The Effect of Incandescent Light on Plant Growth

Incandescent light bulb

Plants need light to grow. Photosynthesis--the process by which plants convert carbon dioxide and water into carbohydrates in the presence of chlorophyll--requires light. Artificial lighting, including incandescent bulbs, can fill some or all of that need.

Light Duration

How long a plant receives light can be as important as the intensity of the light it receives. During short winter days, incandescent lighting at even low levels can provide the extended light duration some plants need.

The Importance of Color

Different parts of the light spectrum deliver different numbers of photons--energy particles used in photosynthesis. Ultraviolet light provides more energy than red light because the wavelength of ultraviolet light is shorter.

Breaking Down the Numbers

Scientists use this information to measure the amount of light from individual sources that are sufficient to produce photosynthesis. According to Michigan State University floraculturalist Erik Runkle, only about 6 percent to 7 percent of light from an incandescent lamp is useful for this purpose compared to about 22 percent to 27 percent from a cool white flourescent lamp.

Light Intensity

Because less of the light from an incandescent bulb is useful in photosynthesis, growers must use a brighter bulb--one that produces more light--than they would if using other light sources.

Heat Issues

Lamp with plants

Incandescent bulbs--especially bright ones--produce heat. Exposing plants to incandescent light that is placed too close to the plants in an effort to increase the light intensity can scorch tender leaves.

References

• Michigan State University Department of Horticulture: Principles of Light