Understanding Circular Fluorescent Bulbs

This post has been updated from its original 2013 version.

These round bulbs pack a few more features than their fun design suggests, and if you are not savvy to the ways of circline lamps you may have a hard time incorporating them into your home’s lighting. To fully understand and get the best out of circular fluorescent bulbs, keep the following four facts in mind.

Pay Attention to Wattage

Just as with (the soon to be gone) standard incandescent light bulbs, circline lamps use wattages to measure how much power is used to light a bulb. By comparison, the circular fluorescent lights emit the same amount of light (lumens) while using less power than incandescents. A circline light bulb of only 13 watts can replace a 60 watt incandescent bulb and has an output of 650-900 lumens. The wattage of the bulb also determines the diameter of the bulb which in turn determines if it will fit the fixture. So unlike standard spiral CFLs you may not be able to go up or down in wattage range because it will affect the size of the bulb possibly rendering it unusable with your fixture.

Color Temperatures Are the Same as Standard CFLs

Color temperatures represent how bright a bulb is. Circular fluorescent bulbs can range in color from warm white to the brightest daylight just like standard compact fluorescent lights. Color specifics are all varying shades of white:

  • 2700K: Warm, equivalent to what is typical in a bedroom or living room
  • 3000-3500K: Soft, suitable for bathrooms
  • 4100K: Cool, florescent-like in color
  • 5000K: Daylight, the brightest color, like sunlight at noon

Circular Bulbs Cannot be Used in Just Any Fixture

This is where using a circular fluorescent can get tricky. Depending on the manufacturer, some light fixtures only use bulbs from their own line. Yeah, I know it can be tempting sometimes to go with an off/generic brand, but in this case your generic circline lamp may not work in the fixture. When replacing a Circular Lamp, first make sure that there are no manufacturer specifics determining what bulb can be used. Next, determine what the lamp type (e.g. T6 , T9) and pin type is (e.g. 2 pin, 4 pin). When finding the right lamp for your fixture, you have to choose the same lamp type and pin types as these are not interchangeable.

Diameter Matters

For light fixtures that use circular bulbs that are too big or too small will not work, even if it is from the right manufacturer. Make sure to replace these bulbs by measuring the diameter of an existing bulb then purchase the right size. If you would rather leave measuring alone, you can also use the manufacturer model number to find a replacement bulb.

While there is more to be taught and learned about circular fluorescent bulbs, these four facts alone will allow you to make informed purchases and hassle-free replacements. See, it doesn’t take much to become savvy to the ways of circline lamps.

Shop for Circular Bulbs>>>

TCP 32020 20W T9 4-Pin Circular Lamp 27K
TCP 32020 20W T9 4-Pin Circular Lamp 27K
TCP 58W T-6 4 Pin Circular Lamp CFL Bulb 3205841K
TCP 58W T-6 4 Pin Circular Lamp CFL Bulb 3205841K
Philips 22w T5 4 Pin Circular CFL Bulb TL5C-22W830-1CT/1
Philips 22w T5 4 Pin Circular CFL Bulb TL5C-22W830-1CT/1



6 thoughts on “Understanding Circular Fluorescent Bulbs

  1. Jeff Deutsch says:

    Circline bulbs are not CFL’s. CFL bulbs contain their own ballast. That is why they can directly replace an incandescent bulb. Circline bulbs use an external ballast like a straight tube fluorescent. Generally, any fluorescent is about 5 times more efficient than an incandescent.

  2. Donna says:

    My circular tube light when turned on at switch stays on a bit, 5minutes or so, then goes off a bit, then comes on a bit, then goes off. Is this normal. What to do?

  3. David says:

    I bought an 8″ Circline Bulb (22W) to replace dead bulb in bathroom ceiling fixture without taking the old one in (couldn’t remove locking clip in the dark). Turns out the old one is a 9″ 30W Circline Bulb. I installed the 8″ anyway and have it mounted to one clip and the connector (which has an anchor) My question is…. is there any risk in have the slightly smaller bulb up there? It lights right up. Am I ok? Thanks in advance

  4. Rhonda says:

    I bought a 9″ circular bulb (30W) to replace a burnt out one. The new bulb match identifiers codes match the burnt one. I replaced the bulb. the new bulb does not light up around the entire structure. It only lights up about 2 inches from the insertion source. Why? What is happening?

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