photometry

As a noun photometry

is (physics) the measurement of various aspects of light, especially its intensity.

As an adjective undefined is

lacking a definition or value.

As nouns the difference between photometry and spectrophotometry

is that photometry is (physics) the measurement of various aspects of light, especially its intensity while spectrophotometry is (physics|analytical chemistry) the quantitative analysis of electromagnetic spectra by use of a spectrophotometer; especially in order to determine the structure or quantity of a substance.

As nouns the difference between taxonomy and photometry

is that taxonomy is the science or the technique used to make a classification while photometry is (physics) the measurement of various aspects of light, especially its intensity.