Grow lights for houseplants: what actually works and what to skip

Not every home has a bright east or south window. Some apartments face north. Some rooms have windows blocked by neighboring buildings or deep overhangs. A grow light solves this. It is not a gimmick or a supplement: a properly placed full-spectrum LED produces light in the same wavelengths plants use for photosynthesis, and a plant grown under one cannot tell the difference from a window. The question is not whether grow lights work. They do. The question is which type to use, how close to place it, and how long to run it.

What type of grow light to use

There are three main types of grow lights. Only one is worth using for houseplants:

• Full-spectrum LED panels or bulbs: The right choice. Full-spectrum LEDs produce the complete range of wavelengths plants use, run cool, use very little electricity, and last 25,000 to 50,000 hours. They come as screw-in bulbs (for existing lamps), clip-on panels, shelf-mounted bars, and freestanding rigs. This is what to buy.
• Fluorescent tubes (T5, T8): Effective but older technology. T5 high-output fluorescent tubes were the standard before LEDs improved. They work well, especially for shelves of low-to-medium light plants. They are bulkier and less energy-efficient than LEDs but perfectly functional.
• Incandescent and standard warm-white LED bulbs: Do not work as grow lights. They produce too much heat relative to light output, and lack the blue and red wavelengths plants need most. A plant under a regular desk lamp will not grow.

The "blurple" grow lights (bright pink/purple panels popular on Amazon) work on the same principle as full-spectrum LEDs but emit only red and blue wavelengths rather than the full spectrum. They are effective for plant growth but produce an unappealing color cast. Full-spectrum white LEDs are a better choice for a living space because they look like normal light.

How close to place the light

Distance is the most critical variable. Light intensity falls off with the square of the distance from the source: a light 12 inches away delivers four times more intensity than the same light 24 inches away. Placing the light too far from the plant is the most common grow light mistake.

• Low-light plants (pothos, ZZ plant, snake plant, peace lily): 12 to 24 inches from the light source is sufficient. These plants are adapted to dim conditions and can thrive even at the lower end of what a grow light produces.
• Medium-light plants (monstera, philodendron, calathea, rubber plant): 6 to 18 inches. The closer end of this range is better for plants that normally prefer a bright indirect window.
• High-light plants (succulents, cacti, herbs, fiddle leaf fig, bird of paradise): 4 to 12 inches. These plants need the most intensity and benefit from the light being as close as the heat output allows. With LEDs this is rarely a concern since they run cool.

A practical test: hold your hand at the plant's leaf level under the light. If you feel significant warmth, the light is too close. With LEDs this is rarely a problem; with older-style fluorescent or HID fixtures, keep more distance.

How many hours per day

Plants need a dark period as much as a light period. Running a grow light 24 hours a day does not produce better results and can stress many plants. The general guideline:

• Low-light plants: 10 to 12 hours per day
• Medium-light plants: 12 to 14 hours per day
• High-light plants and herbs: 14 to 16 hours per day

Use a plug-in timer. Running the light on a consistent schedule (the same hours every day) produces more consistent plant growth than variable timing. A timer also prevents accidentally leaving the light on overnight or forgetting to turn it on.

Which plants respond best to grow lights

Almost all common houseplants can grow under a full-spectrum LED. Some respond particularly well:

• Herbs (basil, mint, parsley) Thrive under 14 to 16 hours of bright grow light. One of the best indoor grow light applications.
• Pothos and philodendron Grow faster and maintain variegation under a grow light than in a dim room. Work well at 12 to 18 inches.
• Succulents and cacti Usually impossible to keep without a very bright window. A grow light close to the plant (4 to 8 inches) solves this entirely.
• Monstera Produces split leaves and grows vigorously under a bright grow light. Place 6 to 12 inches away for best results.
• Snake plant and ZZ plant These already tolerate low light, so even a modest grow light produces noticeably faster growth than a dark corner.
• Fiddle leaf fig Needs intense light. A strong full-spectrum panel placed 6 to 10 inches away can successfully replace the south window this plant normally requires.

Grow light setups that actually work

A few common configurations:

• Clip-on grow light on a shelf: Best for a single plant or small group. Clamps to the shelf above, positions close to the foliage. Easy to adjust height as the plant grows.
• Bar lights under shelving: Long LED bars mounted under each shelf level illuminate the shelf below. A stackable shelving unit with bar lights becomes a fully lit plant wall for a bedroom or office. Very clean setup.
• Freestanding grow light rig: A floor-standing frame with adjustable arms and panels. Covers a large area and works well for large plants that cannot fit on a shelf.
• Full-spectrum screw-in bulb in a directional lamp: The lowest-cost option. A full-spectrum LED screw-in bulb in a desk lamp pointed directly at the plant. Works well for one plant at 12 to 18 inches. Not suitable for high-light plants.

Signs a grow light is working (or not)

A plant responding well to a grow light will produce new growth within a few weeks of being placed under it. The new leaves will emerge at a rate appropriate to the light intensity. Existing leaves may look the same but new growth tells the story.

Signs the light is too far away or too dim: leggy new growth (long stems, small leaves), slow or no growth after several weeks, variegated plants losing their pattern.

Signs the light is too close or too intense: bleached or yellowed leaves at the top, dry tips, leaf curl. Move the light farther away or reduce the daily hours.

If you want to understand what natural light levels look like by comparison, the light level guide explains how to read what a window actually delivers.

Frequently asked questions