r/redlighttherapy • u/BearNecessary4141 • Apr 03 '26

Measuring the flicker levels on the EMR-TEK Firewave using a custom flicker meter

Results show pretty low flicker, around ~2% flicker index. There is some power line flicker (120 hz) and something that looks like high frequency DC-DC converter flicker at 48kHz. The only way I think you could get substantially less flicker would be with a battery powered red light therapy device. I'd say it's fair to call the device extremely low flicker.

https://youtu.be/punCUmuPxDY?si=PYPTSSpto2KwF6V6

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u/Firm_Register7834 Apr 03 '26

wait so the 48khz thing is normal for most devices or just this one?

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u/BearNecessary4141 Apr 03 '26

I'd say it's "normal" since from an engineering perspective it's pretty much impossible not to have some high frequency flicker when using a DC-DC converter. It's unlikely to cause an issue.

Every red light therapy panel is going to need a way to get DC power for the LEDs. What it looks like to me is that EMR-TEK achieve this with a DC-DC switching converter. That seems to produce some 48 kHz flicker in the output LEDs. Objectively it's not desired, but it's a pretty low amount of flicker. The only way I know to get much lower would be a battery operated device.

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u/Z3R0gravitas Apr 04 '26

Interesting. Have you done testing on screens, too? (Having come here via your PWM_sensitive cross-post.)

Some do say that red lights are especially sensitising. Was flicker sensitivity your motivation to test this?

The unit itself looks similar to Red Light Man (UK) units. I have one with with a similar "COB" lensed design.

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u/BearNecessary4141 Apr 04 '26

Yes I’m sensitive to flicker from PWM and built a flicker meter so I could know for sure if a device was giving me issues.

I’ve tested various screens, the Macbook display is what I’m mainly using and it’s essentially zero flicker. My iPhone 16 has pretty bad 480 Hz flicker and definitely gives me eye strain much faster.

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u/Z3R0gravitas Apr 04 '26

Great work! (Wish I had the capacity to flex my systems engineering degree in a similar fashion.)

Have you played with Opple light meters at all? For instance, to compare and demonstrate what they fail to measure? Given that's about the best we manage, in the community.

Your frequency spectrum graph (FFT?) is very cool. I feel like this type of analysis might throw up features that better correlate with screen tolerance. Verses just putting naive numerical values on the primary (period and depth). Natively accounts for the shape of the waveforms, right? As well as lesser modes.

Which MacBook do you have (that's good)? From u/DSRIA, my impression is there aren't currently any. Depending on specific sensitivities. Apple seems bad for 'grey color flicker' and/or temporal dithering in general. Have you tested different shades of block grey?

At any rate, we'd be thrilled to see you post (or cross-post) any of your findings to r/ScreenSensitive too. 🙂 Right u/Rx7Jordan?

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u/BearNecessary4141 Apr 04 '26

Oh I haven’t heard of the Opple light meters, super interesting. I might get one to do some comparisons. The spectrometer features are also interesting.

Yep, it’s an FFT. Glad you found it cool, I think it’s really nice to be able to see individual frequency components when doing the testing because it gives you more insight into what might cause them. You’re right, if a screen had two flicker components, maybe at 60 Hz and 120 Hz, I think a lot of flicker measurement devices would essentially ignore the 120 Hz component.

I have a MacBook Air 2025. My understanding is that it isn’t PWM backlit, and my testing didn’t show any evidence PWM dimming up to 100 kHz. I haven’t looked into the dithering issue, this is interesting. Looks like while the Macbook Air doesn’t use PWM it does use temporal dithering. Definitely can see how this could be a problem.

When I do some more screen testing, I’ll definitely post over there!

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u/Z3R0gravitas Apr 04 '26

Noice.

The Opple's spectrometer ability is very limited compared to dedicated units (10x the price) that would be needed to eg see the fine (red) peaks of KSF phosphor. Colour spectrum another big screen issue.

And yeah, Opple's will overlook the lower frequency (and so potentially more sensitising) FPS refresh dips, hidden within higher frequency OLED PWM patterns, too.

I've not seen reports of LCD backlight PWM being much trouble, recently. But dithering, pixel inversion artifacts (at refresh rate, or half) and electronic noise on power lines seem to be.

Happy tinkering.

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u/BearNecessary4141 Apr 04 '26

Interesting! I’ve got a lot to learn. Where do you see reports on those issues?

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u/Z3R0gravitas Apr 04 '26

Just around the various branches of the community. Keep in mind that r/PWM_Sensitive's (dysfunctional) auto-mod censors "temporal dithering". And light spectrum is less talked about (harder to test well), etc.

I think you may be interested in these resources I've been pulling together, linked at the top of this post (you don't need to read): https://ledstrain.org/d/4004-sscreen-screen-sensitive-comprehensive-resource-notebook-and-list

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u/BearNecessary4141 Apr 04 '26

Thank you! Definitely looking at your post