This Test Guideline describes the determining of the ultraviolet-visible (UV-VIS) absorption spectrum of a chemical compound to have some indication of the wavelengths at which the compounds may be susceptible to photochemical degradation. Degradation will depend upon the total energy absorbed in specific wavelength regions. The absence of measurable absorption does not preclude the possibility of photodegradation. This method utilises a double-beam spectrophotometer which records only the absorption differences between the blank (the solvent and all present chemical species other than the test chemical) and test solutions to give the spectrum of the chemical being tested. The test should be carried out at 25°C. The test solutions should be made up in a concentration which will result in at least one absorbance maximum in the range 0.5 to 1.5 units.