Light Bulb Shapes Guide

If you’ve ever gone shopping for light bulbs, you’ve likely come across a wide range of letters and numbers. While these may seem confusing at first, it is actually surprisingly easy to read bulb shapes and sizes. The letter indicates the shape of the bulb, while the number shows the diameter of the bulb in eighths of an inch. However, you still need to understand which letter corresponds with each shape, as well as some of the different sizes at your disposal. So, in today’s guide, we will take a closer look at all of the most common light bulb shapes and sizes!

A Type Light Bulbs

A Type (or Type A) bulbs refer to the standard, pear-shaped bulbs. Some of the most common sizes include A19 and A15. The former is used in the majority of residential lamps and traditional light fixtures, while the latter is more commonly used for household appliances.

PS Type Bulbs

Like Type A bulbs, PS Type bulbs are pear-shaped, but with a thinner, elongated stem. However, PS Type bulbs have far fewer options in terms of size. In fact, you can often find just two different versions of the PS Type: PS25 and PS35.

B Type Light Bulbs

Type B bulbs are often known as candelabra bulbs. They have a thin stem and a point on top, with a middle section that curves outward. This gives them the appearance of a candle flame when turned on. For this reason, B Type bulbs are often used for electric candles and chandeliers.

C Type Light Bulbs

Like B Type bulbs, C Type (Conical) Bulbs have a wider middle and a point on top. However, Type C bulbs have greater variations in their shapes, with some versions having a very thin, elongated point, and others having a more rounded top. Either way, Type C bulbs are also great options for electric candles and holiday lights.

CA Type Bulbs

CA Type (Canonical Angular) bulbs have the same general shape as Type C, with the difference that the point is purposefully off-center. The cone shape combined with a bent tip means these bulbs mimic the look of a candle flame even better than Type B or C bulbs. Consequently, they are almost exclusively used for candles, candelabras, and chandeliers.

F Type Bulbs

F Type bulbs are yet another variation of the “candlelight” design. However, Type F bulbs tend to have a more bulbous base and a rounded tip, as well as indentations to make the bulb have a less polished, more natural look. This makes F Type a more versatile option that can work in a wide range of light fixtures.

PRISM Type Bulbs

As the name implies, PRISM Type bulbs are more angular in nature. They still maintain the cone shape of similar C Type bulbs, but they utilize more jagged edges (as opposed to rounded ones). This creates an interesting spectrum of light and colors when the bulb is turned on.

CFL Bulbs

CFL bulbs refer to both the type and shape of the bulb. CFL stands for “Compact Fluorescent Lamp” and all CFL bulbs have a tube that winds upward from the base in a circular shape. These bulbs are known for being more energy-efficient than standard incandescent bulbs (though less energy-efficient than LED bulbs). CFL bulbs, sometimes known as “coils,” usually come in three sizes: T2 Coil, T3 Coil, and T4 Coil.

U Shaped Bulbs

U Shaped bulbs refer to fluorescent bulbs with tubing that forms a “U” shape. These are often much larger bulbs that have specific uses in commercial or industrial settings. That said, they can be applied in residential homes as well.

Twin Tube

The Twin Tube is the standard U Shaped bulb, with one tube that wraps around into a U shape and connects to the base of the bulb. These bulbs can be of varying sizes, from long and thin to short and fat. In any case, Twin Tube light bulbs usually use 2 or 4-pin connectors. Sometimes, you can get a “double” Twin Tube that features two identical U Shaped bulbs on the same base.

Triple Tube

The Triple Tube features a connector base with three identical U Shaped tubes. The arrangement of the tube varies based on the size and style of the bulb. In most cases, the bulbs are arranged in a triangular shape.

Quad Tube

The Quad Tube features 4 identical U Shaped bulbs on one connector base. Like the Triple Tube, the arrangement of the bulbs can vary. Some feature an elongated base so that the bulbs can be placed all in one row, while others are arranged in a square to be more compact.

S Type Light Bulbs

S Type bulbs are short and round in shape. However, their bases generally adhere to the same sizes as Type A and B bulbs. These bulbs can vary in diameter from S6 all the way to S14.

