24 Mar What is Light?
We are surrounded every day by objects and processes that we don’t often give much thought to. One such process is that of light. You might have heard various scientific terms in relation to light, but do you really know what they mean? Terms such as ‘electromagnetic wave’ are bandied about but unless you can remember everything you learned in high school science class, it’s not going to mean much to you. Here we look at what makes the magic of light:
It actually took quite a long time for scientists to figure out and agree on what light really is. The first experiments were done by Isaac Newton who believed that light consisted of tiny particles emitted from extremely hot objects like the sun. The Dutch scientist, Christiaan Huygens thought that light was a type of wave that vibrated up and down, as well as moving forward. However, neither of these theories were complete.
The link between light, electricity and magnetism first became apparent in Denmark in 1820. Hans Christian Orsted was lecturing on electricity when he noticed a compass needle jumping around whenever he turned a battery on or off. This showed that a changing electric field created a magnetic field. In 1831, Michael Faraday also discovered that the opposite occurred too, a change in a magnetic field creates an electricity field. Finally, it was Scottish scientist James Clerk Maxwell who combined all these findings and developed the theory of ‘electromagnetism’.
His triumph was using this theory to explain the very essence of light. A changing electric field creating a magnetic field is an endless, self-sustaining process that continues to repeat itself and travels extremely fast – the speed of light! Therefore, light is an eternal dance between electricity and magnetism as it speeds through space, locked in an embrace. When you think of light in this way, the stunning large chandeliers that sparkle in your home will seem even more beautiful than they looked before.
The light that humans can see is only a very small section of the electromagnetic spectrum. The reason why we can’t see other wavelengths, such as gamma rays or radio waves is due to the chemistry of our eyes. Our carbon-based form only triggers a chemical reaction when exposed to light in a certain range of the spectrum. Long waves like radio waves don’t carry enough energy to trigger this reaction, whereas short waves like gamma carry too much and cause damage, such as ultraviolet.
The light that we see is also dictated by our evolutionary past. The 400 – 700 nanometre range (the slice of the spectrum that humans can see) travels well under water before being absorbed. As the first eyes evolved in this aquatic environment, it was this light range that held the most evolutionary benefits for life on earth. When you look at an object, the light that enters your eye is an electro-magnetic wave of a certain length. The light enters your retina, causes chemical changes to occur in your cone cells, which your brain then recognises as distinctive colours.