Understanding Fluorescent Tube Sizes – Which Do You Need?

Heather Clouse
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Fluorescent Tube Sizes Guide

Here are the common fluorescent tube sizes with their length, wattage, and lumen output:

  • -F17T8/CW/2P: T8 fluoro tubes – 42 “ fluorescent tube in a 2-foot length
  • -F17T8/CW/4P: T8 fluoro tubes – 42 “ fluorescent tube in a 4-foot length
  • -F17T8/CW/8P: T8 fluoro tubes – 42 “ fluorescent tube in a 8-foot length

T4 Fluorescent Lights

The T4 fluorescent tube is also known as a “mini-tubular.” As the name suggest, mini-tubulars are indeed smaller than regular (34") tubes and are ideal for low-light plant species.

By comparison, the T5 fluorescent tube is usually 2.5 to 3 times larger than a T4 fluorescent tube.

The T5 tube is the recommended tube for aquarium plants. It has a much higher luminescence per watt of power consumption than the T4. More luminescence results in more efficient photosynthesis and better coloration. Larger aquariums tend to need more illumination than smaller aquariums.

T5 are also known as “full-size” or “long-tubed” fluorescent tubes. They are available in lengths of 18, 24, 30, 36, 39, 40, 48, and 55 inches.

If you use a T5 or T8 tube, you will need a fluorescent fixture designed for a 5 or 8 based ballast.

When looking at the shape of the light tube, T5 and T8 have a rounded shape. As a result, you need to select a fluorescent fixture based on the diameter of the lights you will use.

T5 Fluorescent Lighting

Fluorescent lighting is a cheap and efficient alternative to incandescent lights, and are great for a lot of uses.

T5 lighting has become popular in aquarium keeping, and increasingly so over the last few years.

T5 stands for 5/8” tubing diameter, and it’s thelargestoneormosit is still available to aquarium owners. This is often times used to replace the traditional T8/T12 fluorescent lighting fixture.

A lot of people are making the switch from T8 or T12 to T5, and for good reason.

T5 lighting runs cooler and puts out more light than the T8s or T12s did. If your fixture is dimly lit, your yellowing bulbs, or your fixture has a long arc gap, then chances are you can replace it with T5 tubes.

T8 Fluorescent Lighting

The T8 fluorescent fixtures is the most common type. Its tube is 8 inches long and the fixture is called an F8T8.

Light output is 75-82 lumens per watt (LPW) and the life span is about 15,000 hours. Don’t worry too much about the lamp’s life span, because it’s very unlikely that you will actually use it for that long.

Unused fluorescent lights should be taken out of the fixtures because they start to lose brightness even when they are turned off. Without use, the lamp life is about a year. Just keep them away from direct heat and you should be fine.

Tubes are manufactured with different colors, so choose the right color for the particular area of your aquarium you want to illuminate. Since different colors will emit different wave lengths and intensity, choose the one that best suits your fish.

T12 Tube

T12 tubes are the most common in the aquarium hobby. These tubes are produced by three major manufacturers in the U.S. These manufacturers produce similar quality tubes but in slightly different thicknesses. Thus, they range in wattage from 13W to 20W. The T12 tube’s slim size creates an attractive style but you must use care in how you use them in your aquarium.

Each manufacturer makes tubes that are specifically suited for aquarium use. They all tout their more natural colors but each one has their own “special” formula. Many companies also manufacture filters, heaters and other such products that can utilize T12’s directly.

The most popular are the 13 and 15W tubes made by Coralife, but the 18W made by Oceanic and the 20W made by Marineland are also good alternatives.

Whichever tubes you choose, you can use any of them in a 24” x 12 ” standard fish tank. If you are planning a larger tank where you would like to use two or more tubes, make sure that you use a tube wattage that is below the maximum recommended wattage for fish life.

Using more powerful tubes will work, but you will be more likely to encounter additional problems.

Frequently Asked Questions:

Can you put the same size tubes inside each other for a smaller size, e.g., a T8 inside a T12?

No, not a good idea as the inner tube will have to fight against its own outer diameter. * Can you put a double wall fitting with one single or double tube inside another tube/fitting of a different size, e.g., a T8 inside a T12 tube?

No, the fitting will try to make the outer tube smaller so… no go. Get the correct size as this is how it should be. * What are the tube types and sizes used for different applications?

  • Tubes used for general lighting are called tubular fluorescent lamps and come in four sizes: 2‘, 4‘, 8‘, and 12‘.
  • Smaller wattage tubes are often called mini-tubes, mini-strips, or compact fluorescents (CFLs).
  • Larger wattage tubes are called high output (HO) fluorescents. Some people refer to them as ‘triphosphor’ bulbs.
  • There are other sizes of fluorescent tubes as well, but these are the most common.

What is the difference between T5 T8 and T12 lights?

Fluorescent lights are commonly used as compact fluorescent lights (CFLs). But you may also hear them referred to as T5, T8 and T12 lights, or T-bulbs. This can cause confusion when searching for the proper lights for your home aquarium.

To cut through the confusion, you can remember that T8 and T12 light bulbs are the same as T5 light bulbs. Manufacturers started to identify the bulbs by the tube diameter to distinguish the different lengths of the T5 tube. Each one of these bulbs is also referred to as a form, so the shortened technical name of the bulb is T5 T8 T12 form.

These three terms refer to the bulb length, so the light tube lengths are:

T5: 1-inch diameter, medium length

T8: 2-inch diameter, extra-long length

T12: Right between the two, 1.5-inches in diameter, extra-long length

T5 and T8 are the most commonly used tubes in today’s aquarium market. Both tubes are very similar in length and performance. They do differ, however, in the light spectrum that they produce.

How do I know which fluorescent light bulb to buy?

You have a few different dimensions to consider when buying a fluorescent light bulb.

The T8 is the most common size used. But there are also others out there to choose from, including T5 (longer tube) and Rapid Start (shorter tube). Talk to your local home improvement store and your local electrician expert about which is best for your needs.

The most important thing you need to know when buying a fluorescent light is the “K” rating … or the intensity of the light. The higher the K number the more intense the light will be.

What are the different types of fluorescent tubes?

These are used to light a broad, even area. They are a good all-purpose light that is easy to install and very inexpensive.

They are available in a huge range of wattages, so you should be able to find one that suits your needs.

Fluorescent Tubes

They are available in three main types: compact fluorescent bulbs, linear fluorescent bulbs and fluorescent tubes. They are all thinner than normal bulbs and take up less space.

They’re better for illuminating large, dark areas.

Fluorescent tubes (also known as T5 bulbs) are a very flexible type of fluorescent and are ideal in commercial settings (in high-ceilinged buildings, long corridors, etc.) They are more expensive than the other types of tubes, but they are very efficient.

They’re available in a huge range of lengths and wattages. They’re known as “tube lights,” and that’s what they look like. You can see them above in the picture.


These are more expensive than normal bulbs (but less expensive than tubes) and are also curved. However, you can’t actually tell that they’re curved unless you look closely.

How long do fluorescent tubes last?

The lifetime of a fluorescent tube depends on several factors including the type and brand of fluorescent tube you have as well as the environment and how well you look after it.

In general, an average 18-inch fluorescent tube has a lifespan of about six to eight months. However, this is just an average and most tubes will last longer than that.

The main thing is to not let them operate beyond the rated lifetime because this will lead to a drop in efficiency and light output.

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