UV-VIS Spectroscopy:
The transmittance is the ratio of the source radiation's power exiting the sample, PT , to that incident on the sample, P0 .
Figure 37.04: Schematic diagram showing the radiation passing through a sample; P0 is the radiant power from the source and PT is the radiant power transmitted by the sample. (b) Schematic diagram of light passing through a blank holder with the radiation defined as P0 .
Multiplying the transmittance by 100 gives the percent transmittance, which varies between 100% when no absorption, and 0% for complete absorption. All the detecting methods measure the transmittance of electromagnetic radiation.
An alternative method for expressing the attenuation of electromagnetic radiation is absorbance, A, defined as
Absorbance is the more common unit for expressing the attenuation of radiation, as it is related linearly to the concentration of the sample.