Simple, fast and accurate procedure is developed for measuring a Trans
formation Function (TF) of a Photochromic Adaptive Filter (PAF). Photo
chromic filters, whose spectral transmittance depends on previous and
immediate radiant exposure and other environmental conditions, require
special methods of spectrophotometry to determine their properties. T
his article describes methodology of characterizing the luminous trans
mittance as a function of light intensity using easy to implement meth
od. Transformation functions of sample filters for different sources o
f radiation and varied light intensity are evaluated. The measuring sy
stem can also be used for fast determination of spatially and spectral
ly uniform light sources with UV spectral component.