Spectral considerations of natural and laboratory-simulated sunlight for degradation studies

A need exists in many disciplines to study and evaluate the effects of sunlight upon various materials. Unfortunately, terrestrial solar radiation is not a constant nor is it always practical to use natural sunlight. Therefore, the use of artificially reproduced solar radiation has been in use at least since ca. 1916 when carbon arc lighting was first used to systematically induce the light fading of dyed textiles. Since that time significant improvements in producing artificial sunlight in the laboratory have been made. This paper will explore some of these technologies and the necessary considerations regarding their proper utilization for chemical degradation studies. We first need to understand the characteristics of solar radiation, specifically the sunlight that reaches the earth's surface. The electromagnetic radiation emitted by the sun contains a wide range of wavelengths including ionizing radiation such as gamma and X-rays and non-ionizing radiation which includes the ultraviolet (UV), visible (Vis) and infrared (IR). Fortunately, ionizing radiation does not significantly penetrate the atmosphere.