Radiation is any energy that can be transmitted without a medium to travel through. Sound is not a radiation, it requires matter to travel through; Light is a radiation.
Ionizing Radiation is a radiation that has enough contained energy in its Photons that when it encounters matter, it adds electrons or removes protons, changing the matter's molecules into ions. This radiation is the type that is dangerous to humans, usually found in the form of X-Rays, Gamma Rays & Ultraviolet Light.
Čerenkov Radiation is the only kind of Radiation that glows on its own without the use of Phosphoresents. It appears in Nuclear Reactors where escaping Photons disrupt the Electromagnetic field of the container of the reactor, giving off a visible cool Blue glow, as seen here [http://upload.wikimedia.org/wikipedia/commons/f/f2/Advanced_Test_Reactor.jpg].
Green glowing things in popular culture came from Phosphorus materials painted onto slabs of Radium, giving a constant green glow as long as the Radium had photons to exeude. The method was sold as Laterns that never went out, although the Radium, half life giving indeed almost infinite photons to illuminate, had a health-impededingly large dosage of Rads.
