What is the difference between absorbance and transmittance?
Absorbance is the measure of the quantity of light that a sample
neither transmits nor reflects and is proportional to the concentration of a substance in a solution. On the meter of the Spectronic 20,
the absorbance is displayed on the bottom scale, which is logarithmic.
The transmittance of a sample is the ratio of the intensity of the light that has passed through the sample to the intensity of the light when it entered the sample ( T = Iout / Iin ). The transmittance is displayed as a percentage on the
top scale of the meter of the Spectronic 20.
To convert between the absorbance and transmittance scales, use the equation:
Absorbance = -log (percent transmittance/100)