First, most material degradation occurs because of UV exposure, so maintaining constant UV output is critical to achieving high accuracy, repeatability, and reproducibility. Air temperature is continuously monitored and regulated by opening or closing a damper, which in turn limits the ability of the blower fan to draw air through the chamber. Typically, the Black Panel temperature is measured by a resistance temperature device welded to a metal panel that is painted black and placed in the sample rack. Accelerated Testing Besides allowing precise control of exposure parameters, another important benefit of this type of environmental testing is that it enables acceleration of the weathering process. Obviously, when testing a product designed to withstand ten years of exposure, it is not practical to take that long to perform the experiment.
Accelerated testing is accomplished through two means.
First, the percentage of time a part is exposed to sunlight during a 24-hour period can be increased up to 100 percent. In the real world, even during daylight hours, the changing angle of the sun alters the level of exposure experienced out in the open. Thus, maintaining a noontime light level over an entire day of testing results in far more than a twofold increase in exposure. This can also be accompanied by higher air temperature and humidity. Xenon arc lamp output versus solar radiation spectrum.