Most houseplants do not need a grow light if they sit in good bright indirect light, but a grow light can fill the gap in a dim room, a windowless space, or a dark winter. A simple setup that extension guidance describes is a full-spectrum LED fixture placed 12 to 24 inches above the foliage, run about 14 hours a day (anywhere from 10 to 16) on a timer. The right distance and the right hours depend on the plant, so watch how it responds.
This guide explains when a grow light actually helps, what to look for, how to set one up, and the mistakes that waste money or burn leaves.
Do You Need a Grow Light?
Check your light before you buy anything. A grow light is for supplementing the light a plant is missing, so first find out how much it is getting. Our guide to bright indirect light shows how to test a spot with a shadow, a window check, or a light meter.
A grow light is most useful when:
- The room has no usable daylight, such as a windowless bathroom or interior hallway.
- The plant sits far from the window. University of Missouri Extension notes that even low-light plants usually do not get enough light more than about 10 feet from an average window.
- Winter has cut your light. Days are shorter and the light is weaker, so a spot that worked in summer may not in January.
- The plant is telling you it needs more. University of Missouri Extension lists long gaps between leaves, smaller-than-normal leaves, pale green stems and foliage, and yellowing, dropping lower leaves as signs of too little light.
If a plant is already in a bright window and growing well, a grow light is unlikely to add much. Moving a plant closer to a window is often the cheaper fix. Our guide to signs a houseplant needs to be relocated explains how to tell.
What to Look For in a Grow Light
Type of light
Iowa State University Extension compares the main options:
- LED: now the go-to light source for many home gardeners. It is more efficient and gives off less heat than fluorescent. Iowa State suggests placing LED fixtures 12 to 24 inches from the plants.
- Fluorescent: also recommended for home use, with T5 tubes preferred for efficiency. Place them about 6 to 12 inches from the plants, and replace the tubes every one to two years as their intensity drops.
- Incandescent: not a good source of supplemental light because of poor efficiency, high heat, short life, and low intensity.
- High-intensity discharge (HID): mostly used in commercial greenhouses and rarely at home.
Spectrum: do you need a purple light?
Plants use wavelengths from both ends of the visible spectrum, mainly red and blue. Many LED grow lights look pink or purple because they emit mostly those colors. Iowa State notes that the color simply reflects LEDs supplying the wavelengths plants use. A full-spectrum white LED fixture is also an option. Standard shop fixtures with full-spectrum bulbs are among the setups extension guidance describes.
Brightness: be careful with lumens
For a standard four-foot LED shop fixture, Iowa State suggests at least 3,000 lumens. It also cautions that lumens alone do not clearly indicate how well plants will grow under an LED fixture. So choose a fixture made for plants, follow the distance guidance, and let your plants show you whether it is working.
How to Set Up a Grow Light
- Hang it above the plant, not beside it. Light should reach the top of the foliage.
- Set the distance. For LED fixtures, Iowa State suggests about 18 inches for a standard shop fixture, with 12 to 24 inches typical. University of Minnesota Extension gives 12 to 24 inches for foliage houseplants and 6 to 12 inches for flowering ones.
- Plug it into a timer. Iowa State recommends a timer so lights go on and off automatically and plants get a regular dark period.
- Set the hours. Iowa State's standard recommendation is 14 hours a day, with an acceptable range of 10 to 16. University of Minnesota Extension suggests 12 to 14 hours for foliage plants and 14 to 16 for flowering ones. Plants should not get light around the clock.
- Make it adjustable. Raise the light as the plant grows, using an adjustable chain or by raising or lowering the pot.
- Consider a reflector. Iowa State suggests white or Mylar-type films to direct light downward, while watching for heat.
- Adjust by watching the plant. Bleached or scorched leaves mean too much light or too close. Spindly growth means too little.
Which Plants Benefit?
University of Minnesota Extension sorts houseplants into low, medium, and high light groups, and a grow light can lift a plant from one level to the next. A plant that tolerates low light, such as a snake plant or a ZZ plant, may be fine without extra light but will grow more slowly in a dim spot. Plants that want bright light, such as many succulents and hoyas, may need a stronger light placed closer to match what a sunny window would give them. Our own care guides say that "low light" still means some natural or grow light, not no light.
Common Mistakes
- Running the light 24 hours a day. Illinois Extension notes that plants need a rest period and should not get more than 16 hours of light.
- Using an ordinary desk-lamp bulb. Incandescent bulbs are inefficient, hot, and weak for plants.
- Buying by lumens alone. Lumens do not tell you how well plants will grow.
- Setting it too far away or too close. Too far gives spindly growth. Too close can scorch leaves.
- Never adjusting it. As the plant grows, the distance changes.
- Expecting a light to fix a watering or pot problem. If leaves are yellow and the soil stays wet, check the roots and drainage first.
From the Greenhouse Bench
Our published care guides repeat one rule that applies to every grow light question: low light still means some natural or grow light, not none. If you are bringing plants in for the cooler months, you may notice that your windows no longer provide what the plants had outside. Our guide to when to bring houseplants inside covers how to move them over gradually, and a grow light is one tool for the dimmer months that follow. Because lower light also slows how fast plants use water, check the soil before you water. Our guide to low-light houseplants for beginners explains how to set expectations.
Frequently Asked Questions
Do I need a special "grow light" bulb?
Not necessarily. Iowa State describes both purpose-made grow lights and standard shop fixtures fitted with full-spectrum bulbs as workable options. What matters is that the light has the wavelengths plants use and that you place it at the right distance.
How many hours a day should a grow light be on?
Iowa State recommends about 14 hours a day, with a range of 10 to 16. University of Minnesota Extension suggests 12 to 14 hours for foliage plants. Use a timer so it runs on a regular schedule.
How close should the light be to my plant?
For LED fixtures, extension guidance gives about 12 to 24 inches. Fluorescent tubes sit closer, about 6 to 12 inches. Adjust if the plant stretches or its leaves look bleached.
Are purple or pink grow lights better than white ones?
Not automatically. Plants mainly use red and blue light, which is why many LED grow lights look purple, but full-spectrum white fixtures are also used. Choose based on distance, output, and how your plants respond.
Can a plant get too much grow light?
Yes. Iowa State warns that too much light can cause leaf scorch or bleached leaves, and too little can cause spindly growth. Adjust the distance and the hours if you see either.
The Short Version
Measure your light first, add a full-spectrum LED about 12 to 24 inches above the plant for roughly 14 hours on a timer, and adjust based on how the plant grows. If you are not sure whether a plant needs it, start by reading our guide to bright indirect light.
Sources: Iowa State University Extension: how to set up supplemental lights, Iowa State University Extension: sources of supplemental light, University of Minnesota Extension, University of Missouri Extension, and University of Illinois Extension.