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:

  • F17T8/CW/2P: T2 fluoro tubes – 42“ fluorescent tube in a 2-foot length
  • F17T8/CW/4P: T4 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 suggests, mini-tubular are indeed smaller than regular tubes. They are ideal for low-light plant species.

T5 Fluorescent Lighting

Fluorescent lighting is a cheap and efficient alternative to incandescent lights and is great for various uses.

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

T8 Fluorescent Lighting

The T8 fluorescent fixtures are the most common type. Its tube can be between 14 inches and 6 feet long.

T12 Tube

T12 tubes are the most common in the aquarium hobby. These tubes 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.

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:

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 confuse you when searching for the proper lights for your home aquarium.

To cut through the confusion, you can remember that 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: 5/8-inch diameter

T8: 1-inch diameter

T12: 1.5-inches in diameter

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. 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 intensity of the light. The higher the K number, the more intense the light will be.

How long do fluorescent tubes last?

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

In general, an average 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.

Unused fluorescent lights should be taken out of the fixtures. Otherwise, they might 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.

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.


Choosing the right fluorescent tube for your aquarium can be confusing and overwhelming if you're just starting. Our in-depth guide is here to make the process easier and clarify the available options.