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Why are things the colour they are

Everything we can see has a colour.

Around us, in our homes, at work, in nature, in space - it is universal, everywhere has a colour, of some sort. But have you ever thought about what makes something the colour it is?

The colour of anything we observe depends upon a few factors. Firstly - Everything is made up of electrons and atoms.

How something will look when bathed in light, is governed by these atoms and electrons. Different materials, objects and items have a different make up of atoms and electrons. Any object, by its nature, will, when exposed to light, do one of the following:

Reflection and scattering

Reflection and Scattering of light

Reflected and scattered light

A lot of objects reflect light to some degree, but something that is particularly reflective, has more free electrons that are able to pass from atom to atom with ease.

The light energy that is absorbed by these electrons, is not passed onto to any other atoms. Instead the electrons vibrate and the light energy is sent out of the material at the same frequency as the original light coming in.

Absorbtion

Absorbed light

Absorbed light

When something appears to have no reflection or is opaque, then the incoming light source frequency is the same as, or very close to, the vibration frequency of the electrons in the given material.

The electrons of the material absorb the energy of the light source, and because the light is absorbed, the material or object appears opaque - it has very little or no reflection.

Transmission

Transmitted light

Transmitted light

This occurs when the energy of the incoming light is either much lower or much higher than the energy or frequency required to make the electrons in the particular material vibrate.

Because of this the electrons in an object that appears to be transparent, instead of capturing the light energy, they let the light wave pass through the object/material unchanged, thus the object/material is transparent to that frequency of light.

Refraction

Refracted light

A glass without and with water showing how light is refracted through water

If you have ever put a straw in a drink, then you may have noticed that the straw appears to be bent under the water.The reason for this is Refraction.

If the energy of the incoming light is the same as the vibration frequency of the electrons in the material, the light is able to go deep into the material, and causes small vibrations in the electrons. These vibrations are passed on to the atoms by the electrons, and in turn they send out light waves at the same frequency as the incoming light. Although this happens extremely quickly, some of the light that is inside of the material slows down, but the frequency of the light outside the material stays the same. The result of this is the light inside the material is bent. The angle of the distortion (refraction) depends upon how much the material is able to slow down the light, in this case as in the image above... water.

An example as to why natural objects are coloured

Example of reflected light

A ripe tomato is a good example of reflective light (the shiny bit) and Absorbed light (the red colour)

A good example as to why things have colour is, in the image here of ripe tomatoes.

Tomatoes appear to be Red because when ripe, tomatoes contain a carotenoid known as "Lycopene".

Lycopene is a bright red carotenoid pigment, a phytochemical found not only in tomatoes but also other red fruits.

Lycopene absorbs most of the visible light spectrum, and being red in colour, Lycopene reflects mainly red back to the viewer, thus a ripe tomato appears to be Red.

Conclusion

There are many reasons why things are the colour they are, but mainly it is due to the absorption and the scattering properties of the material being different from that of the incoming wavelengths of the light that illuminate it.

As a further example: we see green leaves or grass as being green because leaves and grass (and other green plants) use Chlorophyll to change light into energy.

Because of its nature and chemical makeup, Chlorophyll absorbs the blue and red colours of the spectrum and reflects the green. The green is reflected back out to the viewer making the grass and leaves appear green.

Following on briefly to how we see colour... the rods and cones of the eye pick up on the particular wavelength and frequency of green and send the message to the brain. Similarly a ripe tomato is red because it reflects rays from the red end of the spectrum and absorbs rays from the blue end.

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Related Colour Topics

Colour properties

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