Replacing T12 lamps with T8 or T5 lamps. Which one should I use? A user’s guide to upgrading fluorescent tubes.

Beginning in 2013, T12 linear fluorescent lamps were no longer produced by U.S. lighting manufacturers due to Department of Energy regulations. These regulations were meant to encourage T12 users to upgrade to more efficient T8 and T5 lamps and they directly affect many commercial, industrial and retail businesses. Like the dinosaurs, T12 lamps will soon be extinct and their current users will need to decide the best alternatives for their replacement.

What’s the difference between T12, T8 and T5 lamps?

First, let’s decode what the letters and numbers mean. The “T” stands for Tubular, which is the shape of the glass casing for the lights. The associated number represents the diameter of the lamp. This number is the numerator in a fraction where the denominator is 8 and the length is in inches. For example, with a T12, the diameter is 12/8, or twelve eights of an inch. Another way to say this is that the diameter is equal to 1.5 inches. For a T8, the diameter is 8/8, which is equal to 1 inch. For a T5, the diameter is 5/8, which is equal to 0.625 inches. As you can see, the smaller the number associated with the “T”, the smaller the diameter of the tube.

Next, let’s compare the output and performance of each lamp. It’s important to know how quality and quantity of light is measured in order to compare the different lamps.

Quality of light is typically measured as Color Rendering Index (CRI). CRI is a numerical measure of a light source’s ability to reveal the colors of an object in comparison to a natural light source. To put a lamp’s CRI in perspective, the highest possible CRI is 100 (natural light). Here are the average CRIs for each lamp:

• T12 = 62 CRI
• T8 = 85 CRI
• T5 = 85 CRI

Quantity of light is typically measured in Lumens Per Watt (LPW). This is also known as Luminous Efficacy. LPS is the ratio between the total luminous flux emitted by a light source and the total amount of input power (watts, in this case). Here is the average LPW for each lamp:

• T12 = 78 LPW
• T8 = 90 LPW
• T5 = 99 LPW

As you can see, T5s are smaller in diameter and provide a larger quantity of light. They are also 2-3 times more expensive than T8s. The decision to use T5s or T8s will depend on the desired amount of money to spend on them as well as the application that they will be used for.

Application Guidelines for T8 and T5 Lamps

In most cases, the choice between using T5 or T8 lamps depends on the height of the ceiling that their associated fixtures will be hung or mounted from. A good benchmark to use is whether the fixtures are mounted above or below twelve feet. The difference in light output for T8s and T5s is negligible below twelve feet, so it is recommended that a T8 lamp is used due to its lower cost. In the case of fixtures mounted above twelve feet, the T5 lamp is recommended due to better light dispersion.

T12 Replacement Options

Generally, there are two ways to replace existing T12 lighting systems:

• Replace each lighting fixture with a new one containing more energy efficient components such as ballasts and lamps.
• Retrofit each existing fixture with electronic ballast(s) and T5 or T8 lamps. This may also require replacement of lamp holders. There are a wide variety of retrofit kits that can be used to accomplish this task and it is a great money saving alternative to replacing the entire fixture. 

Whatever your needs, it’s time to replace those old T12 lights! See our lamps section to get started.