Incandescent lamps consist of a wire filament inside a glass bulb that is usually filled with inert gas, and they produce light when an electric current heats the filament to a high temperature. Incandescent lamps have a low efficacy (10-17 lumens per watt) compared with other lighting options—because most of the energy released is in the form of heat rather than light—and a short average operating life (750–2,500 hours).
The three most common types of incandescent lamps are:
- Standard incandescent (A-type) lamps
- Energy-saving incandescent (halogen) lamps
- Reflector lamps.