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