Closeup on a hand holding an a21 and a19 bulb.

There are several light bulb styles on the market, each denoted by a code. This code ensures that no matter the brand, you will always get the right shape and size of light bulbs. 

A21 and A19 bulbs are some of the most commonly used codes in domestic settings, and if you have ever wondered what the difference between them is, you are not alone.

In this article, we will take a deep dive into A19 and A21 light bulbs. So, keep reading to learn more about how they compare.

What is the Difference Between A19 and A21 Bulb?

A19 and A21 are both type-A light bulbs of different sizes. A19 bulbs are 2.375 inches in diameter and 4.13 inches long. A21 bulbs are slightly larger, with a diameter of 2.625 inches and a length of five inches.

a graphic of an A19 LED light bulb with two arrows pointing to it showing dimensions of 2.4 inches wide and socket base type E26

What are Type-A Light Bulbs?

The type-A light bulb, also known as an A-shape or A-type light bulb, is a common household light bulb with a standard shape and screw base. The shape of the bulb is defined by a set of dimensions and guidelines established by the International Electrotechnical Commission (IEC). 

Generally, type-A bulbs are pear-shaped with spherical end sections narrowing down towards their E26 screw base. The type-A bulb is one of the most widely used bulb shapes and is commonly found in table lamps, floor lamps, and other household light fixtures. 

There are five A type bulbs commonly used in homes, including:

Bulb SizeA15A17A19A21A23
Diameter1.875″2.13″2.375″2.63″2.88″

Type-A bulbs are named for their diameter at their widest point in eighths of an inch. For example, an A19 bulb measures 19/8 inches, or 2.375 inches decimalized. 

A19 Bulbs vs A21 Bulbs

A19 bulbs are sometimes referred to as standard bulbs and are the most common type of light bulbs used in households. They are shaped like a pear and have a diameter of approximately 2.375 inches. A19 bulbs have a medium base (E26) and can be used in various household lighting applications.

a hand in the middle of the picture holding up a lit up LED light bulb with a garden in the background

An A21 bulb is so named because it has a diameter of 21-eighths of an inch or 2.625 inches. The A21 bulb is another common type of pear-shaped light bulb, and like the A19, many domestic light fixtures fit it.

What Types of A21 and A19 Bulbs Are Available?

There are many A19 and A21 light bulbs on the market, including clear, frosted, and coated. They can also be dimmable or non-dimmable, depending on the type of light fixture in which they are to be used.

In addition to these varieties, A21 and A19 bulbs are also available with different types of bulb technology, including incandescent, fluorescent, and LED bulbs.

Incandescent Bulbs

Incandescent bulbs are the traditional light bulb. They use a filament to produce light. The filament is made of a thin wire, usually tungsten, heated to a high temperature by an electric current. 

a closeup of an edison or incandescent light bulb turned on with a black background

When the filament is heated, it produces light. Incandescent bulbs are relatively inexpensive and widely available, but they are not energy-efficient and have a short lifespan compared to other bulbs.

CFL Bulbs

CFL bulbs use a gas-filled tube to produce light. When an electric current passes through the gas, it emits ultraviolet (UV) light, which is then converted into visible light by a fluorescent coating on the inside of the tube. 

Fluorescent bulbs are more energy-efficient than incandescent bulbs and have a longer lifespan. However, they contain small amounts of toxic materials like mercury and take longer to reach full brightness.

LED Bulbs

LED bulbs work by using a semiconductor to produce light. When an electric current is applied, it emits light. The color of the light depends on the specific material used in the semiconductor.

LED bulbs are more energy-efficient and have a longer lifespan than other types of light bulbs because of the way they produce light. They give off very little wasted heat energy like incandescent bulbs, and unlike CFLs, they don’t need any warm-up time and reach maximum brightness instantly.

installing an a19 regular LED light bulb in my desk lamp
While A21 bulbs are a little bigger than A19’s, both should fit in most of the same lamps and light fixtures. This is me replacing my old burned out incandescent A19’s with new energy-saving LED bulbs.

It is also worth noting that LED bulbs are more durable than other types of light bulbs, too. This robustness is because they do not have a filament that can burn out or a gas-filled tube that can break. This quality makes them less prone to premature failure, increasing their expected lifespan.

Are A21 and A19 Bulbs Interchangeable?

Type-A bulbs like the A19 and A21 share the same E26 base type, which means that, mechanically speaking, they are interchangeable. However, due to the difference in their external dimensions, they may not fit into the same lighting fixtures. 

Do A19 and A21 Bulbs Offer the Same Performance?

The lighting performance of A21 and A19 bulbs depends on the specs of the specific light bulbs you are purchasing. However, both types can be bought with the same wattage and lumen ratings, meaning they should provide identical performance, with the only difference being physical size and shape.

However, A21 bulbs, because of their larger size, can dissipate heat more effectively than A19 bulbs and can therefore accommodate higher wattages. This means there are A21 bulbs on the market that exceed the lumen rating of the brightest A19 bulbs. 

Final Thoughts

There are many cases in which A19 and A21 bulbs are compatible and even interchangeable. Before changing an A19 bulb for an A21 or vice versa, be sure that the bulb wattage is suitable for the light fixture, and be sure that the bulb physically fits the enclosure. 

Finally, consider opting for LED bulbs instead of incandescent, halogen, or CFL. Provided that they are compatible with the wattage requirements of your lighting fixtures and have the same E26 base, A19 and A21 LED bulbs are interchangeable with other types of bulbs in those exact sizes.

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