Personal reflections on monochromators and action spectra for photoreactivation

This is a summary of work done, chiefly by the author, in the mid-20th century, when monochromators were a primary tool in identification of molecules involved in biological effects, much as spectrometers were useful for molecular chemistry in the 19th and early 20th centuries. Monochromator types are discussed, as well as production of action spectra fro the chromophores for photoreactivation of ultraviolet biological effects. Two new types of non-enzymatic photoreactivation were found in prokaryotes, in addition to the classical enzymatic photoreactivation.