Gafchromic external beam therapy (EBT) films have been widely used in clinical dosimetric applications due to their high sensitivity to ionizing radiation such as X-ray and electron beams. In 2011, International Specialty Products (ISP) introduced a new generation of films called EBT3 film. The films exhibit color changes from light green to darker color with the increment of absorbed doses of ionizing radiation. The color changes of the films are commonly characterized using flatbed reflective scanner, and subsequently being used to predict the absorbed dose. Besides ionizing radiation, EBT3 films have also been proven to have high sensitivity towards ultraviolet radiation, and hence, make it a promising method in measuring solar ultraviolet radiation exposure. This research book presents a comprehensive visible spectroscopy method in characterizing the color changes of EBT3 films specifically for the measurement of solar ultraviolet exposure. The visible spectroscopy method and analysis presented in this book is also applicable for other types of transparent films for radiation dosimetry.