Most houseplant grow lights cost between about £1.50 and £30 a month to run in the UK, depending on their wattage and how long you leave them on. A small LED grow bar over a few plants is genuinely cheap; a large panel over a whole shelf costs more, but still less than most people fear.
The figure that matters is watts, not the size of the light or how bright it looks. Here is how to work out your own running cost, with real examples.
The Formula for Grow Light Running Costs
Electricity is billed per kilowatt-hour (kWh). To find the cost:
watts ÷ 1000 × hours per day × price per kWh = daily cost
At the time of writing, a typical UK rate is around 27p per kWh, though this varies by tariff and changes over time, so check your own bill. Multiply the daily cost by 30 for a rough monthly figure, or by 365 for a year.
What Grow Lights for Houseplants Actually Cost
All of these assume 12 hours a day at 27p per kWh, which is a common houseplant lighting schedule.
- 15W LED grow bar (one or two plants): about 5p a day, roughly £1.50 a month, or £18 a year.
- 45W LED panel or bulb (a small shelf): about 15p a day, roughly £4.40 a month, or £53 a year.
- 150W LED panel (a large shelf or cabinet): about 49p a day, roughly £14.60 a month, or £177 a year.
- 300W LED panel (a big collection or grow tent): about 97p a day, roughly £29 a month, or £355 a year.
Why LED Matters for Running Cost
Every modern houseplant grow light worth buying is LED, and for good reason. LEDs turn far more of the electricity they draw into usable light and waste much less as heat. An older fluorescent or incandescent setup can cost several times more to run for the same growing result. If you are still using anything other than LED, switching will cut both the running cost and the heat near your plants.