Light is one of the most familiar things in our lives. We see because we have organs (our eyes) that sense the intensity (brightness) and wavelength (color) of light. We experience light in a variety of other ways as well. For example, we sense radiant heat when our skin is near a warm object. This is due to our skin's reaction to infrared radiation.

We learn almost all of what we know about the world around us from the interaction of the objects in the world with electromagnetic radiation. Often, the word 'light' is used a little more broadly, to include electromagnetic radiation that is just outside the range we can see, in the ultraviolet and infrared.