Sunlight contains ultra-violet (UV) rays which cause rapid deterioration of some foods (especially oils and fatty foods) or specific components of a food such as certain vitamins. UV can also cause packaging materials to fade or to become brittle and lose their properties (for example polythene in Section 3.2.2). In general all foods should be stored in the shade away from direct sunlight. Electric lights do not have the same effects on foods because they do not contain the UV component.