•Light
 has both wave and particle properties
 –Travels
 like a wave
 –Interacts
 with matter like a particle: 
 “photon”
 –
 •Full explanation
 involves quantum mechanics
 •For most cases we can
 just choose the right “model” from the above
 two choices
 •Photons, unlike particles in other kinds of “radiation,”
   are particles of “pure
 energy”