This document specifies spectroscopic ellipsometry for the determination of optical properties (refractive index n and extinction coefficient k) and the optical classification of different types of amorphous carbon films within the n-k plane. It is applicable to amorphous carbon films deposited by ionized evaporation, sputtering, arc deposition, plasma-assisted chemical vapour deposition, hot filament techniques and others. It does not apply to carbon films modified with metals or silicon, amorphous carbon films that have a gradient of composition/property in the thickness, paints and varnishes.