Running a grow light costs about $9 to $62 per month for most home setups in the United States, based on fixtures from 100W to 1000W running 12 to 18 hours a day at an average residential rate near 17 cents per kWh. The formula is watts x hours per day / 1,000 x your price per kWh x 30 days. A 400W LED at 18 hours draws 216 kWh a month, which lands near $37.
blurple vs white led for flowering marijuana
What is the formula for monthly grow light cost?
Multiply the fixture's true wattage draw by daily light hours, divide by 1,000 to get kilowatt-hours, then multiply by your electricity rate and 30 days.
Cannabis Seedling Light Schedule and Distance: A Grower's Guide
- 100W LED, 18 hours a day: 54 kWh, about $9 per month
- 240W LED, 18 hours a day: 130 kWh, about $22 per month
- 400W LED, 18 hours a day: 216 kWh, about $37 per month
- 1000W HPS, 12 hours a day: 360 kWh, about $61 per month, closer to $67 once ballast losses are counted
Plug your own rate in rather than the national average. Rates above 20 cents per kWh push a 400W LED past $43 a month.
How Many Grow Lights for 10 Plants
Does LED or HPS cost less to run each month?
LED wins on cost per photon. A 400W LED bar can replace a 600W HPS in a small tent, cutting lighting cost by roughly a third before you count cooling.
cannabis seedling light schedule and distance
HPS converts most of its draw into heat, so exhaust fans and air conditioning run longer. In a sealed room that heat penalty commonly adds 20% to 50% to the total monthly bill.
What raises the bill beyond the light itself?
- Cooling and ventilation: exhaust fans, inline blowers, and portable AC units can match or exceed the light's own draw.
- Driver and ballast losses: budget magnetic ballasts waste about 10% of the power they pull.
- Tiered and time-of-use rates: grow rooms often push a household into a higher price tier, so the marginal kWh costs more than the average.
- Photoperiod changes: switching from 18-hour veg to 12-hour flower cuts daily use by a third overnight.
What should you check before buying a grow light?
- True wall wattage, not the model name. A fixture marketed as 2000W often draws 200W to 250W.
- Efficacy in micromoles per joule. Above 2.5 umol/J is solid, and 2.7 to 3.0 is excellent.
- Dimmability, so you can run lower output in early veg and seedlings.
- Coverage area and hang height for your tent or room footprint.
- Warranty length and whether the driver or board can be replaced separately.
What are common pitfalls?
Buying on advertised wattage is the biggest one, since inflated numbers make efficiency comparisons meaningless. Running high-wattage fixtures on a shared household circuit is another, and a 15-amp branch can only carry about 1,440 watts continuously.
Grow only where state and local law permit, and check plant-count and canopy limits before scaling up equipment.
Frequently asked questions
Is $50 a month a lot for grow lights?
It is typical for a 600W to 1000W setup running a full flower cycle. A 2x2 tent with a 100W to 240W LED usually stays under $25 a month.
Do grow lights add a lot to my electric bill?
Lighting alone adds roughly 10% to 30% for a single-tent home grow. Cooling, fans, and dehumidifiers are what turn a small grow into a noticeable bill jump.
How do I lower my monthly grow light cost?
Switch to a high-efficacy LED, dim during veg, run lights during off-peak hours if your utility offers time-of-use pricing, and seal ducting so conditioned air is not exhausted outdoors.