Incandescent lamps are thermal radiators: they generate light by heating tungsten wire. When an electric current is applied to the tungsten wire coiled to form a (single or coiled coil) filament inside an incandescent lamp, the tungsten glows. The filament is enclosed in a glass bulb which is either under vacuum or filled with nitrogen or an inert gas.

Incandescent lamps come a variety of designs with different bulbs (clear, crystal, matt, coloured) with light-reflecting coatings. They all emit a warm-white light and have very good colour rendering properties (R_a = 100). All incandescent lamps are dimmable.

2009 marks the 130th birthday of the incandescent lamp. In 1879, the American inventor Thomas Alva Edison optimised an invention that had been successfully demonstrated in 1854 by Johann Heinrich Goebel (Germany). The incandescent lamp is the oldest electric light source of all – and has been put into service millions of times over. It is equally widely used with an E27 (large) or E14 (small) screw base.

The days of the incandescent lamp are numbered

Incandescent lamps convert only around five percent of the energy they consume into light; the rest is radiated as heat. In view of this low luminous efficacy, Australia (2007) and New Zealand (2008) decided to ban incandescent lamps as of 2009/10.

Incandescent lamps will also be phased out in the EU by 2012 because of their poor energy balance. The rules for their removal from the market in stages are set out in Commission Regulation 244/2009 "Ecodesign requirements for non-directional household lamps", which enters into force on 13 April 2009. All non-clear (frosted) incandescent lamps and all clear incandescent lamps with a power rating of 100 W or more will disappear from the market in September 2009, all 75 W and higher models will follow in 2010, 60 W and higher in 2011 and lamps with a rating lower than 60 W in 2012. Special lamps for ovens, refrigerators, etc. are exempted from these rules.

Incandenscent lamps with reflector are not yet affected by these regulations.

The incandescent lamp's ecobalance is made even poorer by the fact that its life, at a maximum of 1,000 hours, is very short.