Book excerpt: Light, Molecules, Reaction and Health offers a comprehensive overview of health-related, light-based processes and systems, paying special attention to molecular photochemistry. Users of photochemical methods and concepts in pharmacology and biomedicine will find detailed information on the basic processes underlying the biological effects of natural and artificial light—from the primary absorption event occurring in an endogenous or exogenous molecule in a biological compartment, to the final pathological or beneficial outcome. By emphasizing novel methods, including nanostructured materials in therapy and diagnostics, this book allows readers to critically interpret existing data with a goal of stimulating new research in phytotherapy and phytomedicine. - Describes the applications of light controlled methods and systems - Combines a clear narrative with practical tables to effectively connect a primary photochemical event with the resulting biological effect - Presents important topics on the analysis of the processes that are initiated by the absorption of light by photoactive compounds in the skin and the eye, as well as low-intensity light therapy, photoimmunotherapy, UV effects, vitamin D production, skin photoaging, and more