Lightbulb socket | Wikipedia audio article
A lightbulb socket, light socket, lamp socket, or lamp holder is a device that mechanically supports and provides electrical connections
for a compatible electric lamp. Sockets allow lamps to be safely and conveniently replaced
(re-lamping). There are many different standards for lamp holders, including early de facto
standards and later standards created by various standards bodies. Many of the later standards
conform to a general coding system in which a socket type is designated by a letter or
abbreviation followed by a number. The most common type of sockets for mains electricity
is Edison screws, used in continental Europe and North America, while bayonet mounts dominate
in the Commonwealth countries and the automotive industry. Fluorescent lamps typically require
a two-pin, unthreaded socket. Not all lamps require a socket. For example,
some miniature lamps have wire leads suitable for direct connection to screw terminals or
other wires, and some reflector lamps provide screw terminals for electrical connections. == History ==
Early experimental incandescent lamps employed wire leads which had to be connected to screw
terminals, but this was inconvenient for commercial use. The Edison organization used simple wooden
receptacles with internal copper strips for lamps on the commercial steamship SS Columbia,
the first ship to use electric light bulbs.
These sockets included key switches, but required
bulbs to be mounted upright. The Edison organization developed a screw-base
in 1880 which was initially made of wood but later made of plaster of Paris. Many competitive
designs of lamps and sockets appeared in the early era of incandescent lighting, which
often was incompatible with other designs. == Construction and materials ==
The construction of a lamp holder socket defines and limits its intended use. Ceramic insulation
can withstand considerably higher operating temperatures than bakelite or other plastics.
The electrical components and wires must be designed to carry the intended current plus
a safety factor. The contact surface area, thickness and conductivity
of the metal, connection methods, and maximum operating temperature must all be considered
in the design of a new socket. In addition, mechanical factors such as the shape of the socket,
fixture mounting and attachment, lamp support, ease of re-lamping, and total cost of manufacture
must be considered. Sockets designed for ordinary household and industrial use have much more
design leeway than those used in precision applications.
The lamp holder must be located far enough from the filament that the metals with the
the lowest melting point will remain solid.
Historically this metal was a tin/lead solder whose melting
point might be as low as 180 °C (360 °F). Due to the thermal changes from ambient temperature
to full operating temperature, the design of a socket must allow for a considerable
amount of expansion and contraction. Spring elements are required to accommodate these
dimensional changes. However, the temperature at which a metal loses its spring is far below
the melting point. This is why some older sockets that no longer work can be restored
by prying up the base spring slightly.
Lampholder failures are usually caused by
mechanical abuse or by overheating. A socket with a built-in switch is far more likely
to fail in normal use as the switch parts wear out. Insulation failures are usually
caused by impacts or by difficulty inserting or removing a lamp. Sockets used outdoors
or in damp areas often suffer from corrosion which can cause the lamp to “stick” in the
socket and attempts to change a lamp can result in the breakage of either the lamp or the lamp holder.
The corrosion is not only environmentally produced but may be a result of the current
flowing through the parts when there is appreciable resistance between the parts. Fixtures in
such environments may require gaskets or other waterproofing methods to prevent the buildup of
moisture in the socket area. == Edison screw bases == E10 Miniature (Flashlight lamp)
E11 Mini-Candelabra E12 Candelabra
E14 European E17 Intermediate
E26 Medium E27 Medium
E39 Mogul E40 Mogul
3-Way (modified medium or mogul socket with additional ring contact for 3-way lamps)
Skirted (PAR-38)The light bulb commonly used since the early 20th century for general-purpose
lighting applications, with a pear-like shape and an Edison screw base, is referred to as
an “A-series light bulb.” This most common general-purpose bulb type would be classed
as “A19/E26” or the metric version “A60/E27”.
== Bayonet styles == BA9s Miniature bayonet
BA15s Single Contact Bayonet BA15d Double Contact Bayonet
Bay15d Indexed DC Bayonet Bay22 Double Contact Bayonet
Bayonet Candelabra with prefocusing collar P28s Medium prefocus
P40s Mogul prefocus == Bi-post == With bi-post bases, lamp orientation is fixed
so filament will always be in the focal plane. Filament configurations such as the C13D (coiled,
zig-zagged) emit far more light perpendicular to the zig-zag than parallel to it. Mogul bi-post (G38) can handle up to 100 amps
and is used with searchlights and film & stage lighting fixtures of 1000 watts or larger.
