Grow Light Cost Calculator
| LED fixture | 12 hours a day | 14 hours a day | 16 hours a day |
|---|---|---|---|
| Strip light, 20 W | $1.22 | $1.43 | $1.63 |
| Bar light, 45 W | $2.76 | $3.21 | $3.67 |
| Panel, 100 W | $6.12 | $7.14 | $8.16 |
Pick the fixture, the photoperiod and your cents per kWh. The calculator prices the month of light and a full seedling run.
Growing under lights is cheaper than people fear: a modern LED bar draws 20 to 100 watts - a light bulb, not a heater - and the bill follows the timer. Seedlings want 14 to 16 hours, which is a photoperiod decision, not a power decision, and that timer setting is the whole monthly cost.
How to use
- Read the fixture sticker - actual draw in watts, not the equivalent incandescent marketing number.
- Set the photoperiod: 14 to 16 hours for seedlings and leafy starts, 12 for succulents and rest-phase plants.
- Your rate is on the electric bill. The two-month stat covers most indoor seed-starting runs before transplant out. Updates live.
Frequently asked questions
How much does it cost to run a grow light?
A 45-watt bar on 14 hours a day runs about 3 dollars a month at average rates - a 20-watt strip is a dollar, a 100-watt panel about 7. The calculator prices your fixture and rate exactly.
How many hours a day should seedlings be under light?
14 to 16 hours is the consensus for seedlings and most vegetable starts, with a real dark period for rest. More hours do not make stronger plants - leggy, stretched seedlings are usually a distance or duration problem, and the light goes 2 to 4 inches above the leaves.
Do LED grow lights use a lot of electricity?
No - that is their whole point. A 45-watt LED bar runs about 3 dollars a month, where an old 400-watt metal halide would bill near 30 for the same photoperiod. The calculator makes the old-versus-new gap explicit.
Can I use a regular shop light for seedlings?
Yes for starting: a 4,000 to 6,500 K daylight LED shop light at 20 to 40 watts grows perfectly good transplants. Dedicated grow-light spectra matter more for flowering and fruiting indoors than for the six weeks a seedling spends on the bench.
Is it cheaper to start seeds or buy transplants?
Almost always cheaper to start: a tray of six tomato transplants costs what one nursery pot does, and the light bill for the season is single-digit dollars. The real costs are the timer and the discipline, not the electricity.