Colors of Light Affecting Plant Growth Projects

Plants are affected by the color of light.

Plants are affected not just by light, but by the color of the light as well. The light that comes from the sun looks white or yellow, but it is actually a full spectrum of color. If you take a prism and put it up to the light, it will divide the light into seven distinct colors: red, orange, yellow, green, blue, indigo and violet. Plant growth can actually be manipulated by long-term exposure to isolated colors within the spectrum.

Red and Orange Light

Red is one of the colors that has the most effect on plant growth.

Phytochrome is the group of proteins that allows plants to sense color. Light quality is the wavelength and color from the light source. Red is one of the colors that has the most effect on plant growth. Red and orange light promote maturation and flowering in plants, but red light alone will not make a healthy plant. Red needs blue to make healthy, leafy and flowering plants. If a plant is spindly, it is probably getting too much red or orange light.

Blue Light

Blue light is also important to plants.

Blue light is the second color that produces the largest effect on plants. This color, along with promoting flowering, also is primarily responsible for encouraging leaf growth. Florescent lights are often used with seedlings because they are high in the blue light wave and encourage leafy growth. The blue light controls the stomata in plants, which is located under the surface of the leaves. The stomata regulates the plant's moisture level. Blue light also controls phototropism, which enables the stems of the plants to reach up toward the light source and the roots to grow down in the soil.

Indigo, Violet and Yellow Light

Indigo, violet and yellow light do not have a special function, but simply contribute to the process of photosynthesis. Plants use light to turn carbon dioxide into sugar. These sugars provide the food for the plants to grow. Photosynthesis increases with the temperature, so that is the reason plants grow more in the spring and summer than they do in the fall and winter.

Green Light

Plants look green because they do not absorb green light.

Green light gives plants their color. The human eye sees the light that bounces off things. It enters our brain and photoreceptors called cones distinguish color by identifying different wavelengths of light.
There is a cone for each major color--red, green and blue--we see. Green light bounces off plants because they do not absorb it, so that is why we see green plants.

Light Experiment

A simple science experiment is often done with colored lights and seedlings.

A simple science experiment is often done by students to test the effect of color on plants. Students begin with seven identical lights with different colored bulbs and seven closely related seedlings. They take pictures and label each of the seedlings, making sure the seedlings are as close as possible to the same type and size of plant, planted in the same soil, and watered the same amount. Then, they put these plants in a dark room and spread them far apart, so they cannot be affected by each other's colored light. They place the plants under the lights and leave them for one to two weeks. They observe them every day and record their observations, taking pictures at the end of the experiment. Finally, they compare the beginning pictures with the ending pictures to discover the effect of different colored lights on the plants.

References

• Oregon State: Environmental Factors Affecting Growth
• Ask a Biologist: Seeing Color
• Gardener's Guide: How Does Colored Light Affect Plant Growth
• House Plants: Artificial Light