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Does different color light change the color of a plants petals or the growth?
Question Date: 2013-04-02
Answer 1:

I’m going to start with your second question. Different colors of light do influence plant growth. The light you see outside does not look like it, but it contains all of the colors of the rainbow. We know this because we can separate the light with water droplets or prisms to make rainbows. Each color has its own wavelength. This is hard to explain without a picture, so check out this NASA site:


Colors on the red end of the spectrum are lower frequency wavelengths that have less energy. Colors on the violet (purple) end have more.

So a plant can get more energy if it gets more light from the purple end of the spectrum than if it gets the same amount of light from the red end of the spectrum. This means more photosynthesis and more growth.

There’s more to the story. When light hits an object, it can be absorbed by the object, reflected off the object, pass right through the object (like glass), or bent as it passes through. We’re just going to look at whether the light is absorbed or reflected.

A plant can only use the light energy that it absorbs. The color that we see when we look at a plant is due to the wavelengths that are reflected off the surface of the plant. When we see a green leaf, it’s because all the colors hit the leaf and the green wavelength were reflected back and hit our eyes. All of the other colors were absorbed. This means that green light is pretty useless to the plant.

I do not know of any plants that change their colors (pigments) when they are grown in different types of light. When we look at plants, we usually see the green color of chlorophyll, the main plant pigment. If you live in a place where the trees “change colors” with the seasons then you have seen the other pigments in the leaf that are left behind when the plant stops making chlorophyll for the season. The reds, oranges, and yellows were there all along, they were just hidden by the green.

You can test your ideas about plants for yourself using colored plastic wrap. Look in the aisle of your grocery store where they sell plastic bags. Put soil in small cups and put 2 or 3 seeds in each. Be sure to design a good experiment. Have at least a few cups in each color of wrapping. Make sure that the cups are alike in every other way (don’t put all the red ones by the window, for example). Make careful measurements and write everything down.

If you are interested in questions like these, you may be interested in a career in botany or plant ecology.

Thanks for asking,

Answer 2:

As you may know, plants use light to turn carbon dioxide into sugars necessary for growth in a process called photosynthesis. Sunlight has the full spectrum of different wave lengths of light that represent each possible color of light; this is why when we look through a prism we can see all of the bands of color present in the spectrum: red, orange, yellow, green, blue, indigo and violet. Plants use different colors, which represent different wavelengths, of light for different purposes. Plants appear green to us because they reflect green light rather than absorbing it. In other words, plants don´t use green light for any purpose. The most important colors/wavelengths of light are red and blue light.

While sunlight contains all color of light, the sunlight of the long days of spring and the even longer days of summer is predominately blue. This is the time of year when plants that have been dormant over the winter start to grow and seeds begin to germinate. Plants use blue light for exactly these actions: growth of stems, stalks, leaves and the germination of seeds and seedlings.

As days begin to shorten in the late summer and early fall, the blue light that dominated the spectrum of sunlight is slowly overtaken by red light. Many ripened fruits and vegetables are harvested in the late summer and early fall. Red light is needed for this purpose: flowering and the production of fruit.

So, while different colors of light effect don´t cause flower petals to be a certain color, they do determine when and how the plant will grow (blue light), and when it will flower and produce fruit (red light). So, different colors of light are very important to plants!

Answer 3:

Plants use red light and blue light for photosynthesis, but not green or yellow light.

I don't believe the color of the petals of a flower care much what color the ambient light is, mainly because nearly all plants spend most of their time in white light (white being the color of sunlight). Yellow or orange flowers are colored with carotenoid pigments, and red, blue, or purple flowers use anthocyanin pigments, and these pigments are coded for in the plant's genes. It would have a hard time changing color even if it had reason to.

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