Jayden Hughes, of Balclutha Primary School, asks :-

How many different types of light are there?

Daniel Schumayer, a physicist at the University of Otago, responded.

We are inundated with radiation. Just to mention a few types: you text your friend with radiowaves, heat up your food with microwaves, see a rainbow via light rays, take a photo of your skeleton with X-rays, and we are unceasingly bombarded with gamma rays from outer space. Interestingly, all these types of radiation are different forms of the same underlying phenomenon: electromagnetic radiation.

So what distinguishes them? On the beach you see water waves coming to shore and with a tape-measure, you can determine the distance between two consecutive crests. This distance is called wavelength. Similarly to water, electric and magnetic fields can also travel as waves and we can measure their wavelengths too. Our radios use waves with a wavelength of a few hundred metres; a microwave oven uses radiation with a wavelength of few centimetres. Electromagnetic radiation visible to us, called light, has a wavelength of roughly one thousandth of a millimetre, while for X-rays this is approximately one millionth of a millimetre. But all these waves are electromagnetic waves. Only their wavelengths are different.

Why is light special then? Only because during evolution our eyes have developed in a way that we perceive electromagnetic radiation within a certain range of wavelengths. Without special gadgets, we cannot "see" radiowaves, microwaves, and many other waves. We are practically "blind" to most types of radiation, and see a very small spectrum of electromagnetic waves: only those with a wavelength between 700 nm (red) and 400 nm (violet), where nm is an abbreviation for nanometre which is a millionth of a millimetre.

Answering your original question: practically infinitely many types of "light" exist, and we distinguish them based on our perception or their use. However, a bee, a snake or an extraterrestrial creature may call other wavelengths "light", depending on what electromagnetic radiation they observe.