W | 21.6 | $2.59 | $3.67 | $6.48 |
| Full panel over a plant rack | 100 W | 36.0 | $4.32 | $6.12 | $10.80 |
| Large multi-shelf setup | 200 W | 72.0 | $8.64 | $12.24 | $21.60 |
| Old T5 fluorescent, two tubes | 108 W | 38.9 | $4.67 | $6.61 | $11.66 |
For comparison, a US household uses roughly 900 kWh a month on average according to EIA residential electricity data, so a 30 watt plant light is around one percent of that — well below a refrigerator, a clothes dryer or a second freezer.
How do you keep the cost down without hurting the plants?
Four levers, and the first two cost nothing.
- Do not run the light longer than the plants can use. Most houseplants saturate at 12 to 14 hours — Illinois Extension advises against more than 16 hours in any case, because plants need a rest period; more light beyond that is spent for nothing and can disrupt plants that respond to day length. The specifics are in how many hours a day a grow light should be on.
- Move the light closer rather than buying a bigger one. Intensity falls off steeply with distance, so halving the gap can double what reaches the leaves at no extra cost — within the limits set out in how far a grow light should be from a plant.
- Put it on a timer or a smart plug. Consistency matters to plants and forgetting matters to the bill. A smart plug adds about a watt of its own, which is trivial against the saving from a reliable schedule.
- Choose LED over fluorescent. Typically 30 to 50 percent less power for the same usable light, with a much longer service life — see LED vs fluorescent grow lights.
A month-by-month breakdown for specific fixtures is in how much it costs to run a grow light per month, and the fixtures owners rate highest for output per watt are in our grow light picks.
We never buy or physically handle the products we rank — recommendations come from aggregated owner reviews and horticultural consensus, described in how we rank.
More from this hub: Houseplants & Indoor Greenery · Can any LED be a grow light? · How much light houseplants need · Best grow lights · How we rank