Lighting can pose the greatest obstacle when trying to grow plants successfully indoors, especially if you don't have a window that lets in plenty of sunshine. Plants require more time in the light when grown under plant lights, but determining how much depends on individual plant needs, the light intensity and the type of lighting you provide.
Lighting can pose the greatest obstacle when trying to grow plants successfully indoors, especially if you don't have a window that lets in plenty of sunshine. Plants require more time in the light when grown under plant lights, but determining how much depends on individual plant needs, the light intensity and the type of lighting you provide.
The quality of light impacts how much light a plant needs. Plants primarily need light on the red and blue spectrums, which are best provided by using a full-spectrum fluorescent bulb or bulb labeled as a grow light. Another option is to use two fluorescent tubes, one warm white and one cool white, to provide a more complete spectrum. Incandescent bulbs only provide light on the red spectrum. They also have a shorter life and produce substantial heat, which can damage heat-sensitive plants.
Light intensity is measured in foot candles. Most houseplants require between 50 and 1,000 foot candles from either artificial sources or from sunlight. If the plant only requires low light or receives some light from a window, regular lighting from ambient light fixtures in the room may be sufficient. Plants that require medium light require at least 250 foot candles, so they will grow better with a small grow light fixture if they aren't near a sunny window.
Seedlings, especially vegetables and other that thrive in full sun, require 1,000 foot candles or more of light intensity, so intensive grow light fixtures that contain at least four light tubes are necessary for healthiest growth. Light intensity also varies depending on how close the plants sit to the light. For example, plants sitting 6 inches beneath a two-light fixture receive 500 foot candles, while those setting 3 feet from the light source only receive 60.
For best growth, place seedlings and high-light beneath a four-tube fixture containing full-spectrum lights. Set them about 6 inches beneath the lights so they can receive about 900 foot candles of light intensity. You can use a two-tube fixture, but the light intensity will be less and the plants may not grow as well. Seedlings require about 16 to 18 hours of artificial light daily. Ensure they receive even lighting and the maximum light intensity by placing reflectors around the light fixture, which will reflect all the light onto the tops and sides of the plants.
Most common houseplants can grow well with 12 to 14 hours of artificial light if they aren't receiving any sunlight. Medium-light plants require about six hours of daily sunlight, so they benefit from a higher light intensity and do best when set no more than 1 foot away from the lights. Low-light plants typically grow well in shade or with less than four hours of direct sun, so you can set them 2 to 3 feet from the fixture.
Although these plants have differing intensity needs, the amount of lighting time is the same when it's supplied by artificial means. If your plants receive some daytime sun but less than fits their needs, such as from a nearby window, provide them with an additional two to six hours of artificial light in the evening.
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