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08/22/2014
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Bulb Bases

Posted on June 24, 2012 Category: Lighting Terms

Making the decision to switch to LEDs is the easy part, choosing your replacement bulb may not be. The first thing to determine is what type of base you need to fit into the socket.

The Standard “Medium” base is an E26. E stands for Edison and the number is the diameter in millimeters. Chandeliers and sconces typically accept E12 (Candelabra) base bulbs.

Bayonet (push-twist) bases fit into sockets with spring-loaded base plates (B or BA).

Halogen bulbs frequently have bases marked G, GU or GY, followed by a number. The second letter, if present, indicates the thickness of the pins (GU5.3 is 5.3 millimeters from pin center to pin center). The number is the center-to-center distance between the pins. The typical landscape bulb in your Malibu light is probably a GU5.3, which has 5.3 millimeters from pin center to pin center. We've noticed that many GU5.3 sockets designed for MR16 bulbs will also accept MR11 bulbs with GU4 pins. The pin "holes" are actually slots that accept a range of pin spreads from 4 to 5.3 mm.