Optical Density (Molecular Biology)

Optical density, as well as extinction, are somewhat outdated synonyms for absorbance (see Absorption Spectroscopy). The term "optical density" (OD) is still widely used as a measure of the turbidity of liquid cultures of microorganisms, which is a measure of their density. The increase in light scattering that accompanies growth is usually measured at 600 nm and given as OD600.