More than 4 billion incandescent light bulbs are in use in the United States. The basic technology in these bulbs has not changed substantially in the past 125 years, despite the fact that they convert less than 10% of their energy input into light. Improving light bulb performance can reduce overall U.S. energy use. About 20% of electricity consumed in the United States is used for lighting homes, offices, stores, factories, and outdoor spaces. Lighting represents about 14% of residential electricity use. This book provides an overview of lighting industry trends, with a focus on the life-cycle and energy consumption of incandescent, compact fluorescent and LED lamps.