The availability of electric lighting has changed the lives of people the world over, yet as a major user of electricity it has come under increasing scrutiny in recent years. This third edition of a bestseller restores some balance to the discussion by examining the ways in which people interact with lighting. These interactions influence the ability to perform visual tasks, the perception of people, objects and spaces, human comfort and behavior as well as human health and safety. It is only by understanding how to use light to achieve these ends, that lighting can be provided effectively and efficiently, to the benefit of all.