Intensity

Average power per unit area

$I=\frac{{\bar{n}}_{t}h\nu }{At}$

• ${\bar{n}}_t$ is the average number of photons

$I\equiv ⟨S⟩=\frac{1}{2}c{\epsilon }_0{E}_0^2$

• $S$ is the Poynting vector
• $E_0$ is the max amplitude of the electric field of the electromagnetic wave