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The absorbance of a material that has only one absorbing species also depends on the pathlength and the concentration of the species, according to the Beer–Lambert law =, where ε is the molar absorption coefficient of that material; c is the molar concentration of those species; ℓ is the path length.
Absorbance is defined as "the logarithm of the ratio of incident to transmitted radiant power through a sample (excluding the effects on cell walls)". [1] Alternatively, for samples which scatter light, absorbance may be defined as "the negative logarithm of one minus absorptance, as measured on a uniform sample". [2]
Variable pathlength absorption spectroscopy uses a determined slope to calculate concentration. As stated above this is a product of the molar absorptivity and the concentration. Since the actual absorbance value is taken at many data points at equal intervals, background subtraction is generally unnecessary.
The decadic absorbance of a scattering sample is defined as −log 10 (R+T) or −log 10 (1−A). For a non scattering sample, R = 0, and the expression becomes −log 10 T or log( 1 / T ), which is more familiar. In a non-scattering sample, the absorbance has the property that the numerical value is proportional to sample thickness.
B λ (T) is the Planck function for temperature T and wavelength λ (units: power/area/solid angle/wavelength - e.g. watts/cm 2 /sr/cm) I λ is the spectral intensity of the radiation entering the increment ds with the same units as B λ (T) This equation and various equivalent expressions are known as Schwarzschild's equation.
It is found that the value of k(λ) in the deep UV wavelength range is of the order of k = 3 × 10 −4, and this small non-zero value is consistent with T = 0 in the deep UV. Ex. 3: Reflectance and transmittance spectra in 190–1000nm range of ITO deposited on the glass substrate described above, plus the n ( λ ) and k ( λ ) spectra of the ...
T — Radiant flux transmitted by a surface, divided by that received by that surface. Spectral hemispherical transmittance: T ν T λ — Spectral flux transmitted by a surface, divided by that received by that surface. Directional transmittance: T Ω — Radiance transmitted by a surface, divided by that received by that surface. Spectral ...
This should not be confused with "absorbance". Spectral hemispherical absorptance: A ν A λ — Spectral flux absorbed by a surface, divided by that received by that surface. This should not be confused with "spectral absorbance". Directional absorptance: A Ω — Radiance absorbed by a surface, divided by the radiance incident onto that surface.