Visible Light

• Visible light is the light you see every day. It occupies a small part of the electromagnetic spectrum and comes in waves ranging in length from 400 to 700 nanometers (nm), or billionths of a meter.
  
  

Ultraviolet Light

• Another part of the electromagnetic spectrum contains ultraviolet (UV) light. Its waves are shorter, from 1 to 400 nm, than visible light. Because its waves are shorter, UV light also has more energy than visible light.
  
  

Fluorescence

• When UV light falls on some substances, it puts the atoms in the substance temporarily in a higher energy state, like stretching a spring. Fluorescence happens when the atoms release the energy as a glow of visible light.
  
  

Detection

• Substances will glow in different ways from UV light of different wavelengths. Scientists can detect substances by shining known UV light at an unknown material and watching for the tell-tale glow.
  
  

Lighting

• In a fluorescent lamp, electric current runs through a thin mercury vapor. The mercury vapor gives off UV light. A coating of phosphorus on the inside surface of the lamp glows white when the UV light shines on it.