The main aspects of photobiological measurements and obtaining action spectra have been considered. It has been shown that the proper use of internationally defined quantities and units in scientific publications promotes the best international communication in the science of photobiology and photochemistry. The accuracy and precision of the applied action spectra, measurement techniques and consideration of exposure geometry are of importance. The factors which influence the quality of the original photobiological research, the possible sources of error and the levels of uncertainty in applying laboratory action spectra to human health risk assessment have to be taken into account.