How to measure fluorescent and LED light flicker

Friday, February 26, 2016

How to measure fluorescent and LED light flicker


Fluorescent tubes flicker because of their inherent design. LED lights may or may not flicker depending on how well their power supply is designed. How do you measure the amount of flicker? In this episode, we quantify the flicker in the fluorescent tubes and after an LED light conversion.

How to easily convert fluorescent tubes to LEDs:
Electronupdate video: Measuring Light Bulb Flicker with Nothing More Than a Cell Phone:

For a written transcript, go to How to measure fluorescent and LED light flicker

Music under Creative Commons License By Attribution 3.0.
Intro/Exit: "Hot Swing" by Kevin MacLeod at


After seeing last week's episode about converting fluorescent lights to LEDs, David Terry asked "do they flicker the same way fluorescent tubes do?” I wasn’t sure, so let's measure and find out, today at the House of Hacks.


Hi Makers, Builders and Do-it-yourselfers. Harley here.

Fluorescent tubes are powered by AC current and flicker based on the speed of the power cycles. Here in the United States, our power cycles at 60 hertz. This means the hot lead varies between positive voltage and negative voltage 60 times a second. The tubes don’t really care about positive or negative values, just the absolute value and so will flicker at twice that rate, or 120 times a second.

This is too fast to bother most people, but a non-trivial segment of the population are affected by this and have problems working under fluorescent lights. The flicker can also cause artifacts when shooting video at certain frame rates. And, as the bulbs age, they may not go on and off at every cycle, causing the flicker to slow down and become more noticeable.

To measure the flicker, I've got this simple setup. I have just a solar cell and the oscilloscope. The flicker in the lights will cause the output of the solar cell to oscillate in sync and the scope allows us to see that variation. At 120 times a second, we expect to see each cycle to be around 8 milliseconds so I have the scope set to 10 ms per division.

Now I'm going to connect the scope to the scope to the solar panel. And we’ll see what we have here… and that's exactly what we expect to see; each cycle is about 8 milliseconds.

So now I'll go over into the room other room and check it out with the LEDs.

I still have exactly the same setup as I had before. Let’s connect the scope to the solar panel and see what we get.

Ah, a straight line. So, to answer David’s question: no, there is no flicker with these LEDs. Thanks David for asking the question.

And coincidentally, a couple days ago an electronics channel I subscribe to, electronupdate, uploaded a video showing how you can use a cell phone to detect this flicker. I thought you might find that interesting.

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