I noticed that my eyes feel tired with certain fluorescent lights in my office. I read that low frequency fluorescent lights can make eyes tired. Is there a tool I can purchase to measure the frequency of a fluorescent light source?

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    Lobby your employer to switch over to led tubes. If they say no and if your office is not to big you could replace them your self. Get the the kind that plug and play, meaning no need to bypass the ballast. You can choose the brightness ( lumen's ) and the color temp ( kelvin ). i prefer natural daylight temp of 5500k but 4000 to 5000 will be nice.
    – Alaska Man
    Nov 3, 2018 at 21:16
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    Can you hear the ballast audibly humming at the usual 60Hz frequency the way transformers do? Nov 3, 2018 at 22:38
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    get a desk lamp with an incandescent lamp to illuminate your work area .... it may help
    – jsotola
    Nov 3, 2018 at 23:05
  • Us humans do not do well living under artificial lighting that doesn't have a balanced spectrum of red versus blue. Fluorescent light fixtures aren't as bad as LED. jsotola is right. Get incandescent to illuminate you in your work area!
    – stormy
    Nov 11, 2018 at 23:32

5 Answers 5


I personally have done this with a Greenlee clamp meter, a volt-meter with a Hz setting. I connected the meter to the terminals at the non-shunted end. Only do this with a Cat II or higher rated meter and only after the light has lit. Otherwise the meter will be subjected to the ignition voltage of near 1kV.

I rather liked the high-frequency ballasts that I installed. Went from 60Hz to 48kHz. These were Philips high frequency electronic ballasts.

I got T12 because I didn't want to replace the bulbs. I really should have at the time got T8 ballasts and replaced the bulbs.

I would not have traded for LED tubes. Most the the LED tubes are poor replacements they tend to be far too blue and also lack diffusers so you end up with point light sources brighter than the sun. Which exceeds the recommended the luminous contrast ratio between light and dark areas in a office work space. The point light sources are so bright that they make the area effectively darker.


2 possible answers here. What you need is an oscilloscope to measure the output frequency of the ballast. Yes 50 or 60Hz goes into the ballast but the output of electronic ballast do have a different frequency. I would just open the the fixture and get the ballast model number and look it up on line or call the mfg. Much cheaper than getting a scope, even a home built with a micro controller cost 30$. 2nd It can be the wavelength also. If you notice headaches with Flouresents that are slightly yellow in color these can have a color frequency of 2500K with the number increasing to 6500K for a very bright outside like color with values in between this wavelength or color is Independant of the ballast frequency and usually stamped on the tube.


The flicker rate of fluorescent tubes has been a subject of considerable comment and discussion for as long as I can remember. I had a friend who designed the lighting in a new office building he was fitting out for relocating his own financial firm. This was San Francisco Bay area in the 1980s or 90s. In a large open area with cubicles he had the 48" tubes side by side on different legs of the electrical system. He told me that this would reduce the flicker effect. He had some valued employees in the old location who complained that the fluorescent light flicker in the old place was irritating and fatiguing.

I think it was overwork that was fatiguing the employees; this guy had many virtues but he was a workaholic employee-driver. He said he got no more complaints from his employees, even though productivity and work hours increased at the new location. I told him that I thought this might have been the power of suggestion because I thought that this could not have improved the received flicker since it would have been 2-times the 60 Hz and the two legs would flicker in phase not out of phase. But @Harper comments below that with 3-phase power putting the lights on different legs would reduce flicker.


Fluorescent lamps using conventional magnetic ballasts flicker at twice the supply frequency. Electronic ballasts do not produce light flicker since the phosphor persistence is longer than a half cycle of the higher operation frequency of 20 kHz. The 100–120 Hz flicker produced by magnetic ballasts is associated with headaches and eyestrain.[12] Individuals with high critical flicker fusion threshold are particularly affected by light from fluorescent fixtures that have magnetic ballasts: their EEG alpha waves are markedly attenuated and they perform office tasks with greater speed and decreased accuracy. The problems are not observed with electronic ballasts.[13] Ordinary people have better reading performance using high-frequency (20–60 kHz) electronic ballasts than magnetic ballasts,[14] although the effect was small except at high contrast ratio.

