A solid in contact with a liquid, in the presence of an electric field, forms an electric double layer. This layer is present at the interface of the solid and liquid and it shields the charged surface of the solid. This electric double layer has an effect on the optical reflectivity of the solid as it changes the elastic light scattering properties. The formation of the electric double layer involves different timescales, such as the relaxation time and the charging time.
The relaxation time we can write as  with  being the Diffusion constant and  the Debye length.
The charging time can be expressed by  where  is the representative system size.
The Debye length is often used as a measure of electric double layer thickness. Measuring the electric double layer with electroreflectance is challenging due to separation caused by conduction electrons.