5 Different Fluorescent Tube Sizes and How to Choose One

In This Article

What Is a Fluorescent Light?
Fluorescent vs. LED Bulbs
Types
Fluorescent Tubes vs. Bulbs
How to Choose
FAQ

For now, long-lasting fluorescent light fixtures are commonly found in the home in garages, workshops, and basements to provide light for workbenches, hobby areas, and to grow plants. Fluorescent light tubes are glass lamps that use fluorescence to produce light. (Fluorescence is the result of certain chemicals giving off a visible light).

Although LED (light-emitting diode) light bulbs are increasingly popular and have largely replaced standard incandescent light bulbs, traditional fluorescent lights (lamps) still have their place in the home. In addition to long horizontal fluorescent light tubes, there are also screw-in fluorescent lamps called CFL (compact fluorescent lamp/light) bulbs. CFLs were once regarded as an excellent energy-saving alternative to incandescent bulbs until the advent of LED technology, which has led to a movement towards phasing out the technology.

The 9 Best Light Bulbs of 2024

What Is a Fluorescent Light Tube?

All fluorescent tubes (lamps) consist of a sealed glass vessel that contains a small amount of mercury and an inert gas, usually argon, at a very low pressure. The inside of the tube or bulb is coated with phosphor powder. When the light fixture is turned on, electrodes inside the tube or bulb ionize the mercury vapor, causing light to be emitted when the ionized atoms strike the phosphor coating lining the glass.

On the other hand, incandescent bulbs produce light when an inner metal filament gets hot enough to glow from the electricity passing through it. LED bulbs produce light from electrical current passing through microchips.

Fluorescent Tubes vs. Fluorescent Bulbs

One legitimate reason why the use of fluorescent bulbs is not as common as the use of LED bulbs is that fluorescent bulbs contain a small amount of hazardous mercury. This makes it difficult to dispose of fluorescent light bulbs safely. Always consult your local waste management agency for advice on what to do with burned-out fluorescent bulbs. Another reason to avoid fluorescent lighting is that LEDs are more cost-effective over the long run. Though more expensive initially, a good-quality LED bulb can last three to five times longer than a CFL bulb.

Types of Fluorescent Lamps

Fluorescent tubes come in five basic types, identified as T2, T5, T5HO, T8, and T12. The "T" designation stands for "tubular," and the following number refers to its diameter in 1/8-inch diameter increments. A T12 bulb, for example, is 12/8 inch in diameter, or 1 1/2 inches. A T2 bulb, on the other hand, is 2/8, or 1/4 inch, in diameter.

Here's what you should know about each basic fluorescent tube size and bulb shape if you plan to replace a flickering bulb in your home.

01 of 05
T2 Bulbs

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- Best for: Replacing incandescent bulbs in light fixtures and lamps.
T2 fluorescent bulbs have tubes that are 2/8, or 1/4 inch, in diameter. This is the size that is often used for CFL (compact fluorescent light) bulbs that are configured to screw into standard 120-volt light fixtures and lamps. There are also straight T2 tubes that are often used for the table lamps that provide task lighting used for crafting and sewing.

In CFL bulbs that screw into standard light fixture sockets, the ballast that steps up current is integrated into the screw-in base rather than placed in the light fixture itself. This allows the CFL bulb to be used in standard light fixtures that can also accept incandescent or LED bulbs.
02 of 05
T5 Bulbs

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- Best for: Task lighting in kitchens, low ceiling fixtures.
T5 tubes are 5/8 inch in diameter—larger than the tiny T2s, but smaller than the larger tubes normally used in shop lights. These bulbs are space savers but still put out the same amount of light as the larger bulbs. These bulbs are good for fixtures mounted on lower ceilings and on the underside of cabinets above countertops. Add these to your kitchen to give you a balanced lighting scheme of soft light that is sure to please. Being small, the space required to accomplish this lighting task is minimal, and the result is great. People use these above and below cabinets to add a unique look to their kitchen, but kitchens are not their only use. Be creative in using these space-saving light bulbs.
03 of 05
T5H0 Bulbs

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- Best for: Exceptionally bright illumination; large, tall rooms.
T5H0 bulbs are identical to the T5 bulbs with one exception—they are much brighter (HO stands for "high output). These bulbs are said to be twice as bright as T5 bulbs. They are a great addition to rooms with taller ceilings. These bulbs used in fixtures can be great accent lighting in rooms with wall-mounted pictures, and areas that require more light, such as rooms with tall ceilings. These bulbs are so powerful that they are often used in the up-high fixtures used in warehouses and warehouse stores.
04 of 05
T8 Bulbs

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- Best for: Outdoor light fixtures.
T8 bulbs are 1 inch (8/8) in diameter. They are more expensive than T12 bulbs but will start much faster. They are excellent at starting at all temperatures, including temperatures below freezing. The starting temperature is set by the type of fluorescent fixture ballast you have installed in the fixture that you buy. The ballast is responsible for starting the light fixture and determines the type of bulb required in each fixture.

