Ultraviolet Light and Fluorescence: If you look around you, you see objects of many different colours. What your eyes are seeing are waves of light, but what is it that makes light from a red T-shirt different from light from a blue T-shirt? Light is a type of wave, and we know that one distinguishing property of different types of waves is their wavelength (the distance between wave peaks). This is what make red light different from blue � the red light has a longer wavelength. Human eyes are sensitive to only a very small range of possible wavelengths of light waves. There is a whole spectrum of waves that are not visible to us, but that we make use of in many different ways. For example, radio and television waves are used to transmit signals from the broadcast antenna of your local radio/TV station, which can be picked up by the aerial of a radio or TV set in your community. Another example might be the heat you feel if you stand near a fire � you feel warm because energy is being carried to you by waves that are of a wavelength your eyes cannot see. Light waves that have a wavelength slightly shorter than visible light are called "ultra-violet". It turns out that they also carry slightly more energy than visible light waves. Physicists have studied what matter is made up of at its most fundamental level, and learned that atoms are one of the basic building blocks. We now know that what distinguishes the different chemical elements is that they are made up of atoms with different numbers of electrons in their atoms. By shining ultraviolet light onto certain elements, the energy of the light wave is absorbed by the atoms of that element, and some of that energy can subsequently be re-emitted, but this time with a wavelength that is visible to us. This is called fluorescence. Shining ultraviolet light onto white clothing (perhaps your shirt) is a good example of this. Try it out, and see if you glow!