There is a growing body of evidence that man actually needs daylight, since the cycle of daylight somehow plays a vital role in the maintenance of the body's circadian rhythms. The change of light during the day is a fundamental constant by which the human body maintains its relationship to the environment. Thus, too much artificial light can create a rift between a person and his surroundings, and upset the human physiology. However, modern buildings are often designed with no concern for natural light, and depend almost entirely on artificial light. There are instances on record of people leaving jobs because of the lack of natural light.