Weathering and light exposure are important causes of damage to coatings, plastics, inks and other organic materials. This damage includes gloss loss, fading, yellowing, cracking, peeling, embrittlement, loss of tensile strength, and delamination. For many manufacturers, it is crucial to formulate products that can withstand weathering and light exposure. Accelerated weathering and light stability testers are widely used for research and development, quality control and material certification. However, the importance of outdoor testing cannot be overlooked. Outdoor testing is an important supplement to accelerated testing as it provides real time results, and exposes test specimens to complex weathering patterns not easily duplicated in an accelerated laboratory environment. Florida and Arizona are recognized as international benchmarks for outdoor durability testing of materials. Florida has high intensity sunlight, high annual UV, high year-round temperatures, high annual rainfall and high humidity. Arizona features a hot, dry, high UV radiation environment, particularly suited for the weathering of materials under conditions, including: high UV radiation, large temperature fluctuations and low moisture. Accelerated testers provide fast and reproducible results. The most frequently used accelerated weathering testers are the fluorescent UV accelerated weathering tester (ASTM G154) and the xenon arc test chamber (ASTM G155). In recent years, low cost and easy-to-use testers were developed. This paper explores the various weathering test options available, including both outdoor and accelerated methods. Special attention is given to evaluating the two different types of accelerated testers, including their emission spectra, methods of moisture simulation, specialty testing methods, uniformity and practical considerations in tester use. The inherent strengths and weaknesses of each tester will be discussed, including purchase price and operating costs. Guidelines will be given for which tester is generally recommended for a particular material or application. In addition, this paper will briefly compare static array xenon arc testers versus rotating drum xenon arc testers.
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