Oh, and welcome to the BLF!
All the Best,
Jeff
That explains a lot, actually. All these years, I thought it was just K-mart in general having those effects on society.
I hope you enjoy your stay, Sombrero!
I guess that looking at the phone and monitor screens for several hours a day has a more negative impact on eyesight. This light also flickers very quickly.
Thanks for the kind greetings! 
I am new in this forum and the LED flashlight universe, I got my first serious led flashlight yesterday (Sofirn Q8 Pro), and I love it!
You all wrote interesting answers, but the conclusion is quite controversial for me. I think the main question is that how much the energy of a fast blinking light is “integrated” in the retina. A stupid example: If I push my finger to a 300 degree hot iron for 3 second, it will burn my skin. But if I touch it in very short impulses, It won’t hurt at all. But maybe the light exposure is not analog with my example.
kennybobby: No, I don’t (yet) use the light for therapy, but in the lowest brightness it has so faint light, that I can easily look directly into the LED chips. I tried this, after this I red a more technical review on net of my light, there turned out than the brightness level is implemented with PWM.
Sorry for my bad english…
Many PWM controlled lights have an additional channel running at a few hundred mA only. Quite safe if you don’t do silly experiments.
Kmart blue light specials - good one!!! 
no it does not
For those who are interested, I connected my oscilloscope to the Q8 Pro led cables, here is a GIF with some frames captured, from the minimum toward the maximum brightness:
what you want to know, would take an eye PhD to tell you
if they even know
wle
sorry but ALL ‘white’ LEDs use blue light to make the yellow that mixes to seem white
white isn;t white
that article barely says anything
wle
Here’s a video of the BLF LT1 lantern showing the various PWM and waveforms.
0.00: Middle Tint Setting, Ramping the Brightness. The PWM Duty Cycle reaches 54% Duty Cycle. On Low, the Frequency changes to 3.9kHz, with a very short Duty Cycle.
0.46: All cool LEDs only, Ramping the Brightness. Notice the light at full brightness has no PWM. It’s running a DC Offset. As the brightness decreases, the Duty Cycle lowers. The Frequency stays at 15.9kHz. At the lowest brightness, the PWM again drops to 3.9kHz.
1:40: A Middle Level Brightness setting, Ramping the Tint. Very unique PWM waveforms are created by the Duty Cycles of the 2 types of LEDs Interacting with each other.
2:15: Ramping both the Tint and Brightness.
I changed the time frame on the scope to zoom in on the waveforms. Starting at Warm, Low Brightness. Ramping to Full Brightness, Cool Tint.
Notice that at Full Brightness, the light is not running pure DC Offset.
There is still some Duty Cycle being seen from the LEDs.
I miss-spoke in the video. The full cool bright is a DC offset, but there is some artifact left from the way the Duty Cycles of the LEDs are interacting.
There are some really interesting waveforms being generated by the Duty Cycle of the warm and cool LEDs stacking on top of each other.
Taking a look at the ends of the tint ramp – The single square wave Duty Cycle, is (I assume) an indicator as to why some have reported that the light has the longest runtime when at those tint settings.
All the Best,
Jeff
That was really cool Jeff, thanks for sharing.
Where was the scope probe connected, or how was that signal generated/captured?
It’s probably about suppressing melatonin at night. Early studies involved nurses IIRC. There is something, but you cannot be sure it’s the light (alone).
Relevant information regarding flicker and its health effects can be found in the publication: IEEE 1789-2015.
The side effects, such as headaches, vary from person to person, but also vary depending on the brightness of the light, and the depth of the modulation. Dimmer light is less consequential.
There is a graph on page 29 which suggests that at 100% modulation, above 1150 Hz, the side effects go away.
Some people are prone to seizures from strobing light, but 100Hz is not that low, most old CRT TV screens operate at 24-30 FPS (Hz) and 60-120 Hz for monitors and modern TVs. In fact 50-60Hz was chosen for electricity because it would not affect humans when using appliances the oscillate with electricity.
All that said such a low PWM light makes for poor lighting where there is motion so no one would want it.
Wait until you find out how computer screens and smartphones work 
Yes, thanks.
I’ve banned green/blue-ish indoor ALAN. Even got a Google Nest Hub 2 to have an adaptive display minimizing blue light at night, and using now the C01R around the house. Excellent to not disturb wasps and hornets too much (other than reported, they see the shine of a red light, but to a much lesser degree than white light). For walking the dog I’m using 5000K.
I feel sorry for those night workers. Should be restricted to health and emergency things, but well, money makes the world go round :-(.
I am actually very curious to know how it works. But I find very technical videos about it.
I’ve been interested in PWM in lights for a while now. I’m really sensitive to PWM and wanted to be able to measure it without having to try to open up a light to make a connection. Not possible in many lights.
The scope was hooked to a simple circuit using an OSRAM photo diode.
This same diode is found in many LUX meters and seems very linear until it clips.
The circuit was based on the work of Terry Oregon in his thread about looking for a sensor with a fast enough response time to get a look at a flashlights LED characteristics.
Terry’s thread
My thread about my first version
I later ditched the filter - it was too big of a pain to use.
I added a longer tube over the sensor and controlled the light intensity by angling the tube relative to the flashlight beam.
For those wanting to explore PWM but without an O-Scope, I did a thread on using a computer sound card and free software to look at PWM.
It also has references to other PWM threads.
The worst PWM I’ve seen was a camping lantern from Amazon. .100Hz
On high the 100Hz PWM with about a 98% duty cycle was just fine. No problems at all.
On medium 100Hz with about a 66% duty cycle - it was very noticeable and not very nice.
On low, 100Hz and about a 5% duty cycle - just nasty. For me - instant eye strain with headache to follow.
Any eye movement gave the old-time movie flicker show.
PWM tolerance seems to vary a bunch. Some are not bothered at all, some (like me) are very sensitive.
There are several manufacturers that have surprisingly low PWM frequencies.
I’ve been experimenting with PWM trying to come up with some sort of “?” to equate to what is tolerable (at least for me).
I have come to the conclusion, it’s not the PWM frequency other than how it relates to the time the LED spends in the off part of the duty cycle.
Don’t really have any numbers yet. Got sidetracked and didn’t get back to the project.
I don’t think there are any health risks from the PWM itself (other than the above). Prolonged exposure could lead to nausea or in some individuals some sort of seizure related to the eye strain(?). But there is plenty of early warning for this.
It’s the 10Hz-20Hz region that is considered dangerous for those who have possible epileptic (Etc) problems (I believe).
All the Best,
Jeff