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    I also know some folks are affected by low color frequency color lights. When I worked for a major manufacturing company we relamped entire buildings with 6000k and some of the problems associated from Flouresents disappeared (these already had electronic ballast) also these lamps improved productivity and reduced SAD issues that plague Oregon.
    – Ed Beal
    Nov 3, 2018 at 20:46
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    It worked because he had 3-phase power and the poles are 120 degres out of phase, not 180. Powering the twin lamps with any 2 phases would have pulled the flickering off-beat from each other. Powering 3 lamps with all 3 phases would all but eliminate it. Alternately he could have used electronic ballasts and eliminated the problem entirely. Nov 3, 2018 at 22:41
  • @Harper, OK so my friend may have been right about his intervention reducing the flicker. Was this a common technique for reducing flicker? (I talk about him in the past tense because he moved away and we have not maintained contact.) Would the standard 1990s office building have been supplied with 3-phase? What about now? Nov 3, 2018 at 23:21
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    Yes and yes. All the power in commercial districts is 3-phase. Residential style split-phase is hard to acquire, easier to get 208Y for 120V circuits. As a guy who wires a lot of lights, I would consider it an "eccentric" way of solving the problem, because it's a lot of extra wiring. If it were me I would have specced the early electronic ballasts and called it done. Nov 3, 2018 at 23:29

Yes. A vintage turntable.

Many record turntables had markings along their edge. Those were designed so under lighting that shimmered at 60Hz or 50Hz (like all lighting in the 80s, somewhat), the markings would "stand still" when the turntable was going the correct speed.

Your fluorescent lights should:

  • Not flicker at 50Hz, 60Hz or any other frequency anywhere near those. Even a hummingbird should perceive them as solid light.
  • Not strobe on or off or be annoying with lack of brightness.
  • Not be green or gross: be the color temperature you want.
  • Make everything they are lighting look beautiful and realistic.

If it is failing on the first two, change the ballast to an electronic ballast. If it's an outdoor application where you'll be in the frigid cold, use a programmed-start ballast which knows how to preheat the tubes to the right temperature before it starts them. Also use programmed start for its soft start, if it's frequently turned on or off, or in a hard-to-service location. Change the ballast to T8 and get T8 tubes.

If it's failing on the second two (and you've already got modern electronic ballasts), go buy new tubes. The newest tubes are any color temperature you want, and 90 CRI or better. I get Sylvania 4100K 90CRI tubes for about $20 for 12 tubes.

They also make old style T12 tubes with CRI as high as 98 (100 is perfect), but only do that if you have a modern electronic T12 ballast. I fit T12 electronic ballasts in my paint room a few years ago, some 98 CRI tubes will be a perfect complement.

At that point, you will forget you have fluorescent tubes.

You can get most of this win by going with LED "tubes", (you want direct-wire, opposite-end power), but if light quality is your top priority, real fluorescent has a slight advantage.


That's easy: it's the same frequency as your electric supply (50Hz or 60Hz), an easy test you can do is using skype webcam setup: try setting the flicker reduction to 50 Hz, if flicker on the screen disappear so you have 50Hz flickering, if flickering doesn't go away, try with 60 Hz, I'm almost sure that you'll find the frequency this way.

  • Unfortunately this is not true with modern electronic ballasts, it would be true with magnetic ballast but at least in the U.S. they have not been available since around 2002 and electronic ballasts have been available since the 90's maybe longer.
    – Ed Beal
    Nov 3, 2018 at 20:31
  • If it was an electronic ballast, he wouldn't be complaining! Nov 3, 2018 at 22:39
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    And if it's magnetic ballast it'll be twice the line frequency, ie 100 Hz or 120 Hz. The lamp does an on-off cycle for each half-cycle of the incoming AC. A photocell and a scope will tell you this. Nov 4, 2018 at 3:14

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