Why Windows Aren't Enough in Winter
Our eyes are poor light meters. A spot that looks bright to you may be dim for a plant, and light drops off quickly as you move away from a window. In autumn and winter the sun is lower and days are shorter, so natural light indoors falls further.
Signs that a plant is not getting enough light include stretched growth, pale or smaller leaves, and the loss of lower leaves. Light requirements vary by plant, so check the needs of each species. A phone light-meter app is only a rough guide, but it is better than judging by eye, and it is most useful for comparing one spot with another.
Light fades quickly with distance. Moving a plant even a few feet back from a window can reduce the light it receives noticeably.
Choosing the Right Type of Light
Mississippi State University Extension notes that LED grow lights are color-optimized for plant growth, with low heat output and a very long lifespan, and that cool-white fluorescent lights also provide effective supplemental lighting. LEDs have largely replaced fluorescent tubes for home use.
Lumens, Color Temperature and PPFD
Lumens measure how bright a light looks to people, not how much usable light a plant receives. Color temperature (Kelvin) describes whether light looks warmer or cooler, and does not say how intense it is. When a manufacturer publishes PPFD (photosynthetic photon flux density), which measures the light plants can use, it is a better basis for comparing fixtures than lumens.
Full-spectrum white LEDs are the simplest choice for a mixed shelf of houseplants. Red-and-blue "blurple" lights can work, but their pink-purple glow makes it harder to judge the true color of your plants.
How to Set Up a Grow Light in 5 Steps
- Find out what your plants need. Shade-tolerant foliage plants generally need less light than sun-loving plants such as succulents and flowering plants.
- Check the light you already have. Look at how much natural light reaches the plant at different times of day, so you know how much the grow light needs to add.
- Choose a fixture that covers your growing area. Check the manufacturer's specifications for coverage and for output at different distances.
- Mount it at the recommended distance. Mississippi State University Extension suggests keeping plants within about 1 to 3 feet of the light source, depending on the plant. Fixture power varies a lot, so follow the manufacturer's guidance and adjust based on how the plants respond over a few weeks.
- Put it on a timer. The same source suggests about 12 to 14 hours of light a day for good growth, controlled by a timer so the schedule stays consistent.
Dialing In Distance and Duration
Even a strong light fails if it is too far from the plants or on for too few hours. Most foliage plants do well with roughly 12 to 14 hours of light a day, and plants also need a dark period each day, so avoid running lights 24 hours. A weaker light running for longer is not always equal to a stronger light running for fewer hours, so judge by how the plants respond.
Adjust height in small steps rather than changing everything at once, and watch the leaves for signs such as bleaching or papery patches (too close or too intense) or continued stretching (too little light).
Common Setup Mistakes to Avoid
Small setup errors can hold plants back:
- Ignoring heat. Even LEDs produce some heat close to the diodes. Check the manufacturer's guidance on distance and watch for bleached or papery leaves.
- Using an ordinary household bulb. A standard bulb is not designed to provide the light plants use. Use a fixture intended for plant growth.
- Skipping the timer. An inconsistent schedule is hard on plants. A plug-in timer fixes it.
- Wasting light. Light that misses the plants and hits a dark wall is lost. Light-colored or reflective surfaces behind the shelf can help.
- Placing every plant at the same distance. Light is usually strongest in the middle of a fixture's coverage, so put light-hungry plants there and shade-tolerant plants toward the edges.
- Never adjusting. As natural daylight changes with the seasons, you may need to review your timer and fixture height.
What to Do Next
Look at where your plants are struggling and decide where a light could go. Check the manufacturer's recommended distance before you hang anything, start with a 12-hour schedule, and watch how the plants respond over the next few weeks. New growth that is more compact and a healthier color suggests the setup is working. If growth is still weak, the light may be too weak for that plant, or something else, such as watering or humidity, may need adjusting.
