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Understanding Fluorescent Tube Sizes – Which Do You Need?

Understanding Fluorescent Tube Sizes

Fluorescent tube lighting comes in a range of sizes. When you are trying to replace fluorescent lighting, whether, with LEDs or another tube, you will need to understand the difference between tube light sizes.

Determining the tube size of the fluorescent light will help you decide which tube lighting is a suitable replacement. The tube size will also be a clue on the best method for converting fluorescent tubes to LED.

Even if you are not planning on converting fluorescent lights into LED tube lights, knowing about the differences between the sizes is still imperative. Each fluorescent lamp has its own advantages and disadvantages not only because of size but the lumen output (brightness).

Fluorescent Tube Sizes Guide

There are 4 different fluorescent light options; T4, T5, T8, and T12.

The T stands for tubular and the numbers are an index for the diameter (in inches) of the tube. Most tube lighting will have its size mentioned on an end of the tube. So, in most cases, you won’t have to physically measure the tube’s diameter and length.

If the size tag is missing, use the overview below for quick reference.

Tube Light Type Size Index Diameter in Inches Diameter in Millimeters
T4 4/8 0.5 12.7
T5 5/8 0.625 15.8
T8 8/8 1 25.4
T12 12/8 1.5 38.1

Aside from the size, you need to check the lighting fixture requirements for being compatible with the bi-pin base type and the milliamps.

But first, you must know whether you are looking for office lighting with a lot of lumens or something with a softer light as this will make a difference to the option you require.

T4 Fluorescent Lights

T4 Light Tubes for Under Cabinet Lighting

T4 tubes are the smallest of the fluorescent bulb sizes, at only 4 eighths of an inch (0.5 in). Their size is what makes T4 lights popular for under cabinet lighting purposes and accent lighting for displays or a staircase.

There is no industry standard for the length or wattage of T4 tube lights. They can range anywhere from 6 watts to 30 watts, the lower the number the lower the energy consumption, and many lengths.

If you are replacing a T4, you may struggle with finding the same fluorescent light bulbs sizes. Be sure to measure the length of the tube and check the wattage before heading for the shops or placing an online order.

T5 Fluorescent Lighting

T5 Fluorescent Tube Sizes

There is not much difference in size between T5s and T4 lights. This is why the T5 is used in many of the same applications.

On the other hand, T5 tube lights are little powerhouses when comparing T5 vs T8 tube sizes. Compared to a T8, T5 tube can achieve higher luminous flux using less power.

The energy efficiency of the T5 tubes means they also last the longest, around 20,000 hours. However, this is still less than half of the expected lifespan of a T5 LED tube light which lasts an average of 50,000 hours.

If you are using T5 lights for garage lighting or an art display, then make sure that you choose a model with a higher Color Rendering Index, CRi. The CRi of T5 fluorescent bulbs generally range in the lower end of 70 -80 but there are options with more accurate color rendering up to 95. Basically that means the light color can go from daylight white to extra warm white.

Another aspect to remember about T5 fluorescent lighting is the different output possibilities. There are three levels of output available on the market; normal output (NO), high output (HO) and very high output (VHO).

The watts needed for T5 lighting will increase with the type of output. For example, a NO-T5 tube light can range between 14 watts to 35 watts while an HO-T5 fluorescent tube light will usually range between 24 watts and 80 watts.

T8 Fluorescent Lighting

T8 LED Tube Lighting Fixture

The most commonly available is the T8 bulbs. This type of fluorescent tube lighting is the most popular because of its high CRi and many color temperature options.

T8 lights are a good choice for an adjustable lighting system because of their color temperature range from a soft yellow-white to bright daylight. You will also have several options that you can connect to a dimmer.

T8 lights are commonly used in larger spaces as overhead lighting for example in office spaces with troffer lights, garages or classrooms. This is why you will often see long T8 lighting in 4 foot light tubes, 6 feet, and 8 feet lengths.

Compared to T5 lighting, the 8 Foot T8 tube lights are less economical. T8 lighting tends to be more expensive and have a shorter lifespan of around 15,000 hours, but can last up to 50,000 hours if you choose the LED alternatives.

Here’s our top 3 picks for replacement 8 foot T8 light tubes:

JOMITOP 8ft T8 LED Tubes

  • Pack of 4
  • Accessories Available
  • Cool White Color
  • 35+ Reviews

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Read our review
Hyperikon T8/T10/T12 8ft Tubes Lights

  • Pack of 12
  • Excellent Value
  • Bright White Color
  • 50+ Reviews

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Read our review

  • Ultra Bright
  • 70+ Reviews
  • T8/T10/T12 Compatible
  • Business Friendly

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Read our review

If you would like to switch out a T5 light for a T8 light or vice versa then you will need to use a ballast. Finding the correct ballast size may also take some effort as there is no industry standard for them.

T12 Tube

T12 Fluorescent Light Tube Size

T12 lamps are the least popular size. This is because they use older technology that is less energy-efficient compared to the smaller options.

T12 fittings use a magnetic start ballast which is less energy efficient. The smaller and newer models have already been fitted with the more energy-efficient electric ballasts. The ballast is what regulates the current to the fluorescent lamps and provides sufficient voltage to start the lamps

However, there are still many office spaces and homes that use the T12 fluorescent tube lights, especially in older buildings. Another reason why they are still used is the cheaper purchasing price compared to the others, but, they are no longer being made.

Despite being an older model, the T12 fluorescent tube lights still offer a range of color temperatures at different watts. However, their limited lifespan of 15,000 hours still makes T12 fluorescent lights a less attractive option compared to the smaller fluorescent tube lights or LEDs.

Frequently Asked Questions:

Now you know all you need to about fluorescent tubes sizes and their differences. But below we will answer the questions that people ask us the most.

What is the difference between T5 T8 and T12 lights?

In short, the difference between t5, t8, and t12 lights are the sizes and energy efficiency. The smaller t5 and t8 tubes use less energy and have less mercury in them than T12 bulbs.

How do I know which fluorescent light bulb to buy?

When considering the question of how do I know which fluorescent light bulb to buy you need to figure out what you currently have. Once you have removed the bulb most will be marked with the type on the end, if there are no markings then you can measure the tube diameter to determine their type.

What are the different types of fluorescent tubes?

What are the different types of fluorescent tubes? There are 3 types: t12 tubes, t8, and t5 tubes, and the t12 which is the oldest and being phased out and no longer manufactured. The t8 is probably the most used with the t5 being the smallest and most energy-efficient so are often used in large office buildings and warehouses for energy savings.

How long do fluorescent tubes last?

How long do fluorescent tubes last, well that depends a lot on its wattage, design, and application, But, expect between 7,000 and 15,000 hours. But we have seen claims that the T5 can last up to 50.000 hours, but they are the newest on the block.

Think about these differences in tube lighting the next time you need to convert fluorescent lighting to LED. The different sizes are not directly interchangeable so if you want to use another size then you will have to do a bit of handiwork.

Also, don’t forget to compare fluorescent lights with the benefits of LED lighting.

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Odo May 9, 2019 at 10:56 am

Good explanation of the different sizes.

I was just wondering, in your table of sizes, T8 has a Size Index of 1/8. Shouldn’t it be 8/8 to follow the order of the the others?

Patricia Waring November 19, 2019 at 11:55 am

what are the length of sizes 1-8?

David Willis February 28, 2020 at 9:54 am

Hi Patricia,

Sorry I don’t know what you mean, 1-8 what?


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