Photon energy is directly proportional to the wave frequency .
Gamma ray photons have the highest energy ( around a billion electron volts ) , while radio wave photons have very low energy ( around a femtoelectronvolt ) .
Photon energy is directly proportional to the wave frequency , so gamma ray photons have the highest energy ( around a billion electron volts ) , while radio wave photons have very low energy ( around a femtoelectronvolt ) .