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I had a brief exchange with Dr. Jack Kruse on Twitter the other day. He made the claim that using incandescent lamps with dimmers is bad for your health. Well that certainly got my attention as I am a huge proponent of using dimmers. There are dimmers on most fixtures in my home and I recommend others do the same. Check out the conversation:

His concern is that flickering, just outside of conscious perception, will wreck havoc on your health. Now I’m no neurosurgeon (and I’ve no clue what “aQA 4 gate” is), but I do know a thing or two about lighting and electricity.

How modern dimmers work

Incandescent lamps work by running an electrical current through a tungsten filament. The filament gets super hot and radiates light. For lower light output you need the filament to be cooler. That’s what a dimmer does. It lets you adjust the heat (power) output of the lamp.

So how does a dimmer lower the power output of the filament? In AC voltage systems, voltage cycles from 0V to a positive peak then down to a negative peak and back to zero. For a United States standard 120V system, the cycle has a peak of 170 volts with the voltage going to zero twice in the cycle. There are 60 cycles a second in the US. So that’s 120 times a second that the voltage supply to a lamp hits zero!

A dimmer elongates the time that the sine wave is at zero volts. Jack is correct in that the AC sine wave is “chopped up”. There is an electronic gate with an adjustable time delay that closes when the voltage hits zero. When the dimmer is turned all the way down, the delay is longer and when its at full brightness there is no delay. The longer the period of zero voltage, the cooler the filament will be.

The chart below shows four cycles of an AC voltage sine wave. Regular line voltage is shown in blue and the dimmed voltage in red.

Dimmer Sine Wave

You see that the voltage on the red wave stays at zero for a longer period of time before jumping up to 170V then back down to zero. Notice that there is no ramping up. The voltage jumps from 0 to 170V before tapering down.

Where I was wrong

When a lamp is not dimmed the light cycles at 120 Hz. The light pulsates very slightly as the filament cools and reheats 120 times a second. A full power incandescent lamp has very little flicker. As you begin to lower the light level you are reducing the frequency from 120 Hz down to 30 Hz or even less depending on the dimmer. I thought that a filament would not cool and heat at a magnitude necessary to produce any meaningful flicker but I was wrong. At Jack’s prompting, I have found that flicker in lighting, even my precious incandescents, can indeed be a problem! I was also shocked to learn that some people are sensitive to light flicker at well over 120 Hz.

Health concerns

So far I haven’t found much besides the usual: eye-strain, headache, and of triggering epileptic seizures. Of course that’s very bad for epileptics, but what about the rest of us? Unfortunately, there doesn’t seems to be a whole lot of research beyond that. I did look into Alexander Wunsch who Dr. Kruse referenced in his tweet. There is a lot of great information on artificial light, unfortunately a large portion is in German. I haven’t yet found anything directly addressing the problem of light flicker.

What now?

I have a lot of research to do! Flicker is something that is not regulated at all and has no set industry standards. Incandescent lamps are at least fairly consistent with regards to flicker. LED flicker can be very problematic because it can vary from 100% to 0% and it is vary hard to test what you’ve got without expensive equipment. There are no labeling or reporting requirements from manufactures. My recommendation is to use brand-name incandescent lamps and brand-name (i.e. expensive) dimmers, and not to dim more that 50%. I still use a amber LED light as a bedside light until I can find a way to test for flicker. I will continue researching this topic and sharing my findings on this site.

If you have any additional information or questions on this, feel free to contact me on Twitter: @ShawnSeverinsen.

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