Without light, observation is impossible. A realistic minimum of intensity is required (30 lux, with higher values for older people). Contrast, color, surface characteristics, shape and space, motion and stillness can be experienced, but the eye has its limitations in sensing these various kinds of information. The observation of color depends on the composition of the light. Museum lighting has to provide a proper transition from outside to indoor conditions in the first place. Because of the great variability of the daylight in the Netherlands, museums should have an adaptable lighting system. One should keep in mind that the human eye requires an adaptation period of about half an hour when coming from broad daylight to the museum level of 50 lux. During that first half hour, vision is noticeably impaired. Functional lighting serves a purpose on several levels, orientation in the spatial structure, identification of the surrounding objects, visibility of guideposts. Light can be used in accentuating items in an exhibition, even in telling the story of the exhibition. Ergonomically, vision is optimal in a vertical plane at an angle of some 30° below eye level, so that is where the light has to be. A physical property of light is the quadratic decrease of intensity with the distance from the light source. Luminance is the bright appearance of the light source or of its reflection from a glossy surface. Light intensity and luminance should be regarded carefully, because the museum visitor could be confronted with contrasts much too great for convenience. Fixtures have to serve the quality of lighting and have no purpose of their own. Built-in fixtures are preferred, resulting in concealed lighting of a whole room. We are still far away from the situation in which the museum visitor can create his own taste in the lighting of objects, as this idea involves a completely different approach to exhibitions.