Incandescent, halogen, and HMI light sources use this design.
Medium bi-post (G22) is used with film & stage lighting fixtures between 250 and 1000 watts.
Mini bi-post (G4-G6)Common types: G4 – 4 mm pin spacing
GU4 & GZ4 – are the same as G4 and only denote what lamp mount clip is needed to hold the
actual light bulb in place G5.3 – 5.3 mm pin spacing
GU5.3, GX5.3, GY5.3, GZ5.3 – are same as G5.3 and only denote what lamp mount clip is needed
to hold the actual light bulb in place G6.35 – 6.35 mm spacing
GY6.35 & GZ6.35 – are the same as G6.35 and only denote what lamp mount clip is needed to hold
the actual light bulb in place G8 – 8 mm pin spacing
GU8 – same as G8 and only denotes what lamp mount clip is needed to hold the actual light
bulb in place GY8.6 – 8.6 mm pin spacing
G9 – 9 mm pin spacing G12 – 12 mm pin spacing ==
Bi-pin connector == Medium bi-pin is used on each end of a T12
fluorescent lamp Mini bi-pin is used with MR16 halogen lampsThe
the two-pin socket is an update of the bi-post design with smaller pins designed to reduce
the cost of manufacture.
The 1000-watt FEL medium two-pin base halogen lamp allows designers
to insert the lamp into the end of the ellipsoidal reflector through a smaller hole than previously
possible with conventional incandescent lamps. This improves efficiency compared to the older
side-inserted lamp or a double-ended lamp which requires two holes. One variation is
the polarized two-pin socket – used primarily in projectors, which defines the exact positioning
of the filament on one side. This improves the “point source” characteristic necessary
for building complex optical systems.
Another facet of the two-pin design is that
many new designs of lamps use baseless glass envelopes. The wire leads are thickened and
crimped in the glass envelope of the lamp base. The MR16 is an example of this design;
the actual lamp is inserted into the reflector with the leads sticking out and a ceramic
paste is used to glue it in. ==
Wedge base == Miniature lamps may have a wedge base made
of glass or plastic. The base may be an extension of the glass envelope of the bulb, with the
wire leads of the lamp folded up at the base. Some wedge bases are made of plastic and slipped
over the wire leads. A wedge base holds the lamp by spring compression in the socket.
The lamp is inserted and removed without twisting.
Wedge base lamps are widely used in automotive
applications and many Christmas light strings use plastic wedge-based bulbs. == Fluorescent tubular lamp standards ==
Fluorescent Linear Tube Light bulbs are measured in ⅛s of inches. So a T12 fluorescent is
12 ⅛s of an inch in diameter or 12/8 = 1.50″ T4 – 4/8 or 0.500″ in diameter
T5 – 5/8 or 0.625″ in diameter T8 – 8/8 or 1.00″ in diameter
T10 – 10/8 or 1.25″ in diameter T12 – 12/8 or 1.50″ in diameter ===
Lamp base styles === Some of the above base styles are now obsolete.
The trend in recent years has been to design newer bases to reduce the waste of raw materials
and simplify the replacement process.
== Standards ==
The United States standards for lamp sockets are published by ANSI and developed by NEMA,
are generally harmonized with the relevant IEC standards, and include:
ANSI_IEC C78.81, American National Standard For Electric Lamps—Doublecapped Fluorescent
Lamps-Dimensional and Electrical Characteristics ANSI_IEC C81.61, Standard for Electrical Lamp
Bases – Specifications for Bases (Caps) for Electric Lamps.
ANSI_IEC C81.62, American National Standard for Electric Lampholders
ANSI standard number C81.64, titled Guidelines and General Information for Electric Lamp
Bases, Lampholders, and Gauges and outlines the dimensions and tolerances of standardized
lamp sockets.
ANSI_IEC C81.63, American National Standard
for Gauges for Electric Lamp Bases and Lampholders ANSI C81.64, American National Standard for
Guidelines and General Information for Electric Lamp Bases, Lampholders, and Gauges
IEC 60061-4, Lamp Caps and Holders Together with Gauges for Control of Interchangeability
and Safety Part 4: Guidelines and General Information.
