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Light  
Light is a form of electromagnetic radiation. Yes, believe it or not, you are exposed to radiation everyday - it surrounds you! Visible light, as physicists call it, is just one part of the electromagnetic spectrum.  
   
Electromagnetic Spectrum  
The visible light which allows us to see, radio waves that allow us to listen to songs and watch tv, microwaves that heat our food, and infrared waves that are emitted by warm objects. These forms of radiation make up the electromanetic spectrum. All forms of this spectrum, all the different kinds of radiation, travel at the speed of "light". Actually, you could probably denote it "the speed of radiation". We visualize the radiation as waves. The only difference between a microwave and visible light is that their wavelength (the distance between the 2 peaks of the imaginary wave) is that a microwave is typically feet longer than visible light waves.