Light can be thought of as a wave and, like waves, it can have a “wavelength” defined as the distance between two consecutive wave crests. If we scrunch the wave up so that the wavelength is very short (i.e. the distance between the peaks is small) then many wave crests would pass us by in a given period of time (think of waves pounding the  beach on a stormy day).  Short wavelength light corresponds to light with high energy.

Our eyes are sensitive to light with a very specific and narrow wavelength range.  The colors of the rainbow span that range of “visible” light (i.e. the light we can see with our eyes) from blue (short wavelength or high energy light) to red (long wavelength or low energy light).    The range of wavelengths that corresponds to visible light, however, only spans a teeny-tiny portion of all wavelengths that light can possibly have.  This entire range is known as “the Electromagnetic Spectrum” and is shown in the figure below.

If the distance between the wave crests is long, then only a few wave crests will pass us by in the same period of time.  Long wavelength light, then corresponds to low energy.

The longest wavelength (lowest energy) light is called “Radio light” or, more often “Radio waves”.  Light with slightly higher energy than radio waves (but still lower energy than visible light) is called “infrared light”.  Both Infrared and Radio are, indeed, forms of light!  They are simply of too low energy (long wavelength) to be detected by our eyes.  We can, however, build devices which easily detect light at these wavelengths. 

So, when you listen to the radio in your car, you are NOT hearing radio waves directly.  Instead, your car radio picks up the radio light emitted by the radio station.  The radio receiver in your car then converts this radio wavelength energy into soundwaves which your ear can detect.