Wiktionary
turbidimetry
n. the measurement of turbidity by means of a turbidimeter
Wikipedia
Turbidimetry
Turbidimetry (the name being derived from turbidity) is the process of measuring the loss of intensity of transmitted light due to the scattering effect of particles suspended in it. Light is passed through a filter creating a light of known wavelength which is then passed through a cuvette containing a solution. A photoelectric cell collects the light which passes through the cuvette. A measurement is then given for the amount of absorbed light.
Turbidimetry can be used in biology to find the number of cells in a solution.