3 PrincipleThe scattered and unscattered light energy of a wavelength of 540 nm to 560 nm passing through a test piece cut from a pipe or fitting is measured and expressed as a percentage of the incident light energy on the test piece. 4 Apparatus4.1 Photoelectric cell, used such that the response of the reading … Continue reading ISO 7686 – Plastics Pipes and Fittings – Determination of Opacity – Testing Equipment