How Does Colored Light Affect Growth of Flowering Plants?

Sunlight is actually made up of all of the colors of the rainbow.

If you enjoy learning about plants, you can look at the effects of various colors on plant growth for your science project. Understanding what colored light is and how it affects the growth of flowers and plants can help people choose the correct lighting around indoor plants.

Colors and Wavelengths

When you look at white light, you probably think it is made up of one color -- white. Surprisingly, white light is made up of the whole spectrum of colors. The difference between these colors is based on their wavelengths. Different wavelengths of light affect plants in different ways. The wavelengths that are reflected the most have the smallest impact on the plant, and the wavelengths that are absorbed the most have the largest impact on the plant.

Green Light

Although you may think that green light would have the strongest impact on plant growth (after all, plants are green), it actually is the least effective. The reason that a plant looks green is because when white light hits the plant, the green light is reflected. Very little of the green light is absorbed, which means that it has very little impact on the plant. Therefore, plants that are grown in only green light will not thrive.

Red and Blue Light

Plants are affected most by red light and blue light. More specifically, blue light causes plants to grow strong leaves. Red light on its own does not have a strong impact on plant growth, but when combined with blue light, it can cause improved growth of flowers on the plant. Therefore, for a plant to grow ideally, it should be exposed to light that has plenty of red and blue wavelengths in it.

Impact on Light Choices

Although it may not seem like many people are growing their plants under colored lights, the effects of colored light on plants does have practical applications. Fluorescent cool white lights have a high amount of blue wavelength, so they are often used to strengthen young seedlings. Flowering plants, however, benefit most from broad spectrum fluorescent bulbs, which have high amounts of red wavelength. Although incandescent lights are also high in red wavelengths, they are usually too hot for flowering plants to grow directly beneath them. Another option for indoor gardeners is fluorescent grow-lights, which contain a high mixture of red and blue wavelengths, but they tend to be only about as efficient as ordinary fluorescent lights but much more expensive.

References

• Oregon State University: Light
• Colorado State University: Plant Growth Factors: Light