We use the word Building to denote a structure, designed and built for the use and/or benefit of people. This is important to keep in mind, because we are not after saving energy at the expense of the beneficial use of a building space. If the space needs to be well-lit, it will remain well-lit after our energy management efforts. It is important to understand and appreciate the purpose of the building, or the space in the building. Another aspect of the building is that it does not exist as an independent entity. Buildings exist in connection with utility grids, pipelines, roads, sidewalks, landscapes, water supply and sewer infrastructure, and with other buildings and structures. We can think of buildings as being part of a built environment.