 The light that we're most familiar with, visible light, starts at a wavelength of around about 700 nanometers for red light, and goes down to something like 400 nanometers for violet light. But in fact that's a very small part of the spectrum that is interesting to us and that we deal with every day in fact, because in the region from that 700 nanometers all the way down to something like a millimeter, that whole region is called the infrared. And it's called that for the not imaginative name that the frequencies are below the red frequencies, and the reason that's so important to us is that that's what we're all emitting. At the kind of temperatures you find on earth, around about 300 Kelvin, that's the main kind of radiation that everything emits, and so you're emitting that, I'm emitting that, that's why some animals can see further into the infrared because that's a very handy thing if you want to figure out where all the animals are. We see in this visible range because that's the main frequencies that the sun's emitting, and so we can see reflected light from the sunlight most easily in that range. Above the violet there's another band called, well I guess this isn't very imaginative either, we call it the ultraviolet, and this goes up to wavelengths of something like a nanometer. And though the sun peaks largely in the visible light, there's still a fair bit of infrared radiation coming off it, and indeed quite a lot of ultraviolet, and this is a little bit tough on our skin and so we have to hide from that. Well above that we have a large band that's called the x-rays, and this might go up to something like a wavelength of a picometer, so very high frequencies indeed if you work out what those frequencies have to be. They're originally called x-rays because when they were discovered no one knew what they were, but it wasn't that long before people realized that this was just yet another kind of electromagnetic radiation fully described by Maxwell's theory. And then above that we have gamma rays, and gamma rays span all the frequencies above that, they can be made lots of different ways. One of the most common ways on earth is by nuclear processes. Now down below the infrared there are all sorts of interesting radiations we use, there's the microwaves, and there the wavelengths go all the way up to about a meter, and these are what's used in microwave ovens, they're also what's used in some kinds of communication, and then down there we also have television, radio, wi-fi, all those kinds of waves are also electromagnetic waves, and below that you have the long wave radio.