How to Use a Grow Light for Indoor Plants? | Distance, Duration & Setup

Use a grow light by placing it above your plants at the manufacturer’s recommended distance, running it 12-16 hours daily on a timer, and keeping a dark period.

Getting grow lights right comes down to three moves: set the right height, run it for the right hours, and give plants a dark rest. Most people fail on details—the light hangs too high, or runs around the clock. The fix for using a grow light for indoor plants starts with distance and duration, then locks in a schedule that mimics the sun.

How Far Should a Grow Light Be From Plants?

Distance depends on the light’s intensity and your plant type. LEDs produce little heat, so they can sit closer than fluorescent or HID lights. The goal is delivering usable light at the leaf canopy without scorching. Watch the plant’s response:

• Leggy, pale growth means the light is too far—move it closer.
• Bleached, brown, or curled leaf tips mean it’s too close—raise the light or shorten daily duration.
• Rotate pots weekly so all sides get even light and plants don’t lean toward the source.

Never let foliage touch the fixture. Even an LED runs warm enough to burn leaves on direct contact, so keep a small gap.

How Many Hours Per Day Should a Grow Light Be On?

Most tropical houseplants do well with 12-14 hours of grow light per day, and a common houseplant range is 12-16 hours. Seedlings want more—14-16 hours—to grow stocky rather than spindly. The University of Minnesota Extension emphasizes using a timer so plants get consistent daily totals. The dark period matters as much as the light: plants use darkness for respiration and growth cycles, and running lights 24/7 can stress them. Aim for at least 8 hours of darkness each night. A smart plug makes the schedule effortless—a Kasa Smart Plug, for example, turns the light on at 7 a.m. and off at 9 p.m. automatically.

Matching Light Intensity to Plant Type

Not all plants need the same light strength. Low-light tolerant houseplants like pothos and snake plants thrive with minimal supplemental light, while succulents, flowering plants, and seedlings need considerably more intensity and longer duration. To measure light objectively, use a PAR or PPFD meter like the Apogee MQ 510, or the free Photone smartphone app, which estimates PPFD from your phone’s camera. Measure at the topmost leaf or canopy level—that’s where the plant receives light. One houseplant guide suggests these PPFD targets:

Perceived brightness is a poor guide—a light can look bright yet deliver weak PAR to leaves. Measuring once tells you whether the setup delivers what the plant needs. When natural light is insufficient, the Royal Horticultural Society’s artificial lighting guidance notes that —and that artificial lighting should supplement, not replace, daylight.

Common Grow Light Mistakes to Avoid

Getting the basics right prevents most failures. Here are the mistakes that show up again and again:

• Lights too far away, producing weak, leggy growth.
• Lights too close, scorching leaves or raising leaf temperature.
• No timer, so the schedule drifts and plants get inconsistent light.
• Running 24/7, which skips the essential dark period.
• Never adjusting height as plants grow taller.

Buy a light matched to your space: If comparing options, our tested roundup of the best grow lights for plants breaks down which models handle which setups. Start with the manufacturer’s hanging distance, run the light on a timer for 12-16 hours, and adjust based on what the leaves tell you—observe, move, adjust.