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ab·sor·bance (A, A),(ab-sōr'bants),
spectrophotometry log of the ratio of the radiant power of the incident radiation to the radiant power of the transmitted radiation.
a number describing the blackening of an x-ray film in any specified location. In general, the optic density is the logarithm of the ratio of incident light intensity to the intensity of light transmitted through that area and is measured with a densitometer.