Accelerated outdoor weathering has a history which extends back at least 50 years. The advantage of this type of testing is that the sun's natural solar energy spectrum is used to irradiate the specimens under test. Since this is an outdoor method, variations in test conditions occur due to the natural seasonal weather differences. Recent improvements in fresnel concentrator accelerated weathering devices such as day and nighttime temperature control, and new moisture cycles are described that minimize seasonal effects.

Since the development of artificial tests in the early 1900's, many types of artificial light sources have been introduced. Improvements in xenon accelerated weathering chambers have enabled development of new test methods utilizing filters that provide a very close approximation of sunlight especially when compared to fluorescent and carbon arc light sources. This paper will also include a description of an advanced air-cooled xenon arc test apparatus for the accelerated exposure of materials.