A15 vs A21 Bulbs: What is the Differences? - Comparison Guide
A15 vs A21

A15 vs A21 Bulbs: What is the Differences?

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Light bulbs are an essential part of our homes and workplaces, providing us with the necessary lighting to carry out our daily tasks. Among the many types of light bulbs available, the A15 and A21 are two of the most popular bulb types. In this article, we will compare A15 and A21 light bulbs to help you make an informed decision about which one is right for your lighting needs.

Understanding Bulb Size Designations

To comprehend the distinctions between A15 and A19 bulbs, it’s essential to grasp the meaning behind these size designations. The “A” in both cases represents the bulb shape, which typically resembles a pear. The subsequent number denotes the diameter of the bulb in eighths of an inch.

Differences Between A15 and A19 Bulbs

Shape and Size

The most noticeable difference between A15 and A21 bulbs is their size. A15 bulbs are smaller, with a diameter of approximately 1.8 inches and a length of 3.3 inches, while A21 bulbs are larger, with a diameter of approximately 2.6 inches and a length of 5 inches. The difference in size can impact the amount of light produced and the bulb’s compatibility with certain fixtures.

Light Output

Another significant difference between A15 and A21 bulbs is their light output. A21 bulbs have a higher lumen output than A15 bulbs due to their larger size. For example, a 60-watt A15 bulb produces around 540 lumens, while a 60-watt A21 bulb produces around 1000 lumens. If you need brighter lighting, an A21 bulb may be the better choice.

Energy Efficiency

Both A15 and A21 bulbs are available in LED and CFL options, which are more energy-efficient than traditional incandescent bulbs. LED bulbs use less energy than CFL bulbs and have a longer lifespan, making them a more cost-effective option in the long run. When comparing energy efficiency, look for bulbs with the Energy Star label, which indicates that they meet strict efficiency standards.

Dimming Capability

If you want to control the brightness of your light bulbs, you will need to choose bulbs that are compatible with dimmer switches. Not all bulbs are dimmable, so be sure to check the packaging or product description before making a purchase. In general, A21 bulbs are more likely to be dimmable than A15 bulbs, so keep this in mind if you want to use a dimmer switch.

Compatibility with Fixtures

The size and shape of a bulb can affect its compatibility with different fixtures. A21 bulbs are more commonly used in larger fixtures like floor lamps, ceiling fixtures, and pendant lights, while A15 bulbs are more commonly used in smaller fixtures like desk lamps and ceiling fan lights. If you’re not sure which bulb to choose, check the fixture’s packaging or consult with a lighting professional.


A15 and A21 bulbs have their advantages and disadvantages, and the best choice depends on your lighting needs and personal preferences. A21 bulbs produce more light and are more commonly dimmable, while A15 bulbs are smaller and better suited for smaller fixtures. Both bulbs are available in energy-efficient options like LED and CFL, so consider the cost-effectiveness and environmental impact when making your decision. Ultimately, the right bulb for you will depend on your specific lighting needs and the fixtures you plan to use them in.


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