Lightbulb socket

Light bulbs draw their power from wires via electrical/mechanical connections.

There are many different standards for these sockets, created by de facto and by various standards bodies.

Some types of socket are listed here.

"Decorative" and standard screw base (Edison screw) bulb bases

• Miniature E-11
• Candelabra E-12
• European E-14
• Intermediate E-17
• Medium E-26 (This is what Americans call a "normal" lightbulb)
• 3-Lite (modified mogul socket with additional ring contact for 3 way bulbs)
• Mogul E-40

Bayonet styles

• Miniature bayonet
• Bayonet candelabra
• Bayonet Candelabra with prefocusing collar
• Medium prefocus
• Mogul prefocus

Bi-Post

The Bi-post base has several advantages

• Bulb 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.
• Sockets

• Mogul Bi-post is used with searchlights, film & stage lighting fixtures 1000 watts or larger. Incandescent, halogen and HMI light sources use this design.
• Medium Bi-post is used with film & stage lighting fixtures between 250 and 1000 watts (the development of the T14 base up to horizon design for ellipsoidal spotlights was one of the most important innovations of the mid 20th century)
• Mini Bi-post

Bi Pin

• Medium bi-pin is used on each end of a T12 florescent bulb
• mini bi-pin is used with MR16 halogen bulbs

Two Pin

The 2 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 2 pin base halogen lamp allows designers to insert the bulb into the end of the ellipsoidal reflector through a smaller hole than previously possible with conventional incandescent bulbs. This improves efficiency compared to the older side inserted bulb or a double ended bulb which requires two holes. One variation is the Polarized 2 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.

fluorescent tube standards

• T-5 mini
• T-8 medium
• T-12 large

Specialty

• Medium
• Three Contact Medium 3C Med
• ...

Phillips Compact Fluorescent types

• G-23
• GX23
• GX32d-2
• GX32d-3
• ...

General Electric Compact Fluorescent types

• ...
• ...

SLI Compact Fluorescent types

• ...
• ...

Design and Use Terms

As light bulbs are designed to meet specific needs from general illumination to precision control of the light emitted, lightbulb sockets must be designed and chosen based on the needs of the application.

Large Lamp Base Styles

Abbreviation	Term
Cand	Candelabra
DC Bay	Double contact bayonet candelabra
DC Pf	Double contact prefocus candelabra
EMEP	Extended mogul end prong ferrule contact
F	Ferrule contact
Mc	minican
Med	Medium
Med Bp	Medium bipost
Med Pf	Medium Prefocus
Med Skt	Medium Skirted
Med 2P	Medium two pin
MEP	Mogul End Prong
Mog	Mogul
Mog Bp	Mogul bipost
Mog Pf	Mogul prefocus
MS	Miniature screw (with reference shoulder)
MSP	Medium side prong
G38 Bp	G38 mogul bipost
Rect RSC	rectangular recessed single contact
RM2P	Rim mount two pin
RSC	Recessed single contact
S	Metal sleeve
SC Bay	Single contact bayonet
SC Pf	Single contact prefocus
SFc 10-4	Sleeve with threaded pin
SFc 15, 5-6	Sleeve with threaded pin
ST	Screw terminal
TB2P	TruBeam two pin
Tf	Trufocus (also four pin)
TLMS	Tru-Loc miniature screw
2B	Two button
2PAG	Two pin all glass
2PAGC	Two pin all glass with ceramic cover
2PM	Two pin miniature
2PP	Two pin prefocus
3P	Three prong

Some of these base styles are obsolete and are included for reference. The trend in recent years has been to design newer bases to reduce waste of raw materials and make it easier to replace light bulbs.

Bulb Dimensions

Abbreviation	Term
LL	Light length (filament length)
LCL	Light center length (optical center of the filament)
C-to-C	Contact to contact
MOL	Maximum overall length
Dia	Diameter
Max	Maximum

If the socket design dimensions are known it is easy to calculate how high the LCL of the bulb will be above the base of the socket. The MOL of the bulb plus the seated height of the bottom of the base will help determine the size of a container for the finished lighting fixture.

Common Burn Positions

Abbreviation	Term
BD	Base down
BD/45	Within 45 degrees of vertical base down
BD/Hor	Base down to horizontal
BU	Base up
Horiz	Horizontal
Univ	Universal

Examples using conventional incandescent bulbs (all require ceramic high temperature sockets and wiring):

• A 1000 watt PS-52 (Pear Shaped - 52/8 = 6.5" maximum diameter) bulb is designed for universal base orientation. The long neck keeps the base cool enough in any position that solder on the base will not melt.
• A 500 watt G-40 (Globe - 40/8 = 5" maximum diameter) bulb is specified as BD/Hor in order to keep the base below the highest part of the bulb so solder on the base will not melt.
• A 750 watt T-12 (Tubular - 12/8 = 1.5" maximum diameter) bulb designed for BU use in ellipsoidal spotlights moves the filament to the lowest end of the glass bulb, creating the necessary distance to the base for cooling while having a small diameter so it can be inserted into an ellipsoidal reflector in such a way as to make the reflector more efficient.

Contemporary lightbulb construction for lower wattage (15 to 100watts) bulbs rarely uses solder to connect the bulb wire leads to the base. Instead the connection is spot welded. This allows the base to be made from aluminum rather than brass and keeps the cost down.

References

• http://www.goodmart.com/info/base_general.aspx
• http://www.lightbulbsdirect.com/page/001/CTGY/Base
• http://www.gelighting.com/na/business_lighting/education_resources/literature_library/catalogs/downloads/Lighting_and_Ballasts_Section_D_Appendix_and_Glossary.pdf
• IES Lighting Handbook Second Edition (1952) (Illuminating Engineering Society)
• 1990 Lampholders catalog from GTE Sylvania Emmissive Products