How to replace old florescent lights with LED

[This is a repost of an entry from 2016, still relevant in 2022.]

I’ve seen interest in how to rewire a fluorescent fixture for LED tubes, so I thought I’d write up some basic info about it.

The first thing to consider is why you want to replace your tubes with LEDs. The two main reasons are energy savings and reliability. If your fluorescents are buzzing, flickering, and don’t come on all the time, it’s a reliability issue. But if you’re just trying to save energy, consider how much you’ll save and whether it’s worthwhile.

A typical 100 watt incandescent bulb burns 100 watts of power (duh) and puts out about 1600 lumens of light (that’s a measure of how bright it is.) A typical single fluorescent tube burns anywhere from 25 to 50 watts and also puts out about 1600 lumens. The LED tubes I linked to use 22 watts and put out 2310 lumens. There is a huge savings going from incandescent to either fluorescent or LED, but LED is only a bit more efficient than fluorescent.

Take out one of your fluorescent tubes and, if you’re lucky, there will be a stamp on one end telling you how many watts and how many lumens. Suppose yours are 40w, subtract the wattage savings (40-22=18 watts) times the number of tubes (6 in my case) 18×6=108 watts. Then multiply by the number of hours per month you have the lights on (let’s say 2 hours/day = 60 hours/month.) 60×108=6580 watt hours. Divide by 1000 to get kilowatt hours (kwh) giving 6.5 kwh/month. You can pull out your electric bill and see how much you would save if you used 6.5 fewer kwh in a month, if your rate is 20 cents/kwh that would be a savings of $1.30/month. You could also go to Home Depot and buy 25W tubes for about $5 each and get some savings. Or use the old office building trick and just remove every other tube from your ceiling. I’ll note that one YouTube video points out the LEDs are brighter, so you might be happy with one LED tube replacing 2 fluorescent tubes: 2310 is brighter than 1600 but not twice as bright.

But if your motivation is to get rid of the buzzing, flickering, and flakiness of fluorescent tubes, the energy savings are just a nice bonus. LEDs are solid, instant on, and last forever. This is why I changed mine.

People ask about daylight vs indoor. That’s called the “color temperature” and you’ll see a number in Kelvin to quote the spec. Personally I don’t care if the light is bright white or blueish, I just want light in my garage. But a woman putting on makeup in the bathroom might have strong feelings about this. Google for “choosing color temperature” if you want to learn about this, and check the specs on what you buy vs what you already have. My LEDs are very bright white, the tubes they replaced were dimmer blue-gray.

Now, about the wiring. Sometimes the tubes just pop in and work, sometimes they require rewiring. I had to learn more than I want to know about this. There are 2 connectors at each end of a tube. A “double ended” fixture has the electric power go in one end (on both connectors or just one), through the tube, and out the other end. A “single ended” fixture has the power go in one connector on one end, then out the other connector on the same end. The other end doesn’t do anything. Fluorescent tubes don’t care which, but fixtures are wired one way or the other. The tubes I used are, according to the manufacturer, double ended, and my single-ended fixture wouldn’t work with them. (I sent them a photo of my fixture opened up, I have no idea how they could tell it was single ended, but they were right.) One of the YouTube videos shows installation of a single ended LED tube.

Now for how to do the rewiring, if you must. First a note about safety. You are working with 110 volts. 110 volts can kill you, or at least buzz your hand. Always unplug the fixture, or shut off the light switch, before working with the wires. (It’s fine to change tubes with the power on as long as there are no bare wires exposed and you don’t touch the connectors.) If it’s unplugged, or the switch is off, you can’t get shocked (unless something is very wrong.)

There are many YouTube videos showing how to do this. I went to YouTube and typed in “how to rewire fluorescent fixture to bypass ballast” and a bunch of them showed up. I recommend them, but remember your fixture and your LED tubes may be different from the one they show.

You’ll need a wire cutter/stripper tool (or a way to cut wire and strip insulation, some people do this with a knife or a long nose pliers) and some wire nuts. Yay – a trip to Home Depot! You also need to be comfortable working with thick electrical wire (if you’ve installed a light switch or outlet, it’s similar) and have a basic understanding of what an electric circuit is. (Take a look at the directions that came with my LED tubes, especially scenarios 2 and 3, and see if they make sense to you.) When you’re bypassing the ballast, basically you want the power to come in on the white wire, into one end of the tube, and out the other end (if it’s double ended) then back to the black wire to go out to the wall. With a dual fixture you want them in parallel (side-by-side): in on the white wire, splice to 2 or 4 wires going to one end of the fixtures, through the two fixtures, back over 2 or 4 wires to another splice with the black wire. Which is black and which is white doesn’t matter, just be consistent. The ballast (big box in the middle) is cut out of the new circuit, the power bypasses it.

Cut the wires as needed, strip of about ½” of insulation from the ends of the wires you’re using, and join them together with a wire nut. (I was too lazy to go to Home Depot for wire nuts so I twisted them into a good mechanical junction with pliers and covered with electrical tape I had.) I can’t overstress the importance of a good mechanical junction – if the wires can come apart your fixture won’t work. Point all the ends the same direction and twist into a good solid spiral with the wire nut or pliers.

When you have all the wiring done and covered with a wire nut or tape, test your fixture before you put the cover (“reflector”) back on. Getting those covers on is a pain and you don’t want to have to take them off again. Put in the tubes, plug it in or turn on the switch, and see if it works. If it doesn’t, either it’s wired wrong or something came loose. Once it’s tested, unplug it, take out the tubes, put the cover back on, put the tubes back in, and test it again. If you’re unlucky and it doesn’t work now, you knocked a wire loose putting the cover back on, so your mechanical junction wasn’t strong enough. This happened to me – what a pain!

Now turn on your lights and enjoy the bright, flicker-free lighting!