A light bulb that produces a soft warm light by electrically heating a tungsten filament so that it glows. Because so much of the energy is lost as heat, these are highly inefficient sources of light. Included in this category are the familiar type of light bulbs which screw into sockets, as well as energy-efficient incandescent bulbs, such as Reflector or R-Lamps (accent and task lighting), Parabolic Aluminized Reflector (PAR) lamps (flood and spot lighting), and Ellipsoidal Reflector (ER) lamps (recessed lighting).
The "standard" type of light bulb, invented by Thomas Edison 100 years ago, in which electricity flows through a small filament which disperses a small fraction of its energy as light and over 90% as heat. They are very inefficient and should not be used in RE systems. (See Compact Fluorescent).