Light bulb

An incandescent light bulb with its glowing filament.

A light bulb is a sealed body of glass (a bulb or globe) encasing a source of illumination.

Invention of the incandescent bulb (1880's)

The first (and for decades, the only) type of light bulb was the incandescent lamp. Its globe contains two electrical points of contact, a filament (a coil made of tungsten that glows brightly when current is applied), and an amount of an inert gas. The invention of the incandescent light bulb is usually credited to Thomas Alva Edison, who filed for a patent dated January 27, 1880 (patent #223898(US)). However multiple inventors and scientists at the time were also working to produce an incandescent bulb. Englishman Sir Joseph Swan produced an electric bulb in 1878. In 1880, Edison and his engineering staff produced a bulb very similar to the one we have today, using a bamboo fiber filament lamp that lasted between 1200-1500 hours and was rated at 16 watts.

Types of light bulbs

Different types of light bulbs exist today as a result of lighting requirements and energy demands.

• Incandescent light bulbs consist of a wire filament (typically made of tungsten metal) that is heated by passing an electrical current through it. The filament is heated to a high enough temperature that it gives off visible light, much as an electrical heating element in a toaster or on an electric stove top glows when heated. Running the filament at a higher temperature will increase the efficiency of the bulb, as more power is then radiated as visible light and less power is radiated as wasteful, invisible infrared radiation. However, a bulb with a hotter filament will also not last as long, as the filament material will then more quickly evaporate away over time. Trading off efficiency vs. bulb lifetime is a consideration for designers and manufacturers of light bulbs when selecting an operating temperature for a filament.

• Halogen light bulbs also use a heated wire filament and are therefore also a type of incandescent bulb. They get their name from the addition of a halogen gas to the inside of the bulb. The halogen gas allows the filament to be run hotter, which increases the bulb's efficiency, without sacrificing bulb lifetime. A primary disadvantage is that the heat produced by a halogen bulb is much greater than that of an incandescent and has been the cause of some fires as a result. Halogen systems also require a special type of socket. Some halogen systems may require an integrated step-down transformer which doesn't necessarily decrease the amount of power consumed, but allows for adjustment to be made from a "dimmer system" in order to control the amount of light produced by each bulb.

• Fluorescent lights use a phosphor coating on the inner wall of the bulb, which is typically in the shape of a long narrow tube. The phosphor converts ultraviolet light, which is not visible, into visible light. The ultraviolet light is produced within the tube by passing an electric current through a gas that is comprised of mercury vapor. Since these lamps contain mercury, a toxic heavy metal, they should be recycled and not added to landfills.

• Compact Fluorescent Lights (CFLs) are smaller versions of fluorescent lights that are designed to fit into regular lamp sockets. The advantage of CFLs are that they produce mostly visible light but with very little power consumption. Like standard fluorescent lights, CFLs contain mercury, a toxic heavy metal, and should be recycled rather than added to landfills.

• LEDs, or Light Emitting Diodes, are small, compact sources of light usually integrated into electronics, although they have become more popular in consumer lighting because of the relatively low production cost, low energy demands, and high light output. The light can be either a single color that is directly emitted by the diode or, as with fluorescent lamps, emitted by a phosphor that converts the directly emitted light into white light.

• Gas discharge lamps heat a gas, rather than a solid wire filament, by passing an electrical current through the gas within the bulb. Their primary use is for outdoor lighting at night, for example along roadways or in outdoor sports stadiums. A discharge lamp is typically named for the type of gas used. Types of discharge lamps include neon, high-pressure sodium, low-pressure sodium, metal halide, and mercury vapor lamps.

U.S. transition to LED bulbs

In the United States, incandescent, halogen and compact flourescent light bulbs are banneed from being sold by the U.S. Department of Energy, effective as of August 1, 2023. Their manufacture was banned as of January 2023.

LED lights last twenty-five times longer than incandescent ones and require only a fraction of the energy. LED bulbs with a Kelvin rating of 2700 have a warm light akin to older incandescent bulbs. But many cheaper LED bulbs have a Kelvin rating of 5000+, which provides a garish blue-white light (more akin to daylight) that people may not enjoy, especially at night.

Households using mechanical dimmers with incandescent bulbs may also need to replace the dimmer with ones rated to work with LED bulbs.

Compact flourescent bulbs are included in the ban because of their toxic mercury that can be released into the home if broken and should not be placed in landfills upon disposal.

Conversion of tube flourescent bulbs to LED

In industrial settings, four-foot T12 flourescent tube light fixtures are very common. Although they are still legal, tube flourescent bulbs (as opposed to compact flourescent bulbs) have not been banned. However, converting them to LED is economically feasible despite the initial cost of buying LED replacement bulbs and the effort of converting fixtures. The fixtures of linear flourescent tube light bulbs, which require a ballast to modulate electrical current and to start, can be rewired to use no ballast and instead use LED tube-shaped bulbs at a fraction of operational cost, with bulbs lasting much longer. Elimination of the need for the ballast also makes them much more reliable, as ballasts were a typical point of failure resulting in flickering lights, a humming sound, or lights which would not turn on at all.

Gallery

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  An incandescent light bulb with its glowing filament.

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  A 23-watt compact flourescent lamp

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  The sockets of linear flourescent lamps (size T5, T8 and T12) can now be replaced by LED lamps with a slight change in fixture wiring to exclude the ballast.