Friday, 21 August 2015 06:00

Explainer: What is light?

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Dr Davies says he is excited for what the future will reveal as we continue to expand our understanding of and uses for light. Dr Davies says he is excited for what the future will reveal as we continue to expand our understanding of and uses for light.
  • Visible light—the light in the rainbow—a sliver of light waves
  • Light consists of electric vibrating field linked with magnetic vibrating field
  • Mobile phones, speed cameras and remote controls based on the science of light

IS LIGHT a) the sunlight penetrating our atmosphere, b) the flare from a birthday candle, c) radio waves from the distant universe, or d) the microwaves you use to heat dinner?

The answer is: all of the above.

Take an electric field vibrating up-and-down, link it to a magnetic field vibrating left-and-right, and you have electromagnetic energy, otherwise known as light.

All light waves travel at the same speed, rippling through space at 300,000 kilometres per second, but light with different wavelengths—measured as the length of one up-and-down cycle—has different energies.

Most light waves, University of Western Australia astronomer Dr Luke Davies says, are shorter or longer than our eyes are able to see.

“We’ve successfully evolved to see the type of light that’s most useful on Earth,” he says.

“We can only see a really tiny fraction of light.”

On the electromagnetic spectrum

To see just how much light we are missing, we can map light onto a scale called the electromagnetic (EM) spectrum, moving from super-short wavelengths at one end through to mega-long wavelengths at the other.

Visible light—the light that makes up a rainbow—forms just a tiny blip; the shortest visible light waves are violet and blue, stretching through to red, the longest wavelength we’re able to see.

Light waves longer than visible red are lower in energy and classified as infra-red (heat), microwaves or radio waves.

Light waves shorter than visible violet are more energetic and called ultraviolet, X-rays or gamma rays.

It’s a wave, it’s a particle

Just to really complicate things, light is not an ordinary wave.

“When it’s travelling, light acts as a wave, but when it hits something and gives over energy, it acts as a particle,” Dr Davies says.

These packages or particles of light—called photons—have no mass, but their energy and momentum help explain why light is able to act with a force when it collides with other particles.

Putting light to work

We can bend, reflect, gather and observe light.

Called photonics, the science of light has helped us develop mobile phones (radio waves), speed cameras (microwaves), remote controls (infra-red), sterilising lamps (ultraviolet), X-rays, PET scans (gamma rays) and more.

Dr Davies says he is excited for what the future will reveal as we continue to expand our understanding of and uses for light.

“For astronomy, light is the most important thing we have, it’s our only real window into the universe,” he says.

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Read 3229 times Last modified on Thursday, 20 August 2015 09:46