Förster resonance energy transfer

Förster resonance energy transfer (FRET) is like two people passing a ball back and forth. The two people are special molecules called "donors" and "acceptors". The ball is energy. When the donor sends energy to the acceptor, some of the energy is lost along the way, like when the ball doesn't get to the acceptor as quickly as it should. FRET helps us figure out how far apart the donor and acceptor are and whether the energy is getting from one to the other.