Activation spectra: Techniques and applications to stabilization and stability testing of materials

The activation spectrum of a material represents the relative amount of damage caused by individual spectral regions of the source to which the material is exposed. Experimental techniques used to determine activation spectra include (1) narrow-band radiation utilizing interference filters or a grating or prism spectrograph and (2) polychromatic radiation with sharp cut-on UV/visible transmitting glass filters to define the relative effects of radiation by individual spectral regions during exposure to all wavelengths longer than the cut-on of the filter. The spectral effects of radiation on a material are determined by measurement of spectral changes, i.e., by UV, visible or infrared spectroscopy, and, if sample size permits, by changes in physical properties. Applications of activation spectra include the development of light stable materials, the design of meaningful light stability tests, timing of exposures based on actinic radiation and prediction of service life by providing a means of determining effective dosage. Examples are given to demonstrate many of the applications of activation spectra and comparison is made with action spectra which represent the wavelength sensitivity of a material independent of the spectral emission properties of the radiation source.