Editing Incandescent light bulb (section)

==Physical characteristics==
===Safety===
The filament in a tungsten light bulb is not easy to break when the bulb is cold, but filaments are more vulnerable when they are hot because the incandescent metal is less rigid. An impact on the outside of the bulb may cause the filament to break or experience a surge in [[electric current]] that causes part of it to melt or vaporize.
In most modern incandescent bulbs, part of the wire inside the bulb acts like a [[fuse (electrical)|fuse]]: if a broken filament produces an [[electrical short]] inside the bulb, the fusible section of wire will melt and cut the current off to prevent damage to the supply lines.

A hot glass bulb may fracture on contact with cold objects. When the glass envelope breaks, the bulb [[implosion (mechanical process)|implodes]], exposing the filament to ambient air. The air then usually destroys the hot filament through [[oxidation]].

===Bulb shapes ===
[[File:incandescent bulb shapes.svg|thumb|upright=2|Incandescent light bulbs come in a range of shapes and sizes.]]
Bulb shape and size designations are given in national standards.   
Some designations are one or more letters followed by one or more numbers, e.g. A55 or PAR38, where the letters identify the shape and the numbers some characteristic size.

National standards such as [[ANSI]] C79.1-2002, [[Indian Standard|IS]] 14897:2000<ref name="IS 14897:2000">{{cite web |title=IS 14897 (2000): Glass Bulb Designation System for Lamps — Guide |publisher=Bureau of Indian Standards |location=New Delhi |url=https://archive.org/details/gov.in.is.14897.2000 |access-date=3 July 2018 |pages=1, 4 }}</ref> and [[Japanese Industrial Standards|JIS]] C 7710:1988<ref name="JIS C 7710:1988">{{cite web |script-title=ja:JIS C 7710:1988 電球類ガラス管球の形式の表し方|url=http://kikakurui.com/c7/C7710-1988-01.html |access-date=21 March 2017 |language=ja |url-status=live |archive-url=https://web.archive.org/web/20161111224419/http://kikakurui.com/c7/C7710-1988-01.html |archive-date=11 November 2016}}</ref> cover a common terminology for bulb shapes.

{| class="wikitable"
|+ Examples
|-
! Description !! SI !! Inch !! Details
|-
| "Standard" lightbulb || A60 E26 || A19 E26 || [[⌀]]60&nbsp;mm (~⌀19/8&nbsp;in) [[A-series light bulb|A series bulb]], ⌀26&nbsp;mm [[Edison screw]]
|-
| Candle-flame bulb || CA35 E12 || CA11 E12 || ⌀35&nbsp;mm (~⌀11/8&nbsp;in) candle-flame shape, ⌀12&nbsp;mm Edison screw
|-
| Flood light || BR95 E26 || BR30 E26 || ⌀95&nbsp;mm (~⌀30/8&nbsp;in) flood light, ⌀26&nbsp;mm Edison screw
|-
| Halogen track-light bulb || MR50 GU5.3 || MR16 GU5.3 || ⌀50&nbsp;mm (~⌀16/8&nbsp;in) [[multifaceted reflector]], 5.33&nbsp;mm-spaced 12&nbsp;V [[bi-pin connector]]
|}

=== Common shape codes ===

;General Service/General Lighting Service (GLS)
:Light emitted in (nearly) all directions. Available either clear or frosted.
:Types: [[A-series light bulb|General]] (A), elliptical (E), mushroom (M), sign (S), tubular (T)
:120&nbsp;V sizes: A17, 19 and 21
:230&nbsp;V sizes: A55 and 60{{efn|name=EU-metric|1=Size measured in millimetres. See also [[A-series light bulb]].}}

;High Wattage General Service
:Lamps greater than 200 watts.
:Types: Pear-shaped (PS)

;Decorative
:lamps used in chandeliers, etc. Smaller candle-sized bulbs may use a smaller socket.
:Types: candle (B), twisted candle, bent-tip candle (CA & BA), flame (F), globe (G), lantern chimney (H), fancy round (P)
:230&nbsp;V sizes: P45, G95

;Reflector (R): Reflective coating inside the bulb directs light forward. Flood types (FL) spread light. Spot types (SP) concentrate the light. Reflector (R) bulbs put approximately double the amount of light (foot-candles) on the front central area as General Service (A) of same wattage.
:Types: Standard reflector (R), bulged reflector (BR), elliptical reflector (ER), crown-silvered
:120&nbsp;V sizes: R16, 20, 25 and 30
:230&nbsp;V sizes: R50, 63, 80 and 95{{efn|name=EU-metric}}

