Poynting Vector

$\vec{S}$ is the Poynting vector, which corresponds to the direction of the Electromagnetic Wave or its power flow. $\vec{S}=\frac{1}{{\mu }_0}\vec{E}\times \vec{B}$ Where $I$ is Irradiance in $\frac{W}{m^2}$

$I=S_{avg}=\frac{E_{max}{B}_{max}}{2{\mu }_0}=\frac{E_{max}^2}{2{\mu }_{0}c}$ $E=cB$