The Effect of Light on Plant Growth & Movement


The intensity, quality and duration of light exposure affects plant growth and movement. Plants that grow without light develop long, weak stems, few shoots and narrow leaves. Learn about the effect of light on plant growth and movement so that you can manipulate light exposure to create a thriving indoor or outdoor garden.


Light quantity is the amount of light. In general, the more light a plant receives the more food it can produce using photosynthesis. Food is fuel that allows the plant to grow. However, there is a limit to how much food any plant can produce. Plants also require periods of darkness for growth.


Light quality refers to its wavelength, also known as its color. Sunlight contains the entire color prism. Flourescent, incandescent and grow lights emit different qualities of light depending on the specific bulb. Blue light encourages leaves. Red and blue light in combination encourage flowers. Plants do not absorb green light, which is why they appear green.


Duration is how long a plant is exposed to light. This is known as the photoperiod. Some plants require long periods of darkness and short periods of light to develop flower buds. Others require short periods of darkness and long periods of light to do so. By manipulating a plant's photoperiod you can either encourage it to flower or inhibit flowering.

Plant Movement

Induced or paratonic movement is when plants move in response to outside stimulation. In general, plants bend towards light sources. For this reason, houseplants often appear to be reaching towards windows. Turning houseplants regularly encourages them to bend the other direction, strengthening their stems and giving them a more balanced appearance.

Reaction Time

Plants take a certain amount of time to respond to light with movement. This is called reaction time. Stronger light generally encourages faster reaction time, while weaker light slows reaction time.

Keywords: plants light, light's effect, plant growth

About this Author

Splitting her time between New York's Hudson Valley and Seattle, Fossette Allane has been writing about food, gardening, and culture since 1997. Her work has been published in newspapers and journals including "The Boston Phoenix" and "FENCE," and on various blogs. She has a master's degree in social work from Hunter College and a B.A. in theater from Oberlin College. She currently teaches undergraduates.