How Long Should Grow Lights Be On?
Most indoor plants do well with a steady 12 to 16 hours under grow lights. Here is how to set hours by plant type and why a timer matters.
By Ethan Cole
Updated November 2, 2026
How long a grow light should run depends on the plant, how bright the light is, and how much daylight it already gets. Most indoor growers settle on 12 to 16 hours a day, set on a timer so the schedule never changes.
Quick Answer
| Plants | Common daily hours under lights |
|---|---|
| Low-light houseplants (pothos, snake plant, ZZ) | 8 to 12 hours, or as a top-up to window light |
| Most houseplants, monstera, fiddle leaf fig | 12 to 14 hours |
| Seedlings and leafy greens | 14 to 16 hours |
| Succulents and cacti | 12 to 14 hours |
| Fruiting vegetables (tomatoes, peppers) | 14 to 16 hours |
These are common starting points used by indoor growers, not exact rules. Adjust to your plants.
What Makers Say
GE suggests 12 hours a day for its BR30 grow bulb and 18 hours for its A19 bulb and grow fixture. Most lights with timers offer settings from 3 to 20 hours, such as Barrina’s 3/6/12-hour panel timer, Barrina’s 4/9/14-hour pendant timer, and FECiDA’s 4 to 20-hour floor lamp timer.
Barrina Grow Lights for Indoor Plants
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Why a Dark Period Matters
Plants also need darkness each day; many flowering plants time their blooms by the length of the night. Running a light 24 hours a day is rarely useful for houseplants.
Brightness and Hours Trade Off
A dim light for more hours can deliver a similar daily total of light as a brighter light for fewer hours. If your light is weak or far away, longer hours help; if it is strong and close, shorter hours may be enough.
Use a Timer
Steady hours matter more than the exact number. Many grow lights have a repeating timer built in. Note that several SANSI lights, by their listings, reset or cancel the schedule if you switch them off manually or the power cuts out. For lights without a timer, a plug-in outlet timer or smart plug works.
Barrina Hanging Grow Light Bulbs for Indoor Plant
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Window Light Counts
If a plant sits near a window, subtract some daylight hours, or run the grow light in the early morning and evening to extend the day.
Signs to Adjust
- Stretching or pale leaves: more hours or more light
- Bleached spots or crisp edges: fewer hours, lower brightness, or more distance
Also see how far should grow lights be from plants and our full spectrum LED grow light picks.
Who Should Look Elsewhere
Short-day flowering plants, such as Christmas cactus or poinsettia, need long uninterrupted nights to bloom. Follow a plant-specific schedule for those rather than these general hours.
Frequently Asked Questions
Can I leave a grow light on 24 hours?
Some lights can run continuously, but most plants benefit from a daily dark period. A 12 to 16 hour schedule is more common.
How long should grow lights be on for seedlings?
Many growers use 14 to 16 hours for seedlings.
Do grow lights use much electricity?
Wattage x hours x your rate. A 25W pendant for 14 hours uses 0.35 kWh a day.
About the author
Ethan Cole leads research and editing at WikiHomeLED, comparing LED lighting for the home through manufacturer specs, manuals, safety listings and owner feedback. Every product is scored against the criteria on our How We Review page, and picks are updated when models change.