Most of the light around you is invisible

The human eye is an incredible piece of evolutionary engineering. But the eye is only able to see light of certain wavelengths – and it's blind to much more light than it can see.

Eyes

A whopping 97% of animal species have a complex optical system that allows them to have vision, of one sort or another.

We humans have two types of cells in our eyes that help us perceive light: rods and cones. The cones comes in three types that allow us to detect red, green and blue light. From these three receptors our brain can interpret an incredible palette of colours.

Light is actually a form of energy that travels in waves, and we can place these waves on the electromagnetic spectrum.

Wavelength

Light is measured in wavelengths, which are the distance between the peaks or valleys of the waveform. The electromagnetic scale spans from wavelengths that are measured in nanometres to wavelengths that are, literally, longer than a football pitch.

Radio waves

At one end of the scale we find radio waves – yes, they are in fact a form of light. With wavelengths that can be taller than a house, radio waves can travel vast distances. Because they have low energy, they don’t really interact with the environment and don’t scatter. This means that we can use them to transmit information across continents and even out into space.

Microwaves

Microwaves are a big part of our daily lives. They have wavelengths around a centimetre long and many common devices use microwaves to wirelessly transmit information, including your mobile phone and Leap cards.

And of course, microwave ovens use microwave light to cook food. Microwaves cause water molecules in food to vibrate. It’s this vibration that causes the temperature of the food to rise.

Infrared light

Infrared is just beyond the range of what the human eye can see, and has a wavelength about the thickness of a human hair.

Technology based on infrared light has been in common use in TV remote controls since the early 1980s. But we have thousands of other applications for infrared light, from predicting weather patterns to analysing molecules. The Infrared part of the electromagnetic spectrum that is most associated with heat; almost half of the energy arriving to the Earth from the sun comes as infrared light.

Visible light

This is light with wavelengths of approximately 400 nanometres to 700 nanometres. These may just be numbers to you but actually they describe every colour of the rainbow, from red to violet – all the light that our eyes are able to see.

Ultraviolet

Once we go beyond visible Light, we find ultraviolet. This light has shorter wavelengths – about the size of a single virus particle, so really, really small. It also has more energy than visible light. It's this extra energy that can cause damage to materials it interacts with, including our skin.

Animals

Humans see some parts of the electromagnetic spectrum. Other animals have evolved to see different wavelengths.

Dogs for instance can see colours between yellow and blue – which means that they’re red/green colorblind. Insects have eyes that allows them to see much further on the ultraviolet scale than humans. Many flowers have evolved to have ultraviolet patterns on their petals that act like runway lights for insects. We can only see these hidden patterns using special cameras.

The colour king of the animal kingdom is the mantis shrimp which has 12 different colour receptors in its eyes and can see colours that we can’t even imagine.

X-rays

Even shorter wavelengths have more energy but are also more dangerous and can cause significant damage to materials they encounter. Nevertheless, we have daily applications for them in the fields of medicine, security and, of course, science. The ability of X-rays to pass through soft materials, but not denser objects, is what allows us to produce shadow images of the human skeletal system.

Discovery of the X-ray

Wilhelm Röntgen received the first ever Nobel prize in physics in 1901 for his discovery of the X-ray – a discovery he stumbled upon quite unintentionally.

While conducting another experiment he observed a new form of light that could pass through soft materials. He came up with the name X-ray as a temporary name, an X often being used in mathematics and science to describe something unknown. The name stuck.

Gamma rays

Finally, we come to gamma rays: rays of light far beyond what our eyes can sense. They have a great deal of energy, so much, in fact, that they cause a great deal of damage to human cells when they come in contact with them, destroying strands of DNA. Gamma rays are produced in some nuclear processes. Their production is rare on Earth but common in outer space.

It's amazing to consider that the rainbows that cross the sky are just a tiny, tiny part of a cosmic spectrum of light that is invisible to us.