Daylighting is the practice of placing windows or other openings and reflective surfaces so that during the day natural light provides effective internal lighting. Particular attention is given to daylighting while designing a building when the aim is to maximize visual comfort or to reduce energy use. Energy savings can be achieved either from the reduced use of artificial lighting or from passive solar heating or cooling. --Wikipedia

Great reading material on daylighting design and glazing selection: The Dumb's Architects Guide to Glazing Selection by Jason F. McLennan