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Light Bulb Shape Guide: Spiral CFLs

Light Bulb Shape Guide: Spiral CFLs

Compact fluorescent lamps, or CFLs, are simply miniature versions of standard full-sized fluorescent lamps. They come in several different shapes and are designed to be a more energy efficient alternative to standard incandescent bulbs. CFLs typically use 50-80 percent less energy and last up to 10 times longer. In this installment of the Light Bulb Shape Guide, we’ll be covering the most popular CFL bulb, the spiral.

Spiral CFL Light Bulb Shapes

Like any other bulb type, spiral CFLs come in a wide variety of sizes. You can find them either bare with the spiral exposed, or covered with a plastic or glass shell designed to look more like conventional A-shaped, globe, or chandelier bulbs. Keep in mind the covered bulbs emit less light than its bare spiral equivalent due to the internal frosting.

Like the other light bulbs in our previous guides, the spiral CFL bulb is identified by a code. Since they are a thin fluorescent tube twisted into a spiral, the code always starts with a “T” for tube and ends with “Spiral.” The number that follows the “T” is based on the diameter of the fluorescent tube, measured in eighths of an inch.

Shape Diameter (inches)
T2 1/4
T3 3/8
T4 1/2
T5 5/8

More importantly, look at the height and width of the spiral. These bulbs can measure anywhere from two inches to fifteen inches, so be sure to measure the space the bulb will be or even the old bulb. Spiral CFLs are a common replacement for incandescent bulbs, so you can also check the Watt Equal spec to help you get a comparable bulb. For example, a 40-42 Watt CFL is a 150W equal, meaning it replaces a 150 Watt incandescent.

CFLs can vary in size, as shown by our helpful, neighborhood LEGO man.

CFLs can vary in size, as shown by our helpful, neighborhood LEGO man.

Spiral CFL Light Bulb Base Types

Spiral CFL bulbs have a large variety of bases. It’s always a good idea to double check what type of base your fixtures use. This chart shows some, but not all, of the base types for spiral CFL bulbs.

Code Type
Candelabra (E12) Screw-in
Medium (E26) Screw-in
Mogul (E39) Screw-in
GU24 Twist-and-lock

Where are Spiral CFL Light Bulbs Used?

Since spiral CFL bulbs come in many different varieties and always have an integrated ballast, they can be used nearly anywhere incandescent bulbs are used. Mini-spirals are able to fit into fixtures usually reserved for smaller bulbs, like table lamps, chandeliers, or wall sconces. Larger spiral CFLs are bright enough to use in recessed lighting for hospitals, retail stores, or schools. They are best used in light fixtures that stay on for longer periods. Constantly turning them on and off, like in bathrooms and closets, can reduce the bulb’s lifespan. Some CFLs are also available for outdoor use, dimmable, shatter resistant, or as 3-way bulbs.

Have you been considering upgrading your home’s lighting with CFLs? Still not sure which bulb you need? Send your questions and concerns to our social media at Facebook, Twitter, Google+, LinkedIn, or Pinterest.

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