"nephelometry using an infrared light source"@en . . "SDN:S04::S041135" . "Method for measuring turbidity using a nephelometer (instrument that measures scattered light at an angle of 90°) equipped with an infrared light source. Nephelometers are calibrated using formazine solutions (reference standard). This method is used as part of the ISO 7027 standard for turbidity measurements."@en . .