Attenuation of the radiant flux when light is passed through a clear medium.
If light of a suitable wavelength is passed through a sample, part of the energy is transmitted to the molecules. As a result, the emergent beam Φout has less energy than the incident beam Φin
Fig. 2: Absorption
The amount of light absorbed generally follows the Lambert-Beer Law and is therefore proportional to the number of absorbing molecules and the path length traversed L. Absorption spectroscopy; Extinction
If the medium contains turbidity matter, additional attenuation is caused as a result of light scattering. Scattered light
| Terms related to absorption spectroscopy: | |
|---|---|
| Lambert-Beer Law: | $\phi_{\text{out}} = \phi_{\text{in}} \cdot 10^{- \kappa \cdot c \cdot L}$ |
| Absorbance: (previously referred to as "extinction E") |
$A = \log_{10} \left( \frac{ 1 }{ \tau } \right) = \log_{10} \left( \frac{\phi_{\text{in}}}{\phi_{\text{out}}} \right)$ |
| Absorption coefficient: | $a = \left(\frac{A}{L}\right) \quad a = \kappa \cdot c$ |
| Transmittance: | $\tau = \left(\frac{ \phi_{\text{out}} }{ \phi_{\text{in}} }\right)$ |
| $\phi_{\text{out}}$ | Radiant flux (or radiant power), transmitted |
| $\phi_{\text{in}}$ | Radiant power, received |
| $\kappa$ | Relative absorption coefficient (previously referred to as "extinction coefficient ε") |
| $c$ | Concentration in mol/l |
| $L$ | Path length in cm |