;Parabolic aluminized reflector (PAR)
:[[Parabolic aluminized reflector light|Parabolic aluminized reflector]] (PAR) bulbs control light more precisely. They produce about four times the concentrated light intensity of general service (A), and are used in recessed and track lighting. Weatherproof casings are available for outdoor spot and flood fixtures.
:120&nbsp;V sizes: PAR 16, 20, 30, 38, 56 and 64
:230&nbsp;V sizes: PAR 16, 20, 30, 38, 56 and 64
:Available in numerous spot and flood beam spreads. Like all light bulbs, the number represents the diameter of the bulb in {{frac|1|8}} of an inch. Therefore, a PAR 16 is {{cvt|2|in|order=flip}} in diameter, a PAR 20 is {{cvt|2.5|in|order=flip}} in diameter, PAR 30 is {{cvt|3.75|in|order=flip}} and a PAR 38 is {{cvt|4.75|in|order=flip}} in diameter.
[[File:GE 60 watt package light bulbs.jpg|thumb|A package of four 60-watt light bulbs]]

;Multifaceted reflector (MR)
:[[Multifaceted reflector]] bulbs are usually smaller in size and run at a lower voltage, often 12&nbsp;V.

[[File:MR-Variations.jpg|thumb|Left to right: MR16 with GU10 base, MR16 with GU5.3 base, MR11 with GU4 or GZ4 base]]

;HIR/IRC: "HIR" is a [[GE]] designation for a lamp with an infrared reflective coating. Since less heat escapes, the filament burns hotter and more efficiently.<ref>{{cite web |url=http://www.gelighting.com/na/business_lighting/education_resources/glossary.htm |title=Lighting Resources |work=GE Lighting North America |url-status=dead |archive-url=https://web.archive.org/web/20070703041351/http://www.gelighting.com/na/business_lighting/education_resources/glossary.htm |archive-date=3 July 2007 }}</ref> The [[Osram]] designation for a similar coating is "IRC".<ref>{{cite web |url=http://www.osram.com/osram_com/Tools_%26_Services/Calculators_and_Consultants/IRC_Saver_calculator/index.html |publisher=Osram |title=IRC Saver calculator |url-status=dead |archive-url=https://web.archive.org/web/20081223121730/http://www.osram.com/osram_com/Tools_%26_Services/Calculators_and_Consultants/IRC_Saver_calculator/index.html |archive-date=23 December 2008 }}</ref>

===Lamp bases===
{{Main|Lightbulb socket}}
[[File:Gloedelampe fatninger.jpg|right|thumb|40-watt light bulbs with standard E10, E14 and E27 Edison screw base]]
[[File:BCincandescentlamp.jpg|upright|thumb|The double-contact bayonet cap on an incandescent bulb]]

Large lamps may have a [[Edison screw|screw base]] or a [[Bayonet mount|bayonet base]], with one or more contacts on the base. The shell may serve as an electrical contact or only as a mechanical support. Bayonet base lamps are frequently used in [[Automotive lamp types|automotive lamps]] to resist loosening by vibration. Some tubular lamps have an electrical contact at either end. Miniature lamps may have a [[wedge base]] and wire contacts, and some automotive and special purpose lamps have screw terminals for connection to wires. Very small lamps may have the filament support wires extended through the base of the lamp for connections. A [[bipin]] base is often used for halogen or reflector lamps.<ref>{{cite web |title=Single-Ended Halogen Bases |url=http://www.bulbster.com/lightbulbs/singleended-halogen-c-783_43230.html |publisher=Bulbster.com |access-date=17 June 2013 |url-status=live |archive-url=https://web.archive.org/web/20130919152653/http://bulbster.com/lightbulbs/singleended-halogen-c-783_43230.html |archive-date=19 September 2013}}</ref>

In the late 19th century, manufacturers introduced a multitude of incompatible lamp bases. [[General Electric]]'s "[[Mazda (light bulb)|Mazda]]" standard base sizes were soon adopted across the US.

Lamp bases may be secured to the bulb with a cement, or by mechanical crimping to indentations molded into the glass bulb.

Lamps intended for use in optical systems have bases with alignment features so that the filament is positioned accurately within the optical system. A screw-base lamp may have a random orientation of the filament when the lamp is installed in the socket.

Contacts in the [[lightbulb socket]] allow the electric current to pass through the base to the filament. The socket provides electrical connections and mechanical support, and allows changing the lamp when it burns out.