Abstract: There are disclosed plastics materials (110; 520; 640) that include one or more phosphors (210) for absorbing ultraviolet (UV) light (170, 420) and re-radiating (160, 410) the light at a longer wavelength, for example the red wavelengths at 680 nm and 700 nm used by a plant (130) for photosynthesis. Such plastics materials may be used to protect the plastic (110, 500) from UV-induced degradation. In another embodiment, a light source (600) is provided with an encapsulant (640) that contains a phosphor (210) to prevent UV-light from escaping from the light source. Examples of the phosphor (210) are iron activated lithium aluminate phosphor although the phosphor may be based on lattices comprising, for example, aluminates, silicates, aluminosilicates, phosphates or borates or mixtures thereof. The phosphors may include activators/co-activators/sensitizers based on transition metals or lanthanides.