Energy In Buildings:
Lighting and Other Uses

Primary energy includes power derived from steam, oil, natural gas, and coal in addition to electricity.  Environmental conditioning (space heating and cooling) represents the largest energy load in most buildings. It is interesting that boosting the efficacy of lamps can help save some of this energy. Most lamps waste energy by generating heat. If lighting efficiency increases, less heat is generated easing the load on air conditioning units. 

To read the chart above, a definition is needed. A common measurement of energy is the British Thermal Unit or BTU. A BTU is the quantity of heat needed to raise the temperature of one pound of water one degree Fahrenheit. "Quad" in the chart stands for one quadrillion BTUs, and is a measure often used in energy industries.

Chart by Lee R. Anderson, compiled from information in "DOE Core Databook," 7 June 1996, U.S. Department of Energy.