A19 vs A21 Bulb: What’s The Difference?

Shopping for light bulbs can be overwhelming, especially if you’re unfamiliar with the different terminologies. So, between A19 vs. A21 bulb, what’s the difference? Actually, not much. The difference is mostly in the size. Keep reading to know more about it.

What Do A19 and A21 Mean in Light Bulbs?

A19 is the standard light bulb most U.S. citizens have in their houses, while A21 is the less popular type. However, understanding the meaning of the terms “A19” and “A21” is what matters the most.

Basically, each term consists of two parts, referring to the shape and the size of the specific lamp. Take a look at the following explanation.


Generally, the two most common shapes of light bulbs in the U.S. market have names that start with the letters “A” or “C.”

The letter A stands for “Arbitrary,” which is the classic shape of a light bulb, resembling an upside-down pear. The letter C, on the other hand, is the abbreviation of “Candle.” As you might’ve guessed, it’s the widely known light bulb that looks like a candle flame.


Let’s focus on the series-A bulbs and their different sizes, which brings us to the number following the letter A. Typically, this number refers to the diameter of the bulb’s globe at the widest point, but which measuring unit does it use?

Well, according to U.S. standards, these dimensions are mostly measured in one-eighth of an inch. So, the A19 light bulb has a diameter of 19/8, which equals a bit under 2.4 inches. Similarly, the A21 bulb has a diameter of 21/8, which is around 2.6 inches.

Aside from A19 and A21 bulbs, there are other A-series lamp sizes, including A15 and A25. However, people don’t use them as commonly.

Bulb Base

Mostly, both types of light bulbs come fitted with the same screw base known as “E26.” This is the standard Edison screw bulb base that you easily mount by rotating it into the fixture’s socket.

Since this is the type of socket used in almost all U.S. homes, bulbs with E26 bases usually work with most fixtures.

What Are the Differences between A19 and A21 Bulbs?

Although both types look the same, the most notable difference between A19 and A21 bulbs is the size. Clearly, the A21 bulb is larger than its cousin, not only in diameter but also in length.

While a standard A19 light bulb measures 4.13 inches in height, the A21 bulb is 5 inches long. Usually, a bigger size in light bulbs means higher luminosity. This is why some users might prefer using A21 lamps over their counterparts.

Additionally, the light bulb’s size plays a considerable role in how much heat it gives off. Typically, the bigger the bulb is, the more heat it radiates.

Nonetheless, big bulbs tend to have better heat dissipation. Not only that, but they also have better light distribution than smaller ones.

What Are the Similarities Between A19 and A21 Bulbs?

Talking about the differences between the two types of bulbs obligates us to have a closer look at their similarities.

So, aside from their overall shape and base type, you can expect A19 and A21 bulbs to bear resemblance in omnidirectional illumination. This means they have a 360-degree beam angle as they don’t contain any internal reflectors.

Are A19 and A21 Bulbs Exchangeable?

This question is actually logical. Since both bulbs have the same E26 bases, what prevents them from being exchangeable? Primarily, the answer depends on where you’re planning to use them.

In all cases, you can replace A21 light bulbs with the A19 type. However, when it comes to the other way around, this might not work. That’s because some light fixtures designed for A19 lamps may not be able to accommodate larger bulbs.

Moreover, using an A21 light bulb in fixtures with small lampshades may increase the possibility of fire. Not only because the larger bulb gives off more heat, but also because it’s closer to the lampshade’s fabric.

That’s why it’s quite critical to know exactly what type of light bulb you’re looking for. Plus, being aware of the differences between various bulbs helps a lot.

What To Consider When Choosing Between A19 and A21 Bulbs?

Now that you know the differences between A19 and A21 bulbs, there are a few points to consider when shopping for a light bulb. Aside from the fact of whether they’re interchangeable or not, you should pay attention to a few other factors.

Basically, the size and type of a specific room can highly affect your choice between the two types of bulbs. That’s because, typically, different rooms require different brightness levels.

Kitchens and study rooms, for example, have to be brighter than bedrooms. Therefore, A21 bulbs might be a better option for them. However, bear in mind that with higher lumens, comes higher energy bills. So, if you’re looking to save a few bucks, A19 bulbs may suit you best.

What Are the Varieties of A19 and A21 Light Bulbs?

A19 and A21 bulbs come in three main varieties, which are:

  • Incandescent bulbs
  • Compact Fluorescent Light bulbs (CFL)
  • Light Emitting Diode bulbs (LED)

1. Incandescent Bulbs

The incandescent bulb is the classic type of light bulb containing a metal wire inside called a filament. Although this type is the cheapest of all three, it’s the least energy efficient.

Generally, to produce 1000–1400 lumens, a standard incandescent bulb needs 75 Watts of energy. Additionally, the typical lifespan of any incandescent lamp doesn’t exceed 1,200 hours.

2. Compact Fluorescent Light Bulbs (CFL)

CFL bulbs are slightly more expensive than incandescent bulbs. However, they consume much less energy. Moreover, a CFL light bulb lasts almost 8,000 hours, which is significantly higher than the incandescent type.

3. Light Emitting Diode Bulbs (LED)

When compared to the other two types, LED bulbs are the most energy-efficient and long-lasting. An LED bulb often lasts for a whopping 25,000 hours. That’s probably why it’s the most expensive type of all.