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United States Department of Agriculture

Agricultural Research Service

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Colored Spectrum
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Can Plants "See" Light?

The Color Spectrum

Image of an rainbow

What is the Color Spectrum?

Think of a RAINBOW with all its magnificent color. The colors that you see in a rainbow make up the visible spectrum. The sunlight is bent by the raindrops in the air that separate the white light into all the colors we can see. Red, orange, yellow, green, blue, indigo, and violet make up the color spectrum. The visible spectrum contains light that can be seen by humans, yet there is light that we cannot see. The light that cannot be seen with the unaided eye includes far-red and ultraviolet rays, both of which can affect plant growth.

How does light travel?

Light is made up of many units of energy called photons and travels in wavelengths at the speed of light (186,000 miles per second). The longer wavelengths such as far-red have less energy than ultraviolet rays. Nothing can travel as fast as LIGHT! 

What does the visible spectrum have to do with plants?

Plants must have light to grow and survive in their environment. The plants specifically use light to make their food in a process called photosynthesis. The light is absorbed by the green pigment chlorophyll, which is located in the leaves of the plant. The actual colors in the visible spectrum that the plant absorbs and uses for photosynthesis are red and blue. The plant reflects green light, and that is what we see when we look at a green plant. Green light is not the only reflected light. For instance, far-red light is also reflected. Far-red is just outside the visible light spectrum. It is not visible to the human eye, but can be sensed by the plant. Far-red wavelengths are important to the plant because of the competition factor in nature. A plant can "SEE" when there are other plants close by because of the increase of far-red wavelengths the other plants reflect. This will then signal the plant to make the necessary adjustments within their system to try to outgrow the others around them since they are competing for sunlight and other resources.


image of the color spectrum


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Last Modified: 8/12/2016
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