meters. 
A lot of other phenomena are identical to light except the wavelength is
different. 
Transparency, Figure 6-5. Longer wavelength: infrared (IR), microwave, radio waves. shorter wavelength: ultraviolet (UV), X-rays, Gamma rays.
How is electromagnetic radiation produced? A; lots of ways. One important
way is blackbody radiation. Hot objects emit light. Hotter objects emit more light.
illustration/demonstration with light bulb.
To talk about production and characteristics of light, we need to introduce a defintion:
a spectrum. Spectrum is intensity of light versus (``is a function of'', in
fancy mathematical language) wavelength.
Graph of intensity of light versus wavelength.