Light is important for plant growth. Without it, there is no photosynthesis, and plants cannot grow and thrive. Light is often the most limiting growth factor when growing houseplants, starting seeds, or nurturing any plant indoors.
Frequently the indoor environment does not have enough light for plants to grow and develop well.While indoor plants differ in their lighting requirements, nearly all would benefit from some supplemental lighting during the winter. Many indoor plants benefit from supplemental light year-round.
Once you've determined how much light your plants need (a target DLI) and what type of fixtures you wish to use (LED, fluorescent, etc.), you can build a supplemental light setup perfectly suited to provide the best light for your indoor plants.
Determining the Number of Lights | General Recommendations | Making Adjustments | Light Setup Needs | Examples | Key Terms | More Information
Determining the Number of Lights Needed
The first step to building a supplemental light setup is determining how many lights are needed. There are a few approaches that home gardeners can take to determine how many lights are needed and how they should be set up.
To see acceptable growth and development, most indoor plants have a fairly wide range of acceptable light conditions. This means that for many home gardeners, a high level of accuracy or precision is not needed to grow indoor plants under lights successfully. Because of that, trial and error is the most straightforward (and least intimidating) option for home gardeners.
This approach involves setting up a supplemental light system using some general guidelines and then making adjustments based on how the plants respond.
For gardeners who wish for more precision or to calculate their needs before they begin, more information can be found in this article:How to Determine How Much Supplemental Light to Provide for Indoor Plants.
- Start by setting up lights utilizing one of the general recommendations below.
- Monitor the plant's growth and development over the next several weeks. Adjust according to the recommendations below if acceptable growth is notobserved.
- Continue monitoring growth and fine-tune the setup until the plants show consistent, healthy growth.
General Recommendations for Light Setups
General Supplemental Light Set-Up Recommendations Using Fixtures Manufactured as Grow Lights
Purchase and install an LED or fluorescent grow light as outlined in the directions in the package and leave lights on for 14 hours a day.
General Supplemental Light Set-Up Recommendations Using Readily Available Fixtures Not Manufactured as Grow Lights
LED:Standard, 4-foot, plug-in shop fixture withfull-spectrum (also called "daylight") light, placed 18 inches from the foliage providing at least 3,000 lumens with lights on for 14 hours a day.
Fluorescent:Standard, 4-foot, plug-in,2-bulb shop fixture with each bulb being 40-watt, T5, high output, and full-spectrum (A.K.A. “daylight”) placed 9 inches from the foliage with lights on for 14 hours a day. (Alternative: Instead of "daylight," use one "cool white" and one "warm white" bulb)
How to Make Adjustments When Growth Under Lights is Not Acceptable
| Symptoms Observed | Action Needed | Methods to Make Change |
|---|---|---|
| Increase Light Intensity |
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| Decrease Light Intensity |
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| Adjust the Wavelength of Light Available |
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| Adjust the Day Length |
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What Supplemental Light Setups Need
There are many ways to build a supplemental light system for indoor plants. Regardless of the setup you use, they should all consider these factors.
Adjustable
The distance from the fixture to the foliage can influence theDLIin a significant way. Most fixtures will need to be relatively close to provide the amount of light plants need. Fluorescent fixtures should be 6 to 12 inches from the foliage. LED can be 12 to 24 inches away in most cases. As plants grow, you will need to move the light source. This adjustment can be achieved by moving the light fixture up and down (on an adjustable chain, for example) or by moving the plants up or down (by adding or removing bricks under the pot, for example).
Reflectors
Light emitted by a fixture will radiate out in all directions. Utilizing reflectors to direct light down allows plants to use more of the light emitted from the fixture. Many reflectors also help dissipate the heat created by the fixture.
Reflectors can be used on the walls and floors toget light to more parts of the canopy. Light from reflected surfaces will not be as intense, but more light in more parts of the canopy, even if it's lower in intensity, can be beneficial, especially for plants like vegetables that require very high light levels. Materials that can be used include Mylar or white polymer films/blankets. Be mindful of heat, as some reflective materials can get hot.
Side Light
PPFDcan drop significantly as you get further from the light source. This means that providing light to the entire canopy of taller plants can be difficult. Positioning light vertically around larger plants allows more light to efficiently penetrate the canopy. Side light can be provided by mounting fixtures vertically (LED strips or tapes are easy fixture options).
