Plants are affected by the amount of light they receive, or its intensity; the color of the light; and the duration of the light. Supplementing sunlight -- or replacing it entirely -- with indoor plant lights can be the perfect way to encourage the health of your plants, as well as sneak in a "fourth" growing season. Here's what you need to know.
Knowing Your Plant's Light Needs
Before you begin to think about using plant lights, research how much sunlight your plants need. Give a plant too much sun and it will look bleached, pale, or event burned; too few hours and it will have thin leaves and elongated shoots. Some plants require about a half day of light, while others need up to 18 hours of light each day; the latter include vegetables, which will get pale without sufficient light. Still others, such as African violets, need only about eight hours of light per day year-round.
Many indoor plants might get a few hours of direct sun each day, but the angle at which the sun hits a window can be undependable. And natural light isn't strong or long enough to grow herbs or vegetables indoors.
If you have an indoor plant in low light, adding supplemental indoor plant lights can help it stay vigorous and blooming. If you are trying to grow off-season herbs or veggies, you'll need a more formal setup, such as a table with grow lights suspended above.
Choosing the Right Intensity
The watts of the bulb as well as the distance from plant light source to plant determines the intensity of light you provide. Plants used to shady environments don't need as much light; those native to hotter, drier climates might require more intense illumination. For example, African violets can be about a foot away from a light source, and the indoor houseplant philodendron can be up to 3 feet away. But vegetables need a much higher light intensity to produce crops.
Choosing the Right Bulb Color
Sunlight is actually light in a range of colors, called a full spectrum. Plants grow best when they receive that full spectrum, which only the sun can provide. Artificial lights have a narrower range of color than true sunlight. That's why it's important to know the colors of supplemental light you are creating. Lightbulbs typically are blue (cool) or red (warm) in cast. To achieve the best results with indoor plant lights, supply both colors.
Choosing the Right Bulbs
Fluorescent bulbs produce lots of light, are cool to the touch, and are relatively inexpensive. They are available in a range of colors. Indoor plant lights often come in long tubes. If you use fluorescents, consider choosing one of two solutions: Pair a cool-color bulb with a warm-color bulb, or buy full-spectrum fluorescent bulbs.
Leaf lettuce, spinach, and herbs, as well as African violets and succulents, will do well under fluorescent lamps. The trick to using these lights successfully is to keep fluorescent bulbs very close -- no farther than 6 inches away -- to the tops of the plants. Because the tubes are relatively cool, you do not have to worry about burning plants unless they are touching the bulb. You should also rotate plants from the center of the bulb to the edges weekly. In addition, clean your fluorescent bulbs each month to maintain the optimum level of light.
High-intensity discharge (HID) lights are indoor plant light powerhouses, emitting twice the light of incandescents or fluorescents for the same energy cost. They're also more expensive and burn brightly enough that they are usually not suitable for an everyday room in your house. They come in several types:
-- Metal halide lamps offer the best spectrum for the largest number of plants and work especially well if no natural light is available. They are bluish white.
-- High-pressure sodium lamps are great for flowering plants that need extremely bright light; they are yellow-orange.
To achieve optimum HID effect, use an indoor plant light fixture that combines the two types and enables you to turn off one bulb at a time. That way you can alternate the kind of indoor light your plant receives.
Combining Sunlight and Supplemental Plant Lights
If your plant receives a good quantity of natural light and doesn't have high light requirements, it might need just a few hours of supplemental light each day. Watch your plants and adjust the length of lighting time to compensate for the sun's intensity and duration. But if your plants are grown under indoor plant lights alone, they might need 8-16 hours of lighting every day. It's best to rely on a timer to ensure your plants get the right amount of light.
A Note About Incandescents and LEDs
Incandescent bulbs are not suitable for supplemental plant lights; instead, use them to highlight an indoor potted plant. And any incandescent bulb must be placed at least 24 inches away from the plant to avoid burning it.
There are a few LED plant lights on the market; it's a light source that's incredibly energy-efficient but also fairly expensive and with limited color range.