Light intensity
= Light intensity
{title2=$I=\langle\mathbf S\rangle\cdot\widehat{\mathbf n}$}
Here <light intensity> means the time-averaged energy flux per perpendicular <area> for <light>. It is the propagation-direction component of the averaged <Poynting vector>. For plane <electromagnetic waves> in the same medium it is proportional to squared <electric field> <wave amplitude>, giving the projection-squared factor in <Malus's law>.