G Type Light Bulbs

Type G bulbs are often known as “globe lights” because they are almost perfectly round. These bulbs also tend to come in higher wattages and produce bright light, making them a great option for bathrooms, mirrors, and vanities. G Type bulbs can range all the way from G9 to G40 in diameter.

R Type Light Bulbs

The R Type (Reflector) bulb has a mostly flat top and a built-in surface to reflect light to maximize light emission in a given direction. These bulbs are often used for highly specific purposes in commercial settings. However, they can also be used for displays or special areas in the home. They generally range in size from R12 to R40.

Q Type Light Bulbs

Type Q bulbs are one of the few letter-indicated bulbs that do not refer to the shape of the bulb. Instead, Q Type bulbs refer to bulbs that have a quartz glass shell. Q Type light bulbs can come in various shapes, designs, and sizes, though they are generally halogen bulbs.

PAR Bulbs

PAR stands for “parabolic aluminized reflector.” Like R Type bulbs, PAR bulbs generally have a flat top and a built-in reflector to direct light. However, PAR bulbs often have a softer light and a bowl-shaped stem.

MR Bulbs

MR Type (Multifaceted Reflector) bulbs are very similar to PAR bulbs. Both bulb types feature a flat top and a rounded bowl bottom. They can be used in projectors, as well as more standard residential and commercial light fixtures.

AR Bulbs

AR (Aluminum-Facetted Reflector) bulbs are a variation of the PAR and MR bulbs. They also feature a mostly flat (slightly rounded) top and a bowl-shaped bottom. These are specifically designed to create strong, direct beams of light.

BR Bulbs

BR (Bulged Reflector) is yet another variation of the PAR bulb. The BR bulb has a raised top with rounded edges. This is part of the “bulging” reflector, creating a softer light that extends to a larger area (as opposed to the more focused AR and MR bulbs).

T Type Light Bulbs

Type T bulbs are tube-shaped. This means that they feature longer (or taller) designs with smaller widths. There are various T Type bulb designs based on the size and style needed for a given fixture.

Linear Fluorescent Bulbs

A Linear Fluorescent Bulb refers to bulbs like the U Shaped Twin Bulb and similar designs. Essentially, it includes all fluorescent bulbs that are composed of just one tube. The tube can be curved or straight.

Linestra Bulb

The Linestra bulb is one of the more unique bulb shapes. It typically only comes in one size (T10) and has two connectors. It is long and thin, making it ideal for the tops of vanities or mirrors.

Wedge Bulbs

Wedge Bulbs refer to the shape and design of the bulb base. With a Wedge bulb, you have a connector that can be used as a base for small bulbs. This typically involves two wires that extend into the bulb itself. Wedge bulbs are always small and tend to be tube-shaped.

Rigid Loop Bulbs

A Rigid Loop bulb is a long bulb with looped connectors on each end. It tends to be round in the middle, though some have a flatter bulb shape. The Rigid Loop refers to the connectors that form a complete loop from one end of the bulb to the other.

Festoon Bulbs

Festoon bulbs are typically small, rectangular bulbs with double-ended connectors. Due to their small size, Festoon bulbs are frequently used on strings or in large quantities to create beautiful displays. In any case, Festoon bulbs are immediately recognizable for their two pointed, metallic end connectors.

BT Bulbs

BT bulbs are a less common shape that you may not see as often as other bulbs. These bulbs feature medium-width bases, enlarged middle sections, and medium-width tips. Though they are frequently associated with halogen bulbs, you can get LED and incandescent BT bulbs as well.

E Type Light Bulbs

Type E light bulbs refer to bulbs with a screw-in base. This delineation has little to do with the bulb itself. Therefore, you can have an E Type bulb that is also an F Type, a B Type bulb, or virtually any other bulb shape.

ED Type Bulbs

ED Type bulbs tend to be taller than standard bulbs and expand outward closer to the peak. They often feature more rectangular bases as well. Consequently, ED Type bulbs may not always fit into your standard home light fixtures.

We hope you found this guide on light bulb shapes both fun and informative! Are you interested in learning more about light bulb shapes and sizes? Are you ready to purchase high-quality light bulbs at affordable prices? If so, be sure to check out the products available at Bulb Center today!