Bulb Shapes & Sizes

A bulb is referred to by one or two letters (indicating the shape) followed by a number (indicating the diameter) in eights of an inch. The standard light bulb shape you first think of is an “A19 Bulb” shape. It is in the A family shape and it has a diameter of 19/8 inch, or 2 3/8”. The maximum overall length (MOL) is the length (in inches) of the bulb from one end to the other, tip to tip. Another common bulb is the BR30, a Bulge Reflector, which is 30/8 = 3 ¾” in diameter.

Common bulbs include:

A Standard household bulb
BR Bulge Reflector (replicate style of traditional halogen broad-beam bulbs)
C Night light, holiday string bulb or candelabra bulb
G Globe bulb (common in bathroom vanity lighting)
MR Multifaceted Reflector (common in track lighting)
PR Parabolic Reflector (spotlights and flood lights)
R Reflector

Some bulbs, such as ALR37mm and ALR56mm do not follow the rules. First they have 3 letters, not 2, and second, they use metric diameters.

Also, mini and globe holiday lights tend to be sold by the metric diameter, in millimeters. An M5 is a "mini" tube with a 5 mm diameter (about 1/5 of an inch.) A G12mm is a "globe" with a 12 mm diameter (just under 1/2 inch.) A G25mm is a "globe" with a 25mm diameter (about an inch.)

At EnvironmentalLights.com, the diameter is in eighths of an inch, unless it says mm, as in the ALR37mm example. Typically, the wattage goes in front of the bulb shape, so our 50PAR30L is a 50 Watt PAR 30 long neck.

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