Incandescent lights are the traditional type of light bulbs that have been in use in homes for many years. They are used in lamps and built-in light fixtures, and often provide the only source of artificial light in a home. Incandescent lights are not a good choice for growing plants, because they do not provide enough of the three main components of light that plants need. Plants require light that is of sufficient quality, is of adequate duration and has the necessary intensity.
The quality of light refers to what kind of light waves are emitted by a particular light source. In order to grow, plants must have light that contains blue light waves, as these are essential for the proper growth and development of foliage. Flowering plants or those which produce fruits and vegetables need red light waves as well. Incandescent light is almost completely made up of red light waves. The absence of any blue light waves means that plants grown with incandescent light will not develop properly. They will become leggy and spindly, with small, poorly-colored leaves, and eventually will die.
The intensity of light is a determination of how bright it is when it reaches the plant. When dealing with artificial light, the further the light moves from the plant, the less intense it is. Most incandescent light does not provide enough intensity to allow plants to grow. While moving the light closer can help, incandescent lights are very hot, so a plant cannot be placed closer than two feet to the bulb, which limits the intensity.
Duration of Light
The duration of the light refers to how many hours each day the light is on. This is the one area where an incandescent bulb works the same as other light sources. An incandescent light can be set to be on for as many hours per day as desired. A longer period of light can help to make up for a lack of intensity, but because the quality of light is not suitable, plants will still not grow under an incandescent light.
Using Incandescent Light
Plants will not grow when exposed only to incandescent light. However, plants that get some sunlight or are exposed to other light sources, such as fluorescent light, can benefit from the use of supplemental incandescent light. Fluorescent lights provide mostly blue light waves, so the addition of incandescent light will allow indoor plants to bloom, even if they never see the sun. It is not very cost-effective, however, and it is usually better to purchase an efficient grow light for flowering plants than to try to make up for poor light quality through the use of an incandescent bulb.