Light Bulb Bases and Bulb Socket Types

By will_owen on 12/15/2017

Globe shaped bulb

It's time for you to replace or get a new light bulb for your light fixture. It should be pretty simple! All you have to do is get the same type of bulb that you previously had. But what happens when you go to the store to find that there are dozens of different types of bulbs? Don’t panic you are going to find all of the answers to all of your questions including: How do I know what bulb type I should get and why should the base type matter?

Which Bulb Base Do I Need?

Bulb Base:
4 pin T94 pin T9 base
  • Has 4 pins
  • Generally used with T9 circular light bulbs
  • Ceiling fans
  • Ceiling fixtures
  • 'BA' stands for bayonet base
  • 'd' means that it has double or two points of contact on the bottom
  • The number following 'BA' means that it has a 15 millimeter wide base
  • Replacing lighting for automobiles. Most commonly for their headlights
  • Lighting for school buses
  • 'BA' stand for bayonet base
  • 's' refers to its single point of contact
  • The number following 'BA' means that it's 15 millimeters in diameter
  • Replacing lighting for automobiles. Most commonly for their headlights
  • Candelabra Base
  • Usually supports a blunt tipped, flame tipped, or globe shaped light fixture
  • E-11 and E-14 candelabra bases are not interchangeable with this base
  • The 'E' stands for Edison
  • Diameter of 12 millimeters
  • Screws into a light socket
  • Chandeliers
  • Wall sconces
  • Some bath bars
  • Also known as the intermediate Edison screw
  • The 'E' stands for Edison
  • A base between a candelabra and medium base
  • 17 millimeters in diameter
  • Screws into a light socket
  • Inidcators for toys and holiday decorations
  • Exit Signs
  • Occasionally used in ceiling fans and other appliances
  • A medium base
  • Most common type of base in the US
  • Can be used with many different shaped bulbs
  • Standard for the household
  • 'E' stands for Edison
  • Has a 26 millimeter diameter
  • Screws into a light socket
  • Table lamps 
  • Most light fixtures around the house
  • Desk lamps
  • Also known as the mogul base
  • Rarely used except for commercial lighting
  • 'E' stands for Edison
  • A diameter of 39 millimeters
  • It's so large in order to handle the heat of a 300 watt bulb
  • Screws intop a light socket
  • A bi pin connector
  • Can be used with CFL or LED lamps
  • Has a twist lock design
  • Interchangeable between manufacturers with standard GU24 bulbs
  • Household lighting
  • Construction lights
  • A replacement for GU-110 halogen bases
  • Has 2 pins that are 10 millimeters apart
  • Operates at the same voltage as GU-110 so you won't have a problem with the transformer.
  • Twist and locky type base
  • Bath bars
  • Ceiling fans
  • Track lighting
  • MR-16 lamp base
  • With an electronic transformer you are going to have to purchase an LED MR-16 to confirm proper functionality
  • Track lighting heads
  • Bath bars
  • Ceiling fans
  • The pins diameter and spacing are the same as G4, 4 millimeters
  • Usually has a pair of grooves on the sides for a clip to hold the lamp
  • Mostly used in industry and commerce
  • Compatible with 2 and 4 pin G24d, GX24d, G24q or GGX24q base sockets
  • Usually used in ceiling reflectors
  • Industry lighting
  • Commerce lighting
  • Ceiling reflectors
  • A medium bi pin base
  • 13 millimeters between the two pins
  • Used for most of the T8, T10, and T12 linear fluorescent bulbs
  • Warehouses
  • Gyms 
  • Garages
  • Factories
G4 G4 bulb base
  • A bi pin base
  • 4 millimeters between the two pins 
  • Halogen version releases a lot of heat and can use only 20 watts
  • Under cabinet lighting 
  • Decorative lighting
  • Task lighting
  • RV/camper
  • Landscape lighting
G24Q G24Q bulb base
  • Has 4 pins
  • 24 refers to the millimeters between the pins
  • 'Q' means quad or that there are 4 bulbs
  • There are G24Q1, G24Q2, G24Q3
  • G24Q1 is usually used for 10 and 13 watt bulbs
  • G24Q2 are used with 18 watt bulbs
  • G24Q3 can use 26 watt bulbs
  • A common type base for fluorescent tubes
  • Usually used in LED linear high bays
  • Bi pin refers to the two pins located on the base
  • Warehouses
  • Gyms 
  • Garages
  • Factories

different bulb bases

The base of the light bulb is important because it determines what type of light fixture the bulb can be connected to. A lot of the common bulbs will have a screw or Edison base. This type of base is easy to use as it is to install. But if you were going to try to install a pin based light bulb that was designed for a screw base you won’t be able to connect them. In addition, just like the type of bulb you use, the base can help you determine what they can best be used for. An A19, for example, would be perfect for the office or home but would not do so well when you are trying to light a larger space like a warehouse. So knowing what the base and type of a bulb can help you get the type of lighting that you want.

Which Light Bulb Do I Need?

