h (Planck's constant) has units J*s, and f (frequency) has units 1/s. Therefore E=hf has units of Joules. E is the energy of a single photon at that frequency.

h (Planck's constant) has units J*s, and f (frequency) has units 1/s. Therefore E=hf has units of Joules. E is the energy of a single photon at that frequency. It's not a measurement of power.