Formula Malus Law Intensity Polarization angle
$$\class{red}{I} ~=~ \class{red}{I_0} \, \cos(\class{violet}{\varphi})^2$$ $$\class{red}{I} ~=~ \class{red}{I_0} \, \cos(\class{violet}{\varphi})^2$$ $$\class{red}{I_0} ~=~ \frac{\class{red}{I}}{\cos(\class{violet}{\varphi})^2}$$ $$\class{violet}{\varphi} ~=~ \arccos\left( \sqrt{ \frac{\class{red}{I}}{ \class{red}{I_0} } } \right)$$
Intensity
$$ \class{red}{I} $$ Unit $$ \frac{\mathrm{W}}{\mathrm{m}^2} $$ Light intensity after passing through the analyzer.
Initial intensity
$$ \class{red}{I_0} $$ Unit $$ \frac{\mathrm{W}}{\mathrm{m}^2} $$ Light intensity before passing through the polarizer.
Polarization angle
$$ \class{violet}{\varphi} $$ Unit $$ \mathrm{rad} $$ Angle between the polarization direction from the polarizer and analyzer.