Absorbance

Absorbance is the base-10 logarithm of incident light intensity divided by transmitted intensity at a specified wavelength. It quantifies light attenuation by a sample and is commonly related to concentration.

Beer–Lambert law: A relationship stating that absorbance is proportional to path length and concentration under specified conditions. It links absorbance quantitatively to the amount of absorbing substance.
UV–visible spectroscopy: A spectroscopic method that measures ultraviolet and visible light absorbed by a sample. It is the standard instrument-based method for measuring absorbance across wavelengths.
Electromagnetic radiation: Energy propagated through space as coupled electric and magnetic fields. Absorbance describes how matter attenuates this radiation at selected wavelengths.
Absorptance: The fraction of incident radiant energy absorbed by a material. Unlike logarithmic absorbance, absorptance is a fraction of incident energy.
Transmittance: The fraction of incident radiant power that passes through a sample. Absorbance is calculated as the negative base-10 logarithm of transmittance.
Colorimetry: Quantitative analysis based on the color intensity of a sample or reaction product. Colorimetric assays infer analyte concentration from measured absorbance.
Absorption (electromagnetic radiation): The transfer of electromagnetic energy to matter when radiation interacts with it. Absorbance quantifies attenuation associated with absorption, rather than naming the underlying interaction.
Reflectance: The fraction of incident light reflected by a surface or sample. Reflected light is distinct from the transmitted light used in the usual absorbance definition.
Molar attenuation coefficient: A wavelength-dependent measure of how strongly a substance attenuates light per concentration and path length. It sets the absorbance produced by a given concentration and optical path.
Bradford protein assay: A protein-concentration assay in which Coomassie dye binding shifts the dye's absorption spectrum. Its signal is quantified from absorbance near 595 nanometers.

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