Can PWM - ALWAYS - be detected in video reviews?

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jeff51
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Can PWM - ALWAYS - be detected in video reviews?

Are Video Reviews a good indicator of Pulse Wave Modulation artifacts?
I sometimes see PWM in flashlight reviews on YouTube. Sometimes the reviewer comments on them – Sometimes not.
“I don’t see them” or “they are not noticeable” Is often followed by:
“Look how bright this is – Wow! – Amazing!”

I want to see if the presence or absence of PWM artifacts in a video reflects what the light might look like in real life.

A Quick PWM talk
Pulse Wave Modulation is used in many flashlights to control brightness.
Basically the LED is turned on and off very quickly.
The frequency of the PWM is how often the LED cycles On and Off per second.
The Duty Cycle is how much time (%) the LED stays on during the On/Off cycle.
The higher the Duty Cycle – the brighter the light.
Hopefully all this takes place so fast the user is not aware of it.

Unfortunately, not all lights are well designed.
Crappy PWM can lead to eyestrain, headaches, and even nausea.

I made a PWM generator that allows the Frequency and Duty Cycle to be set wherever I like.
I shot some clips of different lights and the generator output to see, well, what could be seen (or Not).
The camera I used is an iPhone. (With a little help from GORT)
PWM in videos is seen as a series of light and dark bands moving across the screen.

My Conclusion.
A light with poor PWM characteristics will not always be detected in a video.
Conversely, a light with PWM that is satisfactory in real life, may show artifacts in a video.
The second case is less likely but it can happen.

Using a sensor and oscilloscope, PWM can be measured. But without testing, it’s hard to determine what PWM characteristics are acceptable.
Using a moving object is a good indicator way to determine if the PWM character will be tolerable.
I’m working test to see if I can quantify that.
All, The Best,
Jeff

kennybobby
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What circuit did you end up using for your PWM generator?

Now i used to think that i was cool,
drivin' around on fossil fuel,
until i saw what i was doin',
was drivin' down the road to ruin. --JT

jeff51
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kennybobby wrote:
What circuit did you end up using for your PWM generator?

I ended up with a cheapo square wave generator from Amazon. 2 for $14. I think it’s mostly used to generate a signal for stepper motors.
1Hz to 150K, 1% to 100% Duty Cycle. It’s not real happy at the top end, but seems Ok in the Audio realm. It needs like 6v+.
Buttons to run up and down the values. Kind of a pain to control in the dark.
I tried a cheapo buck voltage dingus. Couldn’t keep the LED controlled very well.
So I used a buck converter with current control to drop the voltage so I wouldn’t fry the LED.

Geeze it’s amazing what a few bucks will get you these days. Where were all these toys when I was growing up and playing with electronics?
Oh, Well, at least I have fond memories of tubes glowing in the dark.
All the Best,
Jeff