Test EquipmentCharacterizing a UV chamber with mercury lamps for assessment of comparability to natural UV conditions

UV radiation conditions in a UV chamber equipped with four 300-W mercury vapour lamps have been characterized to assess the exposure received by the specimens aged in the chamber. Spectrally resolved measurements were performed on UV radiation emitted by new lamps and lamps operated for 4850 h in the chamber. An intensity decrease of as much as 75% with a strong wavelength dependency was detected. By linking the measurements with independent broadband measurements of the UV radiation field emitted by a single lamp, the UV dose rate distribution on the specimen plane of the chamber was derived. A method for true exposure accumulation estimation, accounting for the fading of the lamps, was developed. Accumulated UV radiation exposures on material samples in the chamber were derived and compared to long-term (1995-2007) average UV exposures received in natural sunshine at Jokioinen, Finland (lat. 60.4°N, long. 23.5°E, 104 m a.s.l.). Acceleration factors for the exposure in the UV chamber were derived in terms of doses integrated over different wavelength ranges. The acceleration factor was found to depend strongly on the wavelength range of the dose considered, presenting an extra challenge to the assessment of the artificial material exposure duration.