The ABCDs of LED Tube Lighting: Stay up-to-date on the correct installation of LED lamps and drivers

Published On
Oct 15, 2022

I recently had a two-lamp fluorescent luminaire and ballast go bad in the walk-in closet of our master bedroom suite. The luminaire was an existing fluorescent light with a magnetic core and coil with F40T-12 40W fluorescent lamps and a low power factor ballast.

My first thought was to just replace the lamps, so I made the trip to a big box store to find the proper-sized F40T-12 40W twin-pin (bi-pin) fluorescent lamps. Realizing that this type of fluorescent lamp was no longer sold (these lamps are about as outdated as I am), I looked at my choices.

There were so many lamp types—a normal homeowner would not have a clue about which type and size to buy. How does someone with limited electrical knowledge know what to purchase and whether the lamps would work in their particular luminaire?

I saw a lamp labeled F32T8/SPX/35/IS and found a manufacturer’s description: It was a T-8, instant start (IS), 32W, deluxe specification grade (SPX) lamp with a 3,500K color temperature. Would it work in my old luminaire? I thought it might, but wasn’t sure. There also were T-8, T-10 and T-12 medium bi-pin fluorescent lamps. Then I found the LED fluorescent lamp replacements, with as many different methods of connecting these lamps as there were replacements.

I went from the lamp section to the ballasts, since I decided I would be better off replacing the old magnetic core and coil ballast and using the instructions for the new electronic ballast to find the recommended type of lamp. The new electronic ballasts can be connected to either a 120V or 277V circuit and could be wired into what we called the tombstones (the twin-pin connections in the fluorescent luminaire). These ballasts can be connected to a single lamp, two lamps or up to four lamps using the same ballast.

To be safe, I purchased the entire fluorescent luminaire with LED lamps preinstalled. After installing the new luminaire, I decided to do further research to make sense of all that I had seen! So, here goes.

A Type A LED tube has an integrated driver for use with existing T-8 electronic fluorescent ballasts. Where there is an existing T-8 electronic ballast, remove the old fluorescent lamps and replace them with new T-8 LED Type A lamps. Using an existing electronic fluorescent ballast is not as efficient as using a matched LED system, and the lifespan is affected due to the ballast needing to be replaced before the LED itself. It is also contingent on the Type A LED tubes being compatible with the particular ballast.

Type B LED tubes require the ballasts be removed from the existing luminaire and the power then be wired directly to the sockets. This results in no power loss, since power is not wasted in the ballast, making this system much more efficient than a ballast with Type A tubes.

Having no ballast also reduces future maintenance costs, since the ballast will not have to be replaced. Naturally, the downsides include initial maintenance modifications as the ballasts are removed, as well as potentially having to replace the sockets. Most Type B LED tubes these days can be single- or double-end wired, so if the sockets are in good shape, you can leave the reconnected sockets as-is and just bypass the ballast. Direct power connection to the sockets can be dangerous with connecting sockets to power wires, so strict safety measures are required.

Type C LED tubes use a remote driver rather than an internal one. This remote driver is the difference between Type C LED tubes and the Type A and Type B LED tubes, which have internal drivers. A remote driver can power multiple LED tubes, similar to regular fluorescent lighting; however, Type C LED installations require disconnecting or removing the fluorescent ballast.

Type D LED T-8 lighting (also commonly called Type AB, combo-drive, or dual-mode) is fairly new. Type D LED lamps will operate connected to existing fluorescent ballasts (verify that the existing ballasts are compatible with Type D LED lamps). When the fluorescent ballast finally goes bad, the Type D LED lamps can be directly connected to the line voltage connection of 120V or 277V and could be single-end or dual-end wired based on manufacturers’ recommendations.

Be very careful when working on any ballasted or directly connected luminaire. Disconnecting power to the luminaire is the safest way to work. See 410.130(G) in the 2020 National Electrical Code and 410.71 in the 2023 NEC for the requirements on disconnecting double-ended lamps.

About the Author

Mark C. Ode

Fire/Life Safety, Residential and Code Contributor

Mark C. Ode is a lead engineering associate for Energy & Power Technologies at Underwriters Laboratories Inc. and can be reached at 919.949.2576 and

Stay Informed Join our Newsletter

Having trouble finding time to sit down with the latest issue of
ELECTRICAL CONTRACTOR? Don't worry, we'll come to you.