How Does Light Color Affect Plant Growth?

Light Triggers Photosynthesis

Plants require sunlight to produce food. Leaves are green because the pigment in them---called the chlorophyll---absorbs all other colors of light and reflects green light. When the chlorophyll absorbs light energy, it triggers the photosynthesis process through which that light energy is converted into sugars. For the plant to grow, it needs to have this process operating at its prime, with the maximum amount of food being made to give the plant the fuel to grow.

Color and Absorption

Chlorophyll requires light at the two far ends of the visible spectrum to activate photosynthesis. By reflecting green and yellow light waves, the chlorophyll does not use these to begin the process. Plants grown under a green-colored bulb will not grow as large as those under red or white light.

Sources of Light

Natural sunlight has a lot of blue and red coloring in it, but these are imperceptible to the human eye. The plant uses blue wavelengths of light to create food for leaf production, and the red and orange wavelengths will encourage flowers. Plants most effectively use sunlight to grow. Fluorescent lights can be used to grow plants before they flower, since this lighting source is full of blue light. Red spectrum lights will encourage flowers to grow. Many incandescent light bulbs have red light, but heat from the bulb being placed too near the plant can cause damage.

References

• Arizona Cooperative Extension: Environmental Factors That Affect Plant Growth
• Oregon Master Gardener Program: Plant Growth and Light
• Estrella Mountain Community College: Photosynthesis