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Related to absorbance: spectrophotometer, transmittance


in radiology, a measure of the ability of a medium to absorb radiation, expressed as the logarithm of the quotient of the intensity of the radiation entering the medium divided by that leaving it.

ab·sor·bance (A, A),

spectrophotometry log of the ratio of the radiant power of the incident radiation to the radiant power of the transmitted radiation.


Chemistry A logarithm of the percent transmission of a wavelength of light through a liquid. 
Microbiology A measure of the amount of light absorbed by a suspension of bacteria or an organic solution, measured by spectrophotometry. Absorbance values are used to plot the growth of bacteria in broth and gauge the purity and concentration of molecules in solution.


spectrophotometry 2 minus the log of the percentage transmittance of light.
Synonym(s): extinction (2) , optic density.


a spectrophotometric measurement of the light absorbed by a solution at a particular WAVELENGTH. The absorbance (A) derives from the percentage of light transmitted as follows:

where Io is the incident light intensity and I is the transmitted light intensity. The absorbance is related to the molar absorption coefficient (extinction coefficient) e (cm-1M-1), concentration c (M), and path length l (cm) as follows:

Absorbance can therefore be used to determine the concentration of a substance in solution, to follow conversion of a SUBSTRATE to a product in an enzymic reaction (see ENZYME), and so on.

Absorbance is sometimes referred to as OPTICAL DENSITY, although this term should be used for measurement of light scattering.


A measure of absorption equal to the logarithm to the base 10 of the reciprocal of the transmittance T, for a specified wavelength and expressed as A = −log10 T. Syn. optical density. See optical density; transmittance.
References in periodicals archive ?
After the mixture was incubated at 37 AdegC for 5 min, the absorbance at 560 nm was measured.
(b) Faster saturation of N719 dye on thicker films reflected by lower slope of dye absorbance at 525 nm.
Maximum absorbance was observed at 0.5 mL/min with a steady baseline and reproducible peak height; therefore, the flow rate of 0.5mL/min was employed subsequently.
Thus, it was found that for papers with low absorbance (paper A), the optimum concentration of carbon nanoparticles in the ink composition is 10 mg/mL.
Scavenging effect (%) = [(control absorbance-sample absorbance) / (control absorbance)] x 100
Staphylococcus aureus at acidic pH 4 showed best absorbance capacity after 48 h of incubation (Fig.
For evaluation of the formation constants and molar absorptivity coefficients from absorbance vs [M]/[L] mole ratio data, a non-linear least squares curve fitting program KINFIT was used.
Hence, the efficiency of the microchannel to read absorbance was 0.85 with 0.15 of uncertainty.
where [A.sub.sample] is defined as the absorbance of the sample, [A.sub.blank] is the absorbance of the reagent blank (sample without ABTS), and [A.sub.control] is the absorbance of the control (ABTS without sample).