PWM same with naked eye as with video camera?

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rickw12
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PWM same with naked eye as with video camera?

Another newbie question, this time about PWM.

I was ready to click the “buy” button to get a Nitecore Tiki when the matter of its PWM at low modes came to my attention. I looked at the video on Nitecore’s website and, sure enough, the PWM is obvious. As I read further about PWM, I read that it doesn’t appear the same to the naked eye as on video camera. Is that true? If so, maybe Nitecore’s video isn’t a good measure for actual use.

The reviewer on ZeroAir said the PWM on this light is terrible, but in his review all he shows are charts. When I said in a comment that I don’t know what that means for “real life,” he said to imagine a strobe light. Is it that bad?

About PWM, I also read this on another forum:

“It’s all about frequency. At about 60hz people can maybe detect it. Above that you are starting to switch faster than the rods and cones in your eyes can follow to where it is undetectable above about 100-200hz. If that is the case, there is no way for you to detect that there is any switching going on at all.”

I looked at the specs on the Tiki and didn’t see anything about Hertz. Is there a standard or a typical rating for LED flashlights?

Rick

MascaratumB
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I don’t know about the TIKI in naked eye, but using the RovyVon Aurora A8U that has PWM, I can tell you that in may situations you’ll notice it without a camera.

I don’t know about frequencies and stuff like that, I just know that in some cases, you’ll notice it (near falling water, when you shake the flashlight all of a sudden…) . Not if you’re staring at it while it’s still, but when it implies movement you’ll see it…

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mattlward
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I notice PWM when I move a light. If I am walking and the frequency is low, it gives me a sense of peripheral movement that is not there. Drives me nuts!

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hank
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One of the search terms you want is “flicker frequency” and note that people vary as individuals in their ability to see or not see flicker.

As with color temperature, you’ll find people opining universally based on their individual personal experience.

Here’s one paper:

https://ece.northeastern.edu/groups/power/lehman/Publications/Pub2010/20...

Quote:
The health effects of flicker can be divided into those that are the immediate result of a few seconds’ exposure, such as epileptic seizures, and those that are the less obvious result of long-term exposure, such as malaise, headaches and impaired visual performance. The former are associated with visible flicker, typically within the range ~3- ~70Hz, and the latter with invisible modulation of light at frequencies above those at which flicker is perceptible (invisible flicker). Human biological effects are a function of flicker frequency, modulation depth, brightness, lighting application, and several other factors. …

Here’s another:
https://www.graybar.com/applications/lighting/blog/the-flicker-checker-o...

Quote:
try an electronic flicker checker. You probably have one in your pocket! Pull out the digital camera on your smartphone and point it at the nearest light source. If you see a series of bars or stripes on your display, that source is flickering.
MascaratumB
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mattlward wrote:
I notice PWM when I move a light. If I am walking and the frequency is low, it gives me a sense of peripheral movement that is not there. Drives me nuts!

Yup, spot on! That’s precisely that Sick

[REVIEWS] ACEBEAM: H20 / TK16 /// AMUTORCH: S3 / S3 vs 219c / AM30 / AX1 / VG10 /// BLITZWOLF: BW-ET1 /// BRINYTE: T28 /// DQG: AA Slim Ti /// FIREFLIES: ROT66 GEN II /// HC-LIGHTS: SS AAA /// KLARUS: XT1C /// LIVARNOLUX: 314791 /// LUMINTOP: Tool AA V2.0 + Tool 25 /// NITEFOX: UT20 / ES10K / K3 /// ODEPRO: KL52 / B108 /// OLIGHT: M2R Warrior /// ON THE ROAD: M1 / i3 / M3 Pro /// ROVYVON: A2 + A5R / E300S / A8 /// SKILHUNT: M150 /// SOFIRN: SF14 + SP10A / SP32A / SP10B /// WUBEN: TO10R / E05 / T70 / E10 / TO50R / E19 /// XTAR: PB2 Charger /// Tricks: 1 / 2 / 3 / 4 / 5 / 6 / 7 / 8 /// TIR Lenses: 1 / 2 /// Others: Biscotti 3 + 1*7135 / Triple TIR w/ XP-G2 ///// My Collection ///// My Review's Blog (PT)

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rickw12
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Thanks for your comments. The lower two modes of the Tiki (1 and 15 lumens) I would likely use only briefly. If the next higher one, 60 lm, had noticeable PWM, that could be a problem.

Rick

Enderman
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PWM on a camera is not the same as with a real eye.
Most of the time it is a visible flicker to a camera but cannot be detected by humans.
There are some cases where PWM is low enough that it can be seen with a human eye.
So it depends on a case by case basis.

jon_slider
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rickw12 wrote:
The reviewer on ZeroAir said the PWM on this light is terrible,

Is it that bad?

I have not tried the Tiki
I do trust ZeroAir reviews

PWM is a somewhat complicated, and polarizing, topic.

I suggest you form your own personal opinion from direct experience, if you dont want to liste to ZeroAir.

my advice is, you have been warned

Im very concerned about PWM
but 50% of people are not…

I notice the PWM on modern LED taillight arrays.. it looks like the car is strobing and moving erratically
Im very sensitized to PWM, I spent a long time trying to find lights without it

It is true that what shows on camera may or may not be something you see in actual use
its a deep topic, if it interests you, buy a Tiki and let us know your impressions..

hank
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Quote:
In bright light, humans have a flicker fusion rate of about sixty flashes per second, but in birds it’s much higher, about one hundred per second. In fact, it may be even higher in birds like hawks, whose survival depends on speed and accuracy.

Flicker fusion rate affects how well you can see details while moving. Since birds have evolved to move at faster speeds than humans, a high flicker fusion frequency gives birds better visual acuity. When moving at high speeds, a bird can perceive and avoid obstacles in a fraction of the time that you could.

Human visual systems evolved to function best at walking and running speeds. However, when you get behind the wheel of a car, you move much faster, and unlike a bird, your visual system isn’t optimized for speed, so your ability to see obstacles decreases as your speed increases….


https://indianapublicmedia.org/amomentofscience/flicker-fusion-frequency...
Valynor
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> At about 60hz people can maybe detect it. Above that you are starting to switch faster than the rods and cones in your eyes can follow to where it is undetectable above about 100-200hz.

 

People are of course different but 100-200Hz is way too low. I can easily see 1000 Hz PWM out of the corner of my eye when the light moves fast. 

Flashlights like the Emisar series with ~15kHz PWM are flicker free for (almost?) everyone so from my personal experience I would say >10 kHz is a must because PWM is distracting and annoying.

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I see 60Hz flicker constantly. If it's something that moves it's beyond unacceptable. There's, to me, three aspects of flicker: 

  • Frequency
  • Duty cycle
  • Amplitude
    • By this I mean, what percentage of the output flickers? Many lights have a constant current component as well as a PWM at various output levels.

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hank
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https://duckduckgo.com/?q=flicker+peripheral+vision

https://biology.stackexchange.com/questions/31536/why-can-i-see-a-light-...

Evolution in action — when something’s approaching you from the side, you don’t need to know what color it is.

Enderman
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Seeing a discountinuous line when moving a light quickly is not the same as being able to see the led turning on and off when staying still.