1stlinks incandescent light bulbs, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process returns metal to the filament, extending its life. The light bulb is supplied with electrical current by feed-through terminals or wires embedded in the glass. Most bulbs are used in a socket which supports the bulb mechanically and connects the current supply to the bulb's electrical terminals.
 
Incandescent bulbs are produced in a wide range of sizes, light output, and voltage ratings, from 1.5 volts to about 300 volts. They require no external regulating equipment, have low manufacturing costs, and work equally well on either alternating current or direct current. As a result, the incandescent lamp is widely used in household and commercial lighting, for portable lighting such as table lamps, car headlamps, and flashlights, and for decorative and advertising lighting.
 
Some applications of the incandescent bulb use the heat generated by the filament, such as incubators, brooding boxes for poultry, heat lights for reptile tanks, infrared heating for industrial heating and drying processes, and the Easy-Bake Oven toy. This waste heat increases the energy required by a building's air conditioning system.
 
Incandescent light bulbs are gradually being replaced in many applications by other types of electric lights, such as fluorescent lamps, compact fluorescent lamps, cold cathode fluorescent lamps (CFL), high-intensity discharge lamps, and light-emitting diodes (LEDs). These newer technologies improve the ratio of visible light to heat generation. Some jurisdictions, such as the European Union, are in the process of phasing out the use of incandescent light bulbs in favor of more energy-efficient lighting.1stlinks.
 
Efficiency and environmental impact
Xenon Halogen Lamp (105 W) with an E27 base, intended for direct replacement of a non-halogen bulb
 
Approximately 90% of the power consumed by an incandescent light bulb is emitted as heat, rather than as visible light.
 
The effectiveness of an electric lighting source is determined by two factors: the relative visibility of electromagnetic radiation, and the rate at which the source converts electric power into electromagnetic radiation.
 
Luminous efficacy of a light source is a ratio of the visible light energy emitted (the luminous flux) to the total power input to the lamp. Visible light is measured in lumens, a unit which is defined in part by the differing sensitivity of the human eye to different wavelengths of light. Not all wavelengths of visible electromagnetic energy are equally effective at stimulating the human eye; the luminous efficacy of radiant energy is a measure of how well the distribution of energy matches the perception of the eye. The maximum efficancy possible is 683 lm/W for monochromatic green light at 555 nanometres wavelength, the peak sensitivity of the human eye. For white light, the maximum luminous efficacy is around 240 lumens per watt, but the exact value is not unique because the human eye can perceive many different mixtures of visible light as "white".
 
The chart below lists values of overall luminous efficacy and efficiency for several types of general service, 120-volt, 1000-hour lifespan incandescent bulb, and several idealized light sources. A similar chart in the article on luminous efficacy compares a broader array of light sources to one another.
 
Due to the higher energy usage of incandescent light bulbs in comparison to more energy efficient alternatives, such as compact fluorescent lamps and LED lamps, many governments have introduced measures to ban their use, by setting minimum efficacy standards higher than can be achieved by general service lamps.
 
In the United States, federal law has scheduled the most common incandescent light bulbs to be phased out by 2014, to be replaced with more energy-efficient light bulbs. In Brazil, they have already been phased out between 2007 to 2010. Traditional incandescent light bulbs were phased out in Australia in November 2009.
 
However, there has been much resistance to these phasing out of incandescent lamps, owing to the low cost of incandescent bulbs, the instant availability of light, and possible ill health effects including the problems of mercury contamination with CFLs. Varying and unpredictable quality of current CFLs and LED lamps adds to the resistance
 
Construction
 
Incandescent light bulbs consist of a glass enclosure (the envelope, or bulb) with a filament of tungsten wire inside the bulb, through which an electric current is passed. Contact wires and a base with two (or more) conductors provide electrical connections to the filament. Incandescent light bulbs usually contain a stem or glass mount anchored to the bulb's base that allows the electrical contacts to run through the envelope without gas/air leaks. Small wires embedded in the stem in turn support the filament and/or its lead wires. The bulb is filled with an inert gas such as argon to reduce evaporation and prevent oxidation of the filament.
 
An electric current heats the filament to typically 2,000 to 3,300 K (3,140 to 5,480 °F)), well below tungsten's melting point of 3,695 K (6,191 °F). Filament temperatures depend on the filament type, shape, size, and amount of current drawn. The heated filament emits light that approximates a continuous spectrum. The useful part of the emitted energy is visible light, but most energy is given off as heat in the near-infrared wavelengths.
 
Three-way light bulbs have two filaments and three conducting contacts in their bases. The filaments share a common ground, and can be lit separately or together. Common wattages include 40;60;100,150, and with the first two numbers referring to the individual filaments, and the third giving the combined wattage.
 
While most light bulbs have clear or frosted glass, other kinds are also produced, including the various colours used for Christmas tree lights and other decorative lighting. Neodymium-containing glass is sometimes used to provide a more natural, daylight appearing light.

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