what is it called when measuring the absorbency of something
Absorbance is the negative logarithm of the percent transmittance divided by 100. A spectrophotometer can be set to measure either the percent transmittance or the absorbance of a solution. In lab, you will be using a spectrophotometer called the Spectronic 20 or Spec 20 to measure absorbance.
Absorbance spectroscopy, commonly referred to as spectrophotometry, is the analytical technique based on measuring the amount of light absorbed by a sample at a given wavelength.