Timers
While plants benefit from lots of light indoors, they still need a period of darkness to grow properly. For some species, this dark period is essential for flowering and fruiting (photoperiod). Plug all supplemental lights into a timer to automatically turn lights on and off. For most species, 12 to 14 hours is a good length of time for the light to be on.For home gardeners, it is best to have light on for as little as 10 hours and no more than 16 hours a day.
Examples of Supplemental Lights Set-ups
There are many different ways to set up supplemental lights that allow you to consider the important factors listed above.
Purchased Light Shelves, Carts, and Stands
There are many kits or set-ups available that are designed specifically to be used for providing supplemental light to plants. Many feature a stand or shelves that are fully adjustable and include trays to collect water. Most include light fixtures that are LED or fluorescent. Purchased light shelves, carts, and stands are often attractive. Some so much so that you could even use them in a prominent spot in your home without reservation about their appearance. Shelves, carts, and stands are highly functional and easy to use, but they are also expensive on average, costing hundreds of dollars.
Grow Tents
Grow tents are self-contained boxes/frames lined with a reflective material. They are great for containing the mess of soil and water from indoor plants. These "plant boxes" often maximize the use of sidelights and reflective materials. Tents canget warm, so ventilation is important. Most grow tents come with ventilation options, including ductwork and fans. They come in a wide variety of sizes, ranging from a 2-foot cube to something the size of a room. Much like shelves, carts, and stands, they can be expensive.
Build Your Own
Many home gardeners opt for a "build your own" setup. They tend to be very budget-friendly, although they are not always the most attractive option. However, they are highlycustomizable, allowing you to tailor the setup to the space you have available, making it the size, shape, and level of attractiveness you want.
When planning and building your supplemental light setup, be sure it addresses all the factors listed above. Some examples of DIY setups include:
- Adujustable, expanded metal shelving available from home improvement and big box stores. Use trays (like boot trays) to catch water and hang the light with an adjustable chain from the shelves
- Plastic shelving kitswith adjustable lights hanging from shelves.They don't have adjustable shelves, but they are less expensive and contain solid shelves which helps contain soil and water.
- Wood shelving built from 2×4s and plywood can be built to any specifications, allowing it to fit your growing space and accommodate your plants perfectly. They can be bulky and large.
- Other materials to potentially use include PVC pipes, wall-mounted adjustable shelves, closet or garage organization systems, repurposed cabinets, and gridwall or slatwall shelving. As long as you consider all the factors needed, your options are only limited by your creativity!
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Key Terms & Ideas
- Daily Light Integral (DLI)- the amount of PAR delivered over an area in a 24 hour period of time (mol/m2/day). DLIbasically tells you how much photosynthesis can occur.
- Footcandle-A unit of measurement that indicates light intensity defined as the number of lumens over one square foot. (1 fc = 10.76 lux)
- Intensity- Refers to the amount of light produced or emitted. Intensity is measured in several different ways but the most useful for growing plants is PPF and PPFD.
- Kelvin- A unit of measurementthat indicates the approximate color of the light source. Lower numbers are redder in color and higher numbers are bluer.
- Lumens- a measure of the amount of light given off as perceived by the human eye.
- Lux- A unit of measurement that indicates light intensity defined as the number of lumens over one square meter. (lux = lumens/square meter)
- PAR (Photosynthetically Active Radiation)- The specific range of light wavelengths plants use to photosynthesize.
- Photoperiod-The physiological response of a plant (such as flowering) to the length of the night or a dark period.
- Photosynthetic Photon Flux (PPF)- The amount of PAR being provided by the light source. (Essentially, the amount of light being provided that is useful to the plant.) Measured in micromoles per second (µmol/s).
- Photosynthetic Photon Flux Density (PPFD) The amount of PAR being provided over a surface area. (Essentially, theamount of light useful to plants that actually reaches the leaves.) PPFD is measured in micromoles per square meter per second (µmol/m2/s).
- Watts-The amount of energy used by the fixture.
- Wavelengths Used By Plants -Plants use a specific range of wavelengths in the light spectrum to photosynthesize (referred to as PAR: Photosynthetically Active Radiation).Plants primarily use red and blue wavelengths in the visible light spectrum.
More Information
- Growing Indoor Plants Under Supplemental Lights
- Important Considerations for Providing Supplemental Light to Indoor Plants
- Sources of Supplemental Light for Indoor Plants
- How to Determine How Much Supplemental Light to Provide for Indoor Plants
- Lighting and Houseplants (publication)
