Sunlight (solar radiation) provides many beneficial contributions to mankind, including warmth and energy, vision and photoresponses, photosynthesis, and vitamin D synthesis. Along with these positive benefits attributed to solar radiation, there are also adverse effects. A particular adverse effect of current interest and concern which is addressed in this module, is over-exposure of human skin to solar radiation. The module is divided into four main topical categories: (1) the nature of, and how to detect, the presence and/or absence of radiation; (2) atmospheric filtering of solar radiation (considering photo ionization and photo disassociation); (3) adverse effects on human skin of over-exposure to solar radiation; and (4) commercially available products which claim to protect against over-exposure, and how to test the effectiveness of these products. Included within these categories are activities in which students build a spectroscope; measure the wavelength of radiation observed with the spectroscope; and use the instrument to establish the existence of ultraviolet radiation, observe broad band absorption, and observe radiation absorbed by commercially available sunscreens. The module, which contains the equivalent of 1 week's work for introductory college or advanced high school physics courses, concludes with a summary section. Suggestions for further study and discussion questions are included in this section. (JN)