turbidimetryor turbidometrya method used to measure the turbidity (cloudiness) of a suspension. Measurement may be made with a spectrophotometer or a colorimeter. As the turbidity of the suspension increases, the amount of transmitted light decreases. The percentage of light transmitted can therefore be correlated with turbidity. The OPTICAL DENSITY of the suspension provides a measure of the decrease in transmitted light. For a given cell type the relationship between optical density and cell concentration is approximately linear. A turbidimeter therefore enables the GROWTH of BACTERIA to be measured. As the bacteria multiply the liquid medium becomes more turbid because of the increased number of cells. Under standardized conditions the concentration of cells in the suspension can be determined from the optical density.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005