Once you know the shape of the LED bulb you're looking to replace the next area of focus is identifying the base or socket. This is very important since buying a bulb with the wrong base will mean that it won't fit in the lamp or fixture. LED light bulb bases fall into three main categories.
Edison bases LED bulbs are the most popular especially when looking to replace household light bulbs. The different Edison bases are labelled with an E followed by a number that indicates the width of the base in millimeters. There are names given to several of these bases:
E12 = Candelabra base
E14 = Small Edison Screw base
E17 = Intermediate base
E26 = Medium base
E39 = Mogul base
Bi-pin bases are denoted with a G followed by a number which indicates the width of the space between the pins. Some of the most popular bi-pin bases are GU5.3 and GU10 which are found with MR16 LED bulbs. The GU5.3 bi-pin base just plugs into the socket while GU10, as well as GU24 base LED bulbs twist and lock into place. There are also instances when there are letter which follow the number to indicate how many pins the bulbs has where s stands for single-pin, d stands for double-pin, t for triple and q for quadruple.
Bayonet base LED bulbs have notches on the side of the base which are used to lock the bulb into place. There are generally two different kinds of bayonet base bulbs, single contact (SC) or double contact (DC). The contact type denotes if there is one or two contact points on the end of the bulb for electrical connectivity.
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1) Bulb Shape
2) Types of Bulb Bases