Our sensory systems respond to only a fraction of the stimulus energies in the environment.  At left we see the auditory spectrum in cycles per second, or Herz (Hz).  Although natural sounds range from a fraction of a Hz to tens of thousands of Hz, we hear only sounds between 20 and 20,000 Hz.
	At left we see wavelengths in the electromagnetic spectrum in meters (I think). As with sounds, we respond only to a very narrow range of wavelengths - a region of the electromagnetic spectrum we call visible light.   Other species can detect wavelengths above and below this region
	Here is the visible spectrum. with wavelengths shown in billionths of a meter (nanometers).  The visual experience we call 'red' is caused by light on the long end of the spectrum, while the experience we call 'blue' comes from light on the short