Bulb Type:
2G11 2G11 bulb type
  • Has four pins that are linear across the bottom of the base
  • External ballast gives you flexibility in application
  • If incorrectly installed the life of the bulb will be shortened
  • Hotels
  • Restaurant
  • Retail stores
  • Warehouse
  • Offices
A19 and A21 A19 bulb type
  • Also known as general service bulbs
  • 'A' is for the way that it's shaped like an 'A'
  • The number is the diameter of the bulb in millimeters
  • Directional light bulbs
  • Has a 180 degree beam angle so no light is wasted
  • Recessed lighting
  • Table lamps
B10                                                      B10 bulb type
  • The 'B' stand for blunt rather than flame tip
  • Can be used with a candelabra or medium base
  • Chandeliers
  • Decorative lighting
  • 'BR' stands for Bulge Reflector 
  • The number following 'BR' refers to the size of the bulb in 1/8 inches 20/8, 30/8, and 40/8 inches
  • Has a reflective coating found inside the bulb
  • BR40 is used for high ceiling and has higher wattages
  • BR30 bulbs are great for low ceilings
  • Ambient lighting
  • Hallways
  • Office space
CFL                                                      CFL bulb type
  • Also known as a compact fluorescent light
  • Made to replace incandescent bulbs
  • Contains mercury making it difficult to dispose of
  • Household lighting
  • Office 
  • Kitchen
C7                                                          C7 bulb type
  • Has a candelabra or E12 base
  • TYpically used in decorative lighting
  • Decorative lighting
  • Chandeliers
G25                                                      G25 bulb type
  • 'G' refers to the round globe shape 
  • The diameter of the bulb is 1/8 of an inch relative to the number following (ex: 25/8 = 3 1/8 inches)
  • Decorative lighting
  • Bathrooms
  • Theatres
  • Restaurants
  • Hotels
G30,G40,G50                                          G30 bulb base
  • 'G' means that the shape of the bulb is like a globe
  • THe number following 'G' is the diameter of the bulb in millimeters 
  • The base is usually a C7
  • Commonly used as string lights
  • Event decorating
  • Weddings
  • Patios
  • Cafes
  • Bistros
  • Clubs
Integrated LED                                      Integrated LED bulb
  • Outdoor light fixture
  • Simplifies lighting installation
  • Maintenance and lighting improvement can be difficult
  • Any outdoor light fixutres
JC                                                           JC bulb type
  • Low voltage halogen bulb
  • Capsul shaped
  • 2 pins at the base
  • Bulb can be damaged by oils from the skin and should not be touched bare handed
  • Under counter
  • Desk lamps
  • Accent lighting
LED Track Lights                                       LED track light bulb
  • Is a versatile light
  • Used on a continuous track device which has electrical conductors
  • Directional lighting
  • Spot lighting
MR16                                                   MR16 bulb type
  • 'MR' stand for mirrored reflector
  • The number that follow refers to the diameter that is 16/8 inches or 2 inches 
  • Has two pins on the bottom
  • Is a push fit type of bulb due to its installation
  • Track lighting
  • Display lighting
MR11                                                     MR11 bulb type
  • Has two sharp pins on the bottom
  • Classified as a push fit bulb by its form of installation
  • 12 volt lamp that requires a transformer
  • The width of the bulb is 35 millimeters
  • Bathrooms
  • Emergency lighting
  • Corridor lighting
PL                                                        PL bulb type
  • Made for retrofitting CFL plugins
  • Allow horizontal or vertical mounting
  • Generally used in commercial buildings
  • Downlights
  • Porch sconces
  • Decorative lighting
PAR                                                      PAR bulb type
  • 'PAR' stands for parabolic aluminum reflector
  • Has a sharp focused light
  • Durable and strong light outputs
  • Locomotive headlamps
  • Aircraft landing lights
  • Recessed lighting
R20                                                        R20 bulb type
  • 'R' stands for reflector
  • The number is the diameter of the lamp in terms of 1/8 of an inch (ex: 20/8 = 2.5 inches)
  • Track rings
  • Reccessed can
  • Indoor spotlight
  • Outdoor spotlight
  • Flood fixtures
S14, ST18, ST19                                           S14 bulb type
  • Comes in different colors
  • Vintage type of lighting
  • 'S' stand for straight side
  • The number refers to 1/8 of an inch of the bulbs diameter (ex: 14/8 = 1 3/4 inches)
  • Amusement parks
  • Hotels
  • Casinos
  • Theatrical lighting
T12                                                         T12 bulb type
  • 'T' means tubular shaped
  • The number refers to 1/8 of an inch of the bulbs diameter (ex: 12/8 = 1.5 inches)
  • Household lighting
  • Office area
  • Kitchens
T10                                                      T10 bulb type
  • 'T' refers to its tubular shape
  • The number that follows 'T' is the 1/8 of an inch for the lamps diameter (ex: 10/8 = 1 1/4 inches)
  • Banker lamps
  • Podium lights
T8                                                        T8 bulb type
  • 'T' refers to the tubular shape of the bulb
  • The number following 'T' refers to the diameter of the bulb which is 1/8 inches (ex: 8/8 = 1 inch)
  • More efficient in climate controlled areas
  • It won't shine as well with ceilings higher than 8 feet
  • Garages 
  • Storage areas
  • Fabrication floors
T5                                                           T5 bulb type
  • Designed to replace linear fluorescent tubes
  • 'T' means that it has a tubular shape
  • The number following refers to the diameter that is 1/8 of an inch (ex: 5/8 = 5/8 inches)
  • Linear fixtures 
  • Strip lights
  • Shop lights
  • Troffers
  • Under cabinet lighting
U Tube                                                   U Tube bulb type
  • A 'U' shaped bulb
  • Produces light the same way as a T5 and T8 through electronic circuits
  • House lighting
  • Offices
  • Kitchens

different bulb types




The type of light bulb that you choose can greatly affect the ambience and the beam angle of your setting. Depending on the type of setting that you are working with you may want a type of ambience that promotes production or one that makes people feel comfortable when they are there. Make your next trip to the electrical supply store easy and quick. Do you know what type of bulb and base you want? We are sure you do now!



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