Naturalesa de la llum. Una breu introducció a la fotoquímica

The first lecture of the seminar on Light, Darkness and Living Beings, held in Mataró in March 2015, was devoted to explaining the dual nature of light and the interaction of this electromagnetic radiation with matter, considering mainly the photochemical aspects. This article summarizes the lecture, offering a brief description of the basis of photochemistry and giving some examples of reactions that need light in order to occur. Examples related to biological systems (e.g. plant photosynthesis, vision and vitamin D biosynthesis) and to academic and industrial organic syntheses (e.g. syntheses of pheromones and molecular photoswitches, and light-induced radical chain reactions) are presented.