Light stability and weatherability data is necessary for the selection of new materials and the improvement of existing materials. It also is necessary for estimating the service life of a product. The main causes of material degradation are bright lighting, sunlight, high temperature, and moisture. The importance of natural sunlight testing is often overlooked. Outdoor exposure is used to test the durability and lightfastness of materials and is an important supplement to accelerated laboratory testing. Outdoor testing provides real time results and is versatile. Test specimens can be exposed directly outdoors or behind glass to reproduce an indoor environment in which products are exposed to sunlight through window glass.This paper reviews basic procedures of outdoor weathering and discusses some of the related effects on the durability of materials. Some of the more important testing options and issues are reviewed such as: effect of the exposure angle, mounting methods, behind glass and direct exposures, and the seasonal variability in exposure conditions.
Eric T. Everett, "Natural Outdoor Testing: An Important Component of a Light Stability Testing Program" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP17), 2001, pp 258 - 262, https://doi.org/10.2352/ISSN.2169-4451.2001.17.1.art00055_1