Measurable variables of light absorption

Three measurable variables are available for characterizing the degree of light absorption, i.e. the light intensity absorbed by a dissolved sample substance. These are  

Let Iq be the intensity of light shone into a substance sample and I be the light intensity still present after passage through the sample. Transmission, absorption and extinction may then be defined as follows. 

Transmission T indicates what fraction of the irradiated light intensity (in %) emerges from the sample  

Extinction E is the most frequently used measurable variable for light absorption. It is the decimal logarithm of the ratio of the intensity of the irradiated light (Iq) to the intensity of the light beam leaving the sample solution (I)  

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