Understanding common household light bulb shapes, sizes, and styles is important whether you’re converting outdated incandescent fixtures into energy-efficient ones or using LED bulbs for new-construction applications.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:

Diverse and impressive changes have been taking place in the lighting world this month. Read on to discover the fun and innovation!

In Lighting News…

Across the web, there was a consensus that LED holiday lights were the thing to have for the holidays. Not only are they energy-efficient, long lasting, and durable, they can also be interactive. We’ve seen families across the country creating Image via USA.Lighting.Philips.com

Other Cool Stuff…

In the last days of November, New York City residents were surprised by a light show atop the Empire State Building, synchronized to Alicia Keys’ “Empire State Of Mind.” The building’s new LED lighting system has over 16.7 million color possibilities, compared to the old system, which had only 10.

You probably know the iconic Pixar lamp – we usually see it hopping around before our movies start. Well, three students from Victoria University of Wellington have created a real-life replica of Luxo Jr., called Pinokio. With six servo motors, a webcam, some Arduino, and a bit of processing, the lamp came to life. Check out this video:

How about you? Any big lighting changes in your life this month? Please share!