Currently, visitors to many special exhibitions have to put up with dim lighting of 50 lux and are told that this is necessary to protect the exhibits from overexposure to light. On the other hand no less sensitive exhibits, be it in older or newer museums, are presented in the brightest daylight or in rooms with overhead lighting. Contradictions of this kind are due to inexact and incomplete recommendations on lighting. Systematic light protection is based on cause and effect which can be determined quantitatively. Thus the decision between lighting an exhibit in a manner acceptable to the conservator no longer has to be based overall on the controversial lux values. The decision can and should be made on the basis of the exposure threshold specific to the object at hand, balancing degree of brightness with the period of exposure. The final decision is determined by the visual demonstration of the inevitable changes that are ascertained colorimetrically. All aspects of the specific museum and exhibit must be considered.