Librem 5 Backlight PWM frequency

+1 but sometimes the internet is just too much …

That’s why, because of better contrast, I use Cobalt option (instead of Oblivion) on my gedit. I just wonder how would look option with some reddish font on the same black. And, “ambient light white-point matching” will not make my writing here better anyway.

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I’m (kind of) sorry but I disagree :wink:, as I’m sure you already knew (even if just subconsciously aware) that something has changed, but it was not you that changed. And, IMO, you are right on topic here. Older cars use tungsten halogen headlamps and as your eyes understand (see) difference they silently argue (migraine) or make some kind of protest when not pleased, against blue LED light “bites” that are usually well combined with harmful PWM glimmer. I would rather say that exactly this, noticing the difference between harmless looking at static pictures, like books you read or paintings you admire and the looking by exposure to the blue LED light combined with the poor PWM frequency, makes you expert on this field (because most of us don’t have quality “time” to notice this, and get the most expensive blue-light blocking glasses against such, but such glasses cannot improve bad cause/source and particularly not glimmer). Therefore just two advantages I currently think of about tungsten filament light bulbs as healthier option for our eyes:

  1. Color rendering index (CRI or Ra) of light was (because incandescent lamps are almost past time) 100%, same like our daily sunlight, without any glimmer which means zero or 0% of PWM (was not in use),
  2. Out of topic, but color temperature was up to 3000K and this was for decades purposely mandatory for night traffic (even though that the quantity of light (lux) was relatively small, in comparison with LED, but sufficient), until the blue LED was invented and awarded with Nobel Prize in Physics.

P.S. I might try to get OSRAM 2600K Fog Breaker Series light bulbs (I had some similar earlier) for my car because they are worth every cent when needed. It is just funny (to me) how some of the most expensive SUVs (homologation inclusive within EU) cannot drive more than 50 km/hour on country roads when fog is heavy, but who cares, mass production case. Let me make up why it is like this (the reason why): because they drive main LED headlights with color that is often more as 5000K and fog just returns white light like mirror. Topic borderline shows barely to me but I know is there (Am I still on the road? I see just fog and nothing else.).


here are some LED modules that are 98 CRI but very expensive > check the about page also …

led is energy efficient and it has that going for it … sure there are the ones that are really high powered but the luminous flux emitted is much higher compared to traditional lightning methods …

about glasses … my pair have anti-blue light treatment and they DO affect the perception of blue-light coming from the display-panel. it’s not an assumption i can very clearly see with my OWN eyes a DIFFERENCE by taking them on and off. This is funny because my ophthalmologist (link for younger audience - if there are any :stuck_out_tongue: ) said when i asked that it will NOT change my color perception. i suppose it’s pointless asking ( if it IS a filter it will change SOMETHING at least)


me too. but then again i’ve always found out vim or emacs to be preferable in terms of customisation :wink: (probably too much for just reading lol)

imo the darkest sepia color background with very light orange text - that any color monitor can correctly display - is the best choice in terms of contrast/eye-fatigue

true OLED would be nice to have on any Librem device but without the burn-in and the power consumption :stuck_out_tongue:

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Thanks! Your link to Beijing Yuji International Co., Ltd., my link above to Toshiba Materials Co., Ltd. TRI-R and this one to Seoul Semiconductor SunLike LED are links to the very same products. I’m currently using this light bulb from Yuji with 3000K.
Edit: is manufacturer page (without store.).


25,00 € tax excl. for that bulb seems acceptable to me if you compare to other similar price but not the same CRI specs. 10w for aprox 900 lumen is a little steep but it’s ok. but enough about Yuji LEDs - getting to far off-topic here …

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I think anyone who waits for the bus (never learned to drive, sad I know) at night can be considered an expert :frowning: Not only do you get assaulted by those insane xenon or whatever lights but also those flashy pulsing bicycle lights (which I actually agree with for cyclists safety, but they’re still way annoying!) The best solutions I’ve found so far is : always wear a baseball cap so I can lower my head and I too have to special coating on my glasses. That’s what helps a bit for real life, but for looking at a phone (which is more controlled) I wonder if there is a way to cancel out the glimmer (or at least change the Hz (?)) to something more reasonable by maybe adding to it somehow? (kinda like how white noise works?)

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As earlier stated from @dcz this is what we expect, nothing more and nothing less:


That’s great news :slight_smile: …annnnd I probably should have been paying closer attention :hushed: Ah well, I had a lovely Saturday because wondering about it led me to contemplate the old Battlestar Galactica viper helmets and then guess what I did today :smiley:

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I hope Dorota :smiley: too. Thankful I’m for sure, because I feel sure/confident that Purism team manages/avoids PWM on Librem 5 screen. Maybe I talk (or provoke) to much and not always fair, but how otherwise to know if someone is taking care of this (or not). Also, I still cannot say that I’m familiar with asking questions on forums.

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Tee hee, me neither! :slight_smile:

I look to context for ones motivation more than what is actually said, tactics used, etc. and I think most people do. I don’t think anyone here thinks you’ve joined “the mission to destroy” :slight_smile:

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OK, I have tested the screen on my Librem 5 Evergreen.

I could not detect any backlight flicker at all, at any brightness level, so I am happy to call the Librem 5’s screen “flicker free”!

I was able to detect the invisible infrared light from the proximity sensor to the left of the front camera, which flashes at roughly 200Hz with an extremely short duty cycle, whenever the screen is lit up. This stops happening when all three kill switches are turned off (for “lockdown mode”). After turning one or more of the kill switches back on again, the pulsing doesn’t resume until the next time the screen transitions from off to on. So, if the screen is already on, and stays on, then the proximity sensor doesn’t flash. (Not that I think anyone should be concerned about the proximity sensor’s flashing; I just thought it was interesting how it does that.)

I verified that my test set-up was able to pick up PWM backlight flicker from my laptop, with the laptop set to 200Hz, 2347.75Hz and 18750Hz. (My laptop’s backlight PWM frequency can be manipulated by altering the value in an Intel GPU register.)

I used a small solar panel comprised of two 4 x 7 cm solar cells connected in series, connected directly to the scope probe, with AC input coupling on the scope. The solar panel is a good fit for the size of the Librem 5’s screen.

I used the Librem 5’s default text editor program to provide a white screen and used Phosh’s top drop down thingy to adjust the brightness to various points throughout the slider. I didn’t use any particular precision when selecting brightness levels, because it’s a fumbly, finger-controlled thing, but I made sure I got the minimum and maximum brightness, and a good spread of points in between, with particular attention given to the low end, because some screens only use PWM at the low end of the brightness scale.

When testing the Librem 5’s screen, I was able to go down to 2mV/cm in the y axis without seeing any signal indicative of screen flicker. This was in sharp contrast to the laptop screen flicker, which was evident even at 2V/cm.


A bug maybe?

Pretty cool find overall though. I can confirm that the sensor is emitting IR light.

I wonder whether it could be used for an IR remote control.