Be sure to do your due diligence before making a selection of light fixtures, especially if you need a cold weather-start light fixture. A rapid-start, instant-start, or electronic-type ballast may be the right choice for you. Your local dealer can help you choose the right fixture if you give him or her the parameters of your needs for your installation.
Continue to 5 of 5 below
05 of 05
T12 Bulbs

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- Best for: Industrial uses, warehouses.
T12 tubes are 1 1/2 inch (12/8) in diameter. They are bigger, bulkier, and the least expensive to buy, although, they are not the most efficient tubes. The biggest drawback of these tubes is that they are warm-weather bulbs. They need temperatures to be 60 degrees Fahrenheit or higher to start and operate properly. Below that temperature, the light may appear to flutter and is much dimmer during start-up. The color of T12 bulbs tends to be somewhat greenish, so they are not commonly used in residential applications.

These are now less popular as users have migrated to smaller and more efficient T5 and T8 tubes. Older factories are seeing the benefits of moving away from these older-style tubes, and with the new age of LED lighting, it looks as though the days of these old-style fluorescent tubes are numbered.

Fluorescent Tubes vs. Fluorescent Bulbs

In a fluorescent tube, there is an electrode at either end of the tube. A device known as a ballast steps up the 120-volt line current in the circuit to a level sufficient to energize the mercury vapor within the tube. The electron flow moves from the electrode at one end of the tube to the electrode at the other tube, and light is produced as ionized mercury atoms strike the powdered phosphor that lines the inside of the tube.

A screw-in fluorescent light bulb is essentially a miniaturized version of the long bulbs used in shop lights and similar fixtures. In the bulb version, a miniaturized ballast is integrated into the base of the screw-in portion of the bulb. Most screw-in fluorescent bulbs consist of small T2 tubes tightly coiled together so that the bulb remains roughly the size of a standard incandescent light bulb.

How to Choose a Fluorescent Light Tube

The tube must match the specifications of the light fixture—A T5 tube will not fit in a fixture designed for T8 fluorescent lamps. The exception is CFL T2-size bulbs, which will fit in any standard screw-in light socket.

There are several other considerations when it comes to matching a fluorescent tube to a specific fixture:

Bulb wattage: Light fixtures will be rated for the wattage of fluorescent tubes they accept. This will vary according to the diameter and length of the tube. For example, T12 bulbs are typically 48 inches long and use 40 watts to provide 2500 lumens of light output. T5 bulbs, on the other hand, are typically about 45 inches long and use only 28 watts to produce the same 2500 lumens of light output.
Light output (Lumens): This is a measure of the amount of illumination provided by the fixture. The higher the number, the brighter the light.
Color rendering index (CRI): This refers to the color of the light produced, on a 100-point scale, where 100 is the relatively warm light produced by standard incandescent light bulbs. CRI ratings under 70 tend to produce a greenish color that's not all that pleasing. For most residential use, ratings of 80 to 89 are considered best. T12 tubes generally have a CRI of about 62, while T5 and T8 tubes have a more realistic CRI of 85.
Correlated color temperature ( CCT): is a measurement of the color appearance measured in degrees Kelvin within a range of 2700K to 6500K. 2700K is the warmest (closest to yellow) and 6500 is the coolest (closest to sunlight). Most light fixtures will allow you to choose tubes with different CCT ratings. If you are using the fixture as a grow light for plants, for example, you'll want to choose one with a color temperature close to natural sunlight.
Shape: Your light fixture may accept traditional straight tubes, or it may be designed for curved or round tubes. CFL (compact fluorescents) have narrow tubes that are coiled to create a shape roughly the size and shape of traditional incandescent light bulbs so that they can be used in standard light fixtures.
Base type: Most common fluorescent light fixtures use bases with two pins that fit into slits in the light fixture. But CFL bulbs have screw-in bases that fit standard light fixtures. There are also single-pin tubes designed for fixtures with that socket design.

FAQ

Can you replace a fluorescent light with an LED?

You can replace many outdated fluorescent lights with LED bulbs. However, some of the tubes and bulbs can be directly replaced while others are not always easy or direct replacements because of the ballasts. For example, you may need to look for LED tubes specifically designed to retrofit linear fluorescent lamps.
Are fluorescent bulbs being discontinued?

The short answer is yes. States are beginning one by one to ban or restrict the manufacturing and sales of CFLs and LFLs (tube-style linear fluorescent lamps) in favor of LED bulbs. The federal government is looking to phase out all fluorescent bulbs by 2025 though states are not waiting that long to take action.
Which is brighter, LED or fluorescent?

Overall, LED and fluorescent lights produce nearly the same amount of bright light. LEDs may be slightly brighter but they are much more cost-efficient.

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