NOVELTY - Polymer composition comprises: inorganic or organic near-infrared absorber for absorbing long-wavelength radiation; inorganic or organic reflector for reflecting ultraviolet radiation; inorganic or organic reflector for reflecting e.g. infrared radiation; an optical brightener or fluorescent dye for converting absorbed ultraviolet radiation into visible light or fluorescent light; a photochromic dye for modifying the transmission characteristic of molded part as a function of light intensity; and antimicrobial additive for preventing organic deposits in the photobioreactor.    USE - The polymer composition is useful: for photobioreactors made of plastic molded parts exposed to sunlight or suitable artificial light sources; and as photobioreactors in a suitable plastic molded part (claimed). The photobioreactors are useful as reaction vessels for performing photochemical reactions, for the cultivation of microalgae to produce biofuels such as biodiesel as a form of renewable energy, and for the production of algae concentrates with other applications such as fish farming and production of food additives or as binder or neutralizer of carbon dioxide from exhaust gases of thermal power plants.    ADVANTAGE - The polymer composition: has improved absorption and transmission characteristics and high durability; is light-weight; and prevents or reduces the organic deposits in the photobioreactors.    DETAILED DESCRIPTION - Polymer composition, in addition to the conventional standard additives, comprises: an inorganic or organic near-infrared absorber for absorbing long-wavelength radiation; an inorganic or organic reflector for reflecting ultraviolet radiation; an inorganic or organic reflector for reflecting visible, near-infrared, or infrared radiation; an optical brightener or fluorescent dye for converting the absorbed ultraviolet radiation into visible light or fluorescent light; a photochromic dye for modifying the transmission characteristic of the plastic molded part as a function of light intensity; and an antimicrobial additive for preventing or reducing organic deposits in the photobioreactor. An INDEPENDENT CLAIM is included for the use of the polymer composition as photobioreactors in suitable plastic molded parts, where the wall of the photobioreactor is tubular or plate-shaped.