The invention relates to an apparatus, method and system for measuring and optionally detecting an electrical discharge having a discharge magnitude, wherein the electrical discharge causes a corresponding emission of optical radiation. The apparatus embodies the system and method in accordance with the invention, wherein the method comprises measuring electrical discharge by firstly storing pre-determined calibration data comprising calibrated quantitative measurement values associated with magnitudes of electrical discharge and detector parameters corresponding thereto, the detector parameters being operating parameters associated with the optical detector, receiving and processing a particular detector parameter with the stored calibration data to detect an electrical discharge, and determine a quantitative measurement associated with the magnitude of the detected electrical discharge.