Every living organism is a complex construction in which each element is both part of a larger structure and support for a smaller one. Each scale contributes to a specific effect, and any modification at one level can influence the final outcome. We will indeed see that the interactions between light and living organisms occur within a broad range, from molecular or even atomic interactions at the nanometer scale to shading effects at the macroscopic scale. At each of these levels, interactions occur simultaneously across multiple domains beyond optics, such as mechanics, thermodynamics, fluid dynamics, and aerodynamics. It is therefore practically impossible to focus solely on light when studying natural structures, as multifunctionality is a key consideration. Organisms face numerous constraints, including physicochemical factors (e.g., radiation, pressure, temperature, acidity, humidity) and biological factors (e.g., search for partners, avoidance of predators, inter- and intraspecific communication). Where relevant, the non-optical functions of these structures will be presented (Fig. 4.1).