Circline Bulb Guide

The Circline fluorescent bulb has been around for decades, but it is still a mystery to many consumers. Not only is the Circline light bulb design less common than more traditional light bulb shapes, but it is also more confusing to replace. There are several different factors to consider when replacing your Circline fluorescent bulbs to ensure that you get the correct light bulbs for your particular fixture.

To help you better understand Circline bulbs, we will take a closer look at what they are and how they work. Additionally, we will address a few common questions related to the fluorescent Circline bulb. For example, how do Circline bulbs work? What are the different sizes available to consumers? How can you measure a Circline bulb on your own? Finally, what do you need to know to properly change a Circline bulb?

In today’s guide, we will answer all of these questions and more, but first, let’s examine how Circline bulbs came about and how they differ from more common bulb designs.

What Is A Circline Bulb?

As you might have guessed from the name, a Circline bulb is a type of fluorescent light bulb that uses one or more tubes to form a circle. Most Circline bulbs have only one tube that forms a perfect circle, with a small base that connects to the socket on a light fixture. It is important to note that, unlike the standard “screw-in” bulb, the Circline bulb uses pins of various layouts to connect to a light source.

Aside from manuals related to sizes and compatibility with different light fixtures, there is very little written about the Circline bulb. Experts believe that it was first introduced sometime in the mid-to-late 1940s. Since then, Circline fluorescent bulbs have been used in homes and businesses all over the world. Despite the fact that Circline fluorescent bulbs are far more energy efficient than incandescent light bulbs, they are not nearly as common because they feature many different pin layouts that make it more difficult to find the right bulb to fit each light fixture.

How Circline Fluorescent Bulbs Work

If you have used fluorescent light bulbs before, you are probably familiar with the long tube design that is commonplace in many offices. These tubes have pins on each end that connect them to the light fixture. While Circline fluorescent bulbs look very different, they work in much the same way.

The sealed glass tube of a fluorescent bulb (regardless of the design) contains a little bit of mercury combined with an inert gas like argon. The inside of the glass is also coated with a phosphor powder. Every fluorescent bulb has some kind of electrode setup that is wired to an electrical circuit.

When a fluorescent bulb is connected to a light fixture with an adequate power source, the electrical current flows through the circuit to the electrodes. The voltage produced by the electrodes causes electrons to migrate through the glass tube. This naturally forces electrons and charged atoms to collide with gaseous mercury atoms, causing the electrons to have higher energy levels. When the electrons return to their normal energy level, they release light photons, which is how fluorescent bulbs produce light.

While this may sound very confusing and complex, it all takes place very quickly. This is why a fluorescent bulb turns on almost instantaneously when you flip the light switch on. As previously mentioned, this process happens in all fluorescent bulbs, including Circline bulbs. With a Circline bulb, the key differentiation is the shape of the glass tube (circular) and the placement of the pins and diodes.

A standard straight-tube bulb has pins on each end to ensure that the electrons flow from one end of the bulb to the other. Since a Circline bulb is circular, it only requires one “base” circuit that interrupts the circle. This is where a Circline bulb can be connected to a light fixture.

Circline Bulb Sizes

There are three standard Circline bulb sizes: T5, T6, and T9. The “T” stands for “Tubular” and the number corresponds to the diameter of the tube in eighths of an inch. Consequently, a T5 bulb has a diameter of 5/8 of an inch (0.625 inches), while a T6 and T9 have diameters of 6/8 of an inch (0.75 inches) and 9/8 of an inch (1.125 inches), respectively.

However, the diameter of the tube is just one part of the equation. If you’re shopping for Circline bulbs, you will likely see a series of letters and numbers in front of the T5, T6, and T9 measurements. These codes indicate the total length of the tube in inches. For example, FC8T9 has an 8-inch tube, FC12T9 has a 12-inch tube, FC16T9 has a 16-inch tube, FC22T5 has a 22-inch tube, and FC40T5 has a 40-inch tube. As you can imagine, a Circline bulb with a longer tube takes up more space.

Additionally, you also have various codes that refer to the size and pin layout of the base. However, it is not as easy to understand these codes based on the letters and numbers alone. For example, one of the most common layouts is the 2GX13 base, which has two pairs of pins facing in opposite directions (4 pins in total). Alternatively, the G10Q base features 4 pins in a square layout, all facing in the same direction.

How To Measure A Circline Bulb

There are two ways to measure a Circline bulb. First, you can measure the diameter of the bulb tube. This will tell you if you have a T5, T6, or T9 bulb. This works using any standard measuring tape or ruler. You simply measure how wide the tubing is at any given point in the circle.

The second way to measure a Circline bulb is by measuring the length of the tube. This will tell you if you have FC8, FC12, FC16, etc. To find out this measurement, place measuring tape along the outside surface of the bulb and measure the entirety of the circle (excluding the non-tube base).

In some cases, you may find that your results come out slightly longer than the standardized sizes. This is due to the fact that you are measuring the bulb from the outside, providing the longest possible measurement. If this happens, you can put your measuring tape along the interior of the bulb as well, record both measurements, add them up, and divide by two. After that, you should be left with a more accurate measurement of your Circline bulb.

How To Change A Circline Light Bulb

Before you do anything, make sure that your light fixture is turned off. Depending on the type of fixture, you may need to remove the covering of the light to access the bulb. Most light fixtures will have moveable parts that hold the bulb in place. Simply remove the bulb from these holders.

Next, you will see that your bulb is still attached to the fixture by a wired socket. You just have to pull this socket out, but make sure to pull it carefully so that you don’t damage the socket chambers. Now, you just have to reverse the process by attaching the socket to the pins on your new Circline bulb, putting the bulb in its place with the holders, and placing the cover back on the light fixture.

We hope you found this guide on Circline bulbs both fun and informative! Are you interested in learning more about Circline bulbs? Are you ready to purchase high-quality light bulbs at affordable prices? If so, be sure to check out the products available at Bulb Center today!