A21 vs A19 LED Light Bulbs
A21 LED light bulbs are the same traditional pear shape but slightly larger than A19 bulbs.
Updated 10/12/23 by 1000Bulbs Staff
Why are Higher Wattage LED Bulbs a Larger Size?
If you've ever searched for a 100-Watt or 125-Watt equal household LED light bulb, you've probably noticed a peculiar phenomenon: the standard A19 shape is often replaced with a slightly larger A21 shape.
This is because light bulb names like A19 and A21 are actually describing their shape through a letter code (A) and the light bulb's diameter in eighths of an inch. A typical A19 is 2.375 inches in diameter (19/8 = 2.375) and 4.13 inches in height, while an A21 is 2.625 inches in diameter (21/8 = 2.625) and about 5 inches in height.
Although the size difference is negligible in most applications, many buyers want to know why higher-wattage household LED light bulbs are made in a larger size.
Man upgrades home light fixtures from incandescent to LED light bulbs.
Where A19 and A21 Light Bulbs are Commonly Used?
The “A” shape was one of the first light bulb designs, and it remains popular in homes to this day. Save for the slightly larger bulb and longer neck, the A21 bulb looks just like an A19 bulb, and it is intended for many of the same fixtures and purposes.
A-shape bulbs usually have a standard medium base that screws into sockets made for all kinds of residential light fixtures, though they are most common in table lamps and ceiling fans. These light fixtures are often paired with 40 to 60 Watt bulbs that produce an average of 450 to 800 Lumens.
However, some homeowners would like these light fixtures to produce brighter light, which traditionally would mean using incandescent bulbs that consume 100 Watts or more. As you can imagine, this is problematic for the energy-efficient minded.
Various sizes of A-shaped LED light bulbs on yellow background.
A Larger Bulb Dissipates Heat
To mitigate this high power consumption, LED manufacturers have been trying to create energy-efficient solutions with 100-Watt equal (and above) A-shaped LED bulbs.
Unfortunately, pesky heat issues can occur when trying to produce so much light with an LED light bulb. Higher-lumen LED bulbs are often made in an A21 shape (and not an A19 shape) because the increased size helps manufacturers avoid overheating issues by providing a larger surface area from which the heat can dissipate more effectively, thus protecting the sensitive internal electronics.
Woman installs A21 LED light bulb in her overhead lighting fixture.
Ensure your A21 Light Bulb Fits Your Application
While making 100-Watt equal LED bulbs in an A19 shape is possible (some manufacturers even go through great pains to make them), 100-Watt equal A21 bulbs are less complicated to produce and are helping speed along the development of higher-lumen, energy-efficient residential bulbs.
As we've said earlier, the size of the A21 bulb will not make a difference most of the time, but it may in some fixtures. Before purchasing an A21 bulb, make sure your light fixture will be able to accommodate the larger measurements!
Row of LED light bulbs illuminate storefront.
Need Help Finding the Right Light Bulb?
For help finding the best LED light bulbs for your fixtures, call 1-800-624-4488 or try our convenient “pop-up chat feature” at the bottom right corner of our 1000bulbs.com web pages.
