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Why do chlorophyll makes plants look green if light is not green?
Question Date: 2015-09-16
Answer 1:

Good question. Believe it or not, the light that seems colorless actually has all the colors of the rainbow in it. What’s my evidence? Rainbows!

We call sunlight and other “colorless” light white light. Each color of light is made by tiny packets of light called photons travelling at a different wavelength. Here’s a picture of how different wavelengths are different colors: picture

When we see all the wavelengths together, we don’t see any color. But if we shine that white light through a prism the white light is split into all the colors of the rainbow. The web site above shows this.

You can do this yourself if your teacher has a prism. You may even have glass around your house that makes a rainbow on the wall. We see rainbows in the sky when the light shines through water droplets in the sky at the right angle.

When the white light hits an object, some wavelengths get absorbed. The light energy is usually given off as heat, but pigments like chlorophyll trap the light energy and use it to do the work of making sugar from carbon dioxide and water.

Wavelengths that are not absorbed get reflected. Those are the ones that hit your eye. So if something looks green, which wavelengths are being absorbed and which are being reflected? Here’s a challenge question: Which wavelengths of light is a plant actually using to get its energy?

You may be interested in studying the way light behaves in physics or how plants use light in biology.

Thanks for asking,

Answer 2:

When we see an object of a certain color, it is because the object absorbs light of all colors except for that color, which we see. So, for instance, if we see someone wearing a red shirt, that shirt looks red because it reflects red light, while it absorbs other colors of light.

Chlorophyll is a pigment that absorbs mostly red and blue light and reflects mostly green light, so it appears green to us.

So what does it mean to "absorb" light? Light has wavelike properties, which means it can exist with different wavelengths. Each different wavelength of light corresponds to different energies. Some of those wavelengths correspond to types of light we can see (colored light). Other wavelengths correspond to types of light we can feel (for example infrared, or heat), and others still we cannot see or feel directly but can do damage to our cells (e.g. UV, X-Ray). The collection of wavelengths at which light can possibly exist is called the electromagnetic spectrum.

Visible light -- the range of wavelengths that allows us to see all the colors and objects we can -- actually only comprises a very small portion of the electromagnetic spectrum!

Furthermore, each different wavelength or type of light has a different amount of energy associated with it. When light hits matter, which is comprised of molecules, the molecules in the object can either absorb, reflect, transmit, or scatter the light. Usually some combination of these phenomena occurs, because the kind of light hitting the object usually comes with some range of wavelengths/energies. When light from the sun hits chlorophyll molecules, the red and blue wavelengths excite the electrons in the chlorophyll (i.e. get absorbed) -- that's what drives photosynthesis! The green wavelengths in the sunlight, on the other hand, get scattered and reflected, so we see plant leaves as green!

Answer 3:

What is called 'white' light is actually a mixture of radiation of different wavelengths. These wavelength each have their own cold: from RED to BLUE. Now, Sunlight is a mixture of all these colors and looks “white”. When sunlight falls on a plant, the chemicals in the planet cells ABSORB most of the wavelengths but REFLECT Green. That is the green light which is NOT absorbed but instead is reflected. Plants look green because the reflected light is predominantly composed of radiation of the wavelength that corresponds to GREEN light.

Answer 4:

Chlorophyll reflects green light, and absorbs other colors. Plants look green because green light is reflected away.

Answer 5:

Great question! This story begins with understanding what light is. Unfiltered sunlight arrives on earth in all wavelengths of the visible spectrum (the whole rainbow, purple to red). Plants can only use certain wavelengths of light and reflect all other wavelengths. Chlorophyll absorbs particular wavelengths but reflects green. This reflection of green from plants gives them their green color! This is why when leaves are dying and chlorophyll is breaking down, they change colors (yellow, red, brown)!

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