It does matter what shape a light bulb is. The shape of the light bulb is important because it affects how the light is cast. Some bulb shapes provide more focused light while others give off a diffused glow in all directions. Plus, light bulb shape can impact the light fixture's design value. For instance, flame-shaped candle bulbs can work well in a chandelier.
Here's what you need to know about light bulb shape codes.
|BT||Bulged tube/chimney/blunt tip/bent tip|
01 of 08
An A designates the teardrop—or flower bulb—shape of a standard light bulb. This is where the name light bulb comes from. However, over time the name has become broadly used to describe any bulb shape.
Most standard screw-base light bulbs—such as the GE 60 watt incandescent light bulb—are A bulbs. A-19 and A-21 light bulbs, which are most 60 watt and 75 watt light bulbs respectively, are two common examples of A bulbs.
02 of 08
B can indicate one of three different shapes. When it is used by itself, it stands for bullet. A bullet light bulb is a cylinder with a smaller rounded end and a base that tapers in.
BR denotes a bulged reflector bulb. BR bulbs typically have two funnel-shaped reflector areas, one behind the other, to help shape and focus the light. They're narrow at the bottom and then flair out for a wider top.
A BT code can indicate a bulged tube or chimney light bulb—essentially just wide tubes sometimes with an even wider middle. It can also stand for a blunt tip light bulb—the ones that are flame-shaped with a rounded end. In addition, BT light bulbs can stand for bent tip, which is the exact opposite of a blunt tip. To minimize the confusion, many companies just spell out blunt tip or bent tip on the package rather than relying on the code.
03 of 08
A C stands for candle. These are the flame-shaped bulbs with the pointed, bent tips. Some companies have started using CA to designate their candle bulbs. That might have started as an attempt to distinguish candle flame-shaped bulbs from circline lamps.
CIR tells you it's a circular or circline lamp. In other words, it's a fluorescent tube made in a circle.
04 of 08
G is the code for a globular light bulb. These bulbs are often mounted in the open, so they can be seen. One popular location for globular light bulbs is in a multi-socket light fixture above a vanity mirror.Continue to 5 of 8 below.
05 of 08
An S bulb is made for use in a sign or appliance. These are not used in residential lighting.
06 of 08
A T stands for tube or tubular. This is the shape of, and the designation for, a standard straight fluorescent light bulb.
T-12 and T-8 fluorescent tubes are two fairly common examples of bulbs in this shape. Another is the T-10 tubular incandescent light bulb that is commonly used in the gallery light fixtures that mount to a picture's frame.
07 of 08
An R lamp is a reflector lamp. If you have any recessed lights or track lights in your home, you probably have some of these lamps installed.
Variations on the R shape include BR—bulged reflector bulbs, PAR bulbs—which have a parabolic shape, and MR—mirrored reflector bulbs.
08 of 08
The numbers that follow the letter codes denote the size of the light bulbs. They show the diameter of a bulb in eights of an inch.
Two familiar examples are T-12 and T-8 fluorescent tubes. The older T-12 tubes are 1 1/2 inches in diameter while the newer T-8 tubes are 1 inch in diameter. A common A-19 light bulb is 2 3/8 inches in diameter, and an R-30 flood light is 3 3/4 inches across its widest part.