•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”