The Tiny Particles That Carry Light
Light is all around, everyday. Whether the source is the sun, a lightbulb or a screen, it's around us 24/7 and yet, how often do we really ever stop to think about what it is or where it actually comes from.
Photons
Light is actually made of photons which are elementary particles. They travel through space from the source, whether the sun or a lightbulb, at the speed of light which is 186,000 miles per second. They have no mass which is why they can travel at the so called, cosmic speed limit of the speed of light.
But, these photons carry different amounts of energy depending on their wavelength. The wavelength can go from huge long ones made of metres to short wavelengths of nanometres. The long wavelengths have low energy and the short wavelengths have very high energy.
This variation gives us what we know as, the electromagnetic spectrum of radiation that exists all around us, all the time.
From Radio Waves To Gamma Rays
At one end of the electromagnetic spectrum are radio waves. These have very long wavelengths and relatively low photon energy. At the other end are gamma rays. These have incredibly short wavelengths and very high photon energy.
In between are microwaves, infrared, visible light, ultraviolet and X-rays. Visible light is the light that we can detect with our eyes that make up the rainbow of colour. Therefore considering the extent of this spectrum, visible light is only a tiny part of the entire electromagnetic spectrum.
We don't see most of the light that exists around us. Our eyes have evolved to detect a very narrow range of wavelengths of visible light that happens to be useful for life on Earth.
From The Sun To Your Eyes
The Sun is our main natural source of light. Photons travel from the Sun towards Earth. The whole range of electromagnetic spectrum actually comes towards the Earth from the Sun and further out into space however not all of it reaches the surface. The magentic fields and the ozone layer are barriers through which some of the radiation, particualarly the very harmful ones to life, are absored.
Visible light is the main spectrum that reaches the surface along with some infrared and ultraviolet light. When visible light reaches an object, certain wavelengths are absorbed and others are reflected. Those reflected photons can then enter our eyes.
The eye detects them and converts the information into electrical signals which are sent to the brain. The brain then interprets those signals to give us an image of the world around us. So when you look at a red apple, you aren't directly experiencing "red" travelling through space. You are receiving photons of particular wavelengths which have interacted with the apple, entered your eye and been processed by your nervous system.
The colour is part of the experience created by your brain.
A Very Small Part Of A Very Big Universe
The fascinating thing about light is that the small section we can see is only one tiny part of a much larger electromagnetic world. And we have found so many uses for the other wavelengths of light. Radio waves allow us to communicate. Microwaves can carry information and heat food. Infrared allows us to detect heat. Ultraviolet can damage living tissue. X-rays allow us to see inside the body. Gamma rays carry enormous amounts of energy.
They are all part of the same electromagnetic spectrum. Our eyes just happen to be tuned into one small section of it. And that small section has become incredibly important to us because it is the part of the electromagnetic world that our ancestors evolved to see.
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