What Wattage Fluorescent Lights Should I Use for Plants?

Plant Requirements

• When they are in natural sunlight, plants are exposed to many different light wave colors. At one end of the spectrum is red light, while at the other end are the blues. Although natural sunlight contains those colors and more, plants do not need a full range of light waves in order to grow. Foliage plants are able to grow when given mainly blue light waves, which provides what they need for photosynthesis and growth. Plants that flower or fruit, however, must also have light from the red end of the spectrum in order to be able to perform those functions.

Fluorescent Light Quality

• Regular fluorescent light is made up almost entirely of blue light waves. Because of that, it works well to support the growth of foliage plants, and such plants grown with adequate fluorescent lighting will be well-developed, lush and rich green in color. Flowering or fruiting plants of any sort, though, will only grow as foliage plants and will never be able to fully develop due to the lack of red light waves in standard fluorescent lighting.

Intensity

• Light intensity is an important consideration when planning lighting for plants. Intensity can be achieved in several ways. The first way is by using very bright, high wattage bulbs. These bulbs are powerful enough to provide adequate lighting for the plants even if they are mounted on the ceiling. However, the intensity of light drops rapidly with distance, so less powerful lights must be placed closer to the plants. A single or double 40-watt fluorescent light fixture can provide plenty of light for growing foliage plants when placed about 6 inches above the top of the plants.

Duration

• Another factor to be considered when choosing the fluorescent light wattage is to consider the duration of the lighting period. Leaving the lights on longer is another way to provide adequate light to plants. Bulbs that provide less intense light -- those with lower wattage -- must be left on about 16 hours per day in order to give the plants enough light. Bulbs of a higher wattage don't need to be on as many hours per day in order to provide the plants with adequate light.