Understanding common household light bulb shapes, sizes, and styles is important whether you’re converting outdated incandescent fixtures into energy-efficient ones or using LED bulbs for new-construction applications. Every light bulb has identifying characteristics that are represented by a letter or series of letters and a number; these are known as light bulb codes. The letter or letters in a bulb code indicate either shape or special features such as reflector type. Numbers in a bulb code indicate size in millimeters or eighths of an inch. These codes will tell you if a bulb will fit in your fixture and if it’s the right shape.
For every light fixture or application, there’s going to be a specific bulb or light bulb shape that will fit best and provide the right type of light. If you understand bulb codes, it’s easy to look at a light fixture and know right away what kind of bulb you’ll need.
Let’s talk about light bulb groups, their bulb codes, and what applications those bulbs are typically used for.
Standard/arbitrary (A) bulbs are the most widely used and thought of when it comes to household lighting. These bulbs work well for a variety of applications, such as ceiling lights, lamps, vanity lights, kitchen lights, closet lights, porch light fixtures, and so many more.
Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
A15 bulb: 15/8 = 1-7/8″ diameter
A19 bulb: 19/8 = 2-3/8″ diameter
A21 bulb: 21/8 = 2-5/8″ diameter
A25 bulb: 25/8 = 3-1/8″ diameter
Most common base types:
Globe (G) bulbs have a full, round shape and are available in various sizes. They can be used for many applications throughout the home, such as foyer lights, kitchen lights, chandeliers, and ornamental fixtures. The most common type is the large G30 bulb, which is used in bathroom and makeup vanities.
Depending on the bulb, numbers in each code can refer to the bulb’s diameter in one-eighths of an inch or in millimeters.
G11 bulb: 11/8 = 1-3/8″ diameter
G14 bulb: 14/8 = 1-3/4″ diameter
G16/G50: 16/8 = 2″ diameter
G60: 60 millimeters = 2-3/8″ diameter
G25/G80: 80 millimeters = 3-9/64″ diameter
G30: 30/8 = 3-3/4″ diameter
Most common base types:
All of the bulbs in these groups resemble the shape of a candle flame and are often referred to as candle bulbs. Conical (C) bulbs are shaped like a cone. Conical angular (CA) bulbs are shaped like a cone but have a bent tip. Blunt-tip (B) bulbs are very similar to C-type bulbs but have more of a torpedo or bullet shape. These bulbs can be used in chandeliers, wall sconces, pendant lights, night lights, decorative light strands, holiday light strands, and other decorative home lighting applications.
Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
B10 bulb: 10/8 = 1-1/4″ diameter
CA10 bulb: 10/8 = 1-1/4″ diameter
C7 bulb: 7/8 = 7/8″ diameter
C9 bulb: 9/8 = 1-1/8″ diameter
C15 bulb: 15/8 = 1-7/8″ diameter
Most common base types:
BR stands for bulged reflector. Traditionally, the inside surface of an incandescent BR bulb is covered in reflector material that is used to gather and cast a wide beam of light away from the bulb. LED BR bulbs don’t require the reflector material. These bulbs can have a frosted, clear, or patterned dome-shaped lens that diffuses light and provides a gradual fade into nonilluminated areas. BR bulbs also produce less shadows when compared to PAR bulbs. They’re a bit longer than PAR bulbs and tend to protrude from light housings but are used in similar applications, such as track lights, recessed lights, display lights, or can lights.
BR20 bulbs are often referred to as R20 but have the same characteristics of other BR bulb types. The R stands for reflector.
Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
BR20/R20 bulb: 20/8 = 2-1/2″ diameter
BR30 bulb: 30/8 = 3-3/4″ diameter
BR40 bulb: 40/8 = 5″ diameter
Most common base type:
Multifaceted reflector (MR) bulbs are small in size with a reflective, faceted interior. The facets create a concentrated beam of light that can be displayed in a narrow spot or wide flood beam pattern. Because of the directional light they provide, MR LED bulbs don’t require the facets but often still have them. These bulbs are available in a variety of colors and can be used for many applications, including track lighting, recessed lighting, desk lights, and display case lighting. Many MR bulbs operate on low-voltage wiring systems, which makes them great for outdoor and landscape applications such as driveway lights, path lights, gazebo lights, paver lights, and malibu lights that have weatherproof housings.
Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
MR11 bulb: 11/8 = 1-3/8″ diameter
MR16 bulb: 16/8 = 2″ diameter
Most common base types:
Tubular (T) bulbs come in a variety of lengths and widths. Depending on their size, these bulbs can be used in applications ranging from chandeliers, wall sconces, and pendant lights to basement and garage troffer light fixtures.
Numbers in each code refer to the bulb’s diameter in one-eighths of an inch.
T7 bulb: 7/8 = 7/8″ diameter
T8 bulb: 8/8 = 1″ diameter
T10 bulb: 10/8 = 1-1/4″ diameter
T14 bulb: 14/8 = 1-3/4″ diameter
Most common base types:
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