What is an E39 socket?

E39 is the size of a light bulb base, E stands for Edison, which is a standard socket for light bulbs, and 39 indicates the diameter size of the bulb base. Diameter measurement is in millimeters not inches. E39 is also called the “Mogul” size and is primarily used in street lights and lamps that require a higher wattage such the ones found on parking garage canopy lighting,  the Metal Halide based wall packs, etc.

What is an EX39 socket?

The EX39 base has a longer tip base than EX39, it’s also called Mogul Extended base/socket.


What is the difference between E39 and EX39 socket?

There are 2 points of the difference.

  1. EX39 based bulbs can be used in fixtures with standard E39 or EX39 sockets. However, bulbs with E39 base will only operate in fixtures with an E39 socket but will not operate on EX39 base fixtures.
  2. Bulbs with EX39 bases have protective shields so can be used in either open or closed fixtures, however, E39 base bulbs can be used in enclosed fixtures only.

EX39 socket

E39 EX39 Socket


More information:

There are four commonly used thread size groups for mains supply lamps:

Candelabra: E12 North America, E11 in Europe/Asia
Intermediate: E17 North America, E14 in Europe/Asia
Medium or standard: E26 (MES) in North America, E27 in Europe/Asia
Mogul: E39/EX39 North America, E40  in Europe/Asia

E12 E14 E26 E39 EX39 E40 Sockets