Lighting

Energy Consumption

Lighting is usually the second greatest consumer of energy after heating and cooling. Energy use ranges from 20 to 95 % of total energy use, depending on the size and type of building. It is about 50 % for single homes and 70 % for apartments. Large, high population buildings, such as schools, office buildings, supermarkets, and hotels/motels have the highest lighting energy use.

Lighting Types

There are three types of lights in use today: incandescent, fluorescent and light emitting diode (LED).

Incandescent

Incandescent lights, in all their many forms, have long been used for lighting in homes. Incandescent lights have a very low lighting efficiency (the ratio of light intensity to energy consumed, expressed as lumens per watt). Most household incandescent lights have lighting efficiencies of 8 to 21 lumens per watt. The low lighting efficiency is because most of the energy consumed goes to heat the filament to very high temperatures (~ 6,500 0C).

Fluorescent

Fluorescent bulbs work by passing electricity across electrodes. The bulbs contain a mixture of argon and mercury vapor. The electrons in the electrical current excite the mercury which then releases photons. The photons react with the phosphor coating the inside of the bulb to produce visible light. Fluorescent lights have an energy efficiency of about 50 to 100 lumens per watt. They produce less heat than incandescents.

Most fluorescent lights come in standard four-foot lengths and two inch diameters, and are mostly used for industrial lighting in a variety of combinations. Newer products have somewhat higher energy efficiencies and come in one inch diameters. Today fluorescent technology can be used to replace standard incandescent bulbs. These lights are called compact fluorescent lamps (CFL). They have higher energy efficiencies than fluorescents, have longer life, but are more expensive. A major drawback is their inability to produce “true” white light as well as incandescents.

LED

LEDs have been around since the 1960s, but have come into practical use as replacements for incandescents and fluorescents in this decade. LED have lower energy consumption than incandescents and fluorescents, and have longer lifetimes.

They produce almost no heat, and the color of their light can be manufactured to almost any specification. Lighting efficiencies have been reported at well over 100 lumens per watt, but DOE found operational efficiencies to be around 30 lumens per watt. LEDs are more expensive than incandescents and fluorescents, and require more precise current and light management. LEDs themselves are quite small (< 0.5 inch diameter) and are clustered together in various combinations together with optical components to determine the light pattern. They can be used in standard light sockets