1. Absorbance definition is - the ability of a layer of a substance to absorb radiation expressed mathematically as the negative common logarithm of transmittance.

2. Absorbance definition, the capacity of a substance to absorb radiation, expressed as the common logarithm of the reciprocal of the transmittance of the substance

3. This retardation film comprises: a cellulose ester which has a total degree of substitution with acyl groups of 2.0-2.55 and in which when the common logarithm of the absolute molecular weight Mw(a), log[Mw(a)], obtained through analyses by gel permeation chromatography (GPC), low angle laser light scattering (LALLS), and viscosity measurement, is plotted as abscissa and the common logarithm of the intrinsic viscosity Iv(a), log[Iv(a)], obtained through the analyses is plotted as ordinate, the plot has a slope of 0.65-0.85; and a glass-transition-temperature lowering agent having an SP value of 9.0-11.0.