Light Bulb Sizes :

​​A/C/R/MR/PAR/G/T/ What is The Difference

Whether you're changing the outdated incandescent fixtures or installing new bulbs in your residential or commercial building, understanding the different light bulb sizes is crucial.

Light bulbs have different distinctive characteristics that help us set them apart. The bulb sizes are identified by letters and numbers to indicate their features. In this article, we'll explain how to tell different types of light bulbs apart and the differences between their sizes, so keep reading to learn more about this topic.


How are Light Bulbs Named?

Each light bulb is named using a letter and a number. The letter refers to the shape of the bulb or a special feature like the reflector type in the bulb.

The number indicates the diameter of the bulb, which is measured in millimeters or eighths of an inch. The combination of a letter and a number indicates the size of the light bulb, so you can pick a bulb of an adequate shape and size.

Group A

Group A lights are extremely popular and can be used in several applications. It's what we know as the common household bulb, which you can use in a chandelier or a floor lamp.

These are the bulbs used in kitchens, closets, porches, and in ceilings. The number that comes after the letter refers to the diameter of the bulb.

Type of BulbSize
A151-7/8″ diameter
A192-3/8″ diameter
A212-5/8″ diameter
A253-1/8″ diameter


Group C


Group C light bulbs resemble the shape of a candle flame. These conical bulbs are shaped like a cone, adding a decorative element to your lighting fixture.

Group C bulbs have a bent tip, resembling the shape of a flame even more than the regular C type. These bulbs are usually used in chandeliers, wall lamps, and ornamental lamps. They also represent an excellent addition to decorative night lamps and home lighting applications.

The diameter or the number that comes after the letter refers to the diameter of the bulb in one-eighth of an inch.

Type of BulbSize
CA101-1/4″ diameter
C77/8″ diameter
C91-1/8″ diameter
C151-7/8″ diameter


Group R

Group R light bulbs are covered in a reflector material, which gathers the light and casts it away from the bulb's body. R light bulbs are usually used in recessed cans or as track lighting.

These bulbs are slightly longer and produce fewer shadows, so they can be used for various applications, especially where people spend most of their time as they're comfortable to use. The number refers to the diameter of the bulb.

Type of BulbSize
R121-1/2″ diameter
R141-3/4″ diameter
R162″ diameter
R202-1/2″ diameter


Group MR

MR bulbs or mirrored reflector bulbs are small in size, and the interior is faceted and covered in reflective material. This bulb concentrates the light beam to be displayed in a narrow and focused spot or a wide beam of light, depending on the design.

The MR bulbs are usually used in landscape lighting because they can replace halogen lights. They also come in various colors for decoration, so they can be used as desk lights, recessed lighting, and display lights.

Most MR bulbs operate in low-voltage wiring systems, so they work for outdoor applications like path lights, driveway lights, gazebo lights, and porch lights. They also usually have a waterproof casing to protect these bulbs from weather conditions.

Type of BulbSize
MR121-1/2″ diameter
MR141-3/4″ diameter
MR162″ diameter
MR202-1/2″ diameter


Group PAR

Group PAR bulbs are named after the Parabolic Aluminized Reflector. This is different from the U-shaped reflector that is used in incandescent bulbs.

The parabolic aluminized reflector is used to maximize brightness and direct the light to create a narrow or wide beam. The bulb has a shorter body and is usually installed by being flushed to the ceiling or other fixtures to reduce glare.


PAR bulbs are usually used for emergency outdoor lighting or spot lighting because the light from these bulbs doesn't fade as much as other types of bulbs. They also operate using low-voltage wiring, so they can be used in landscape lighting.


Type of BulbSize
PAR162″ diameter
PAR202-1/2″ diameter
PAR303-3/4″ diameter
PAR364-1/2″ diameter
PAR384-3/4″ diameter


Group G

Group G bulbs are commonly used in home applications. They're round-shaped and come in various sizes to suit various purposes.

You can use Group G bulbs as kitchen lights, foyer lights, or in chandeliers and ornamental fixtures. They can also be used as vanity lights or have a gold tint for a decorative effect. Although they come in different sizes, the most common bulbs are the bigger ones.

Type of BulbSize
G111-3/8″ diameter
G141-3/4″ diameter
G16 2″ diameter
G253-9/64″ diameter
G303-3/4″ diameter


Group T

Group T or tubular bulbs can be used in wall sconces, garage lights, in pendants, and as basement lighting. These lights come in various sizes, so you can pick the right one for your application.


Type of BulbSize
T77/8″ diameter
T81″ diameter
T101-1/4″ diameter
T141-3/4″ diameter
T162″ diameter


Light bulbs come in all shapes and sizes, and their shapes and sizes are indicated by a letter and a number. The letter indicates the shape of the bulb and affects how it can be used.

The number refers to the diameter of the bulb in eighths of an inch. Some types of light bulbs are interchangeable, but in most cases, every specific light bulb is suitable for a certain purpose.

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