What’s the Deal with Screen PWM?

What’s up nerds? Joe here to interrupt your Switch 2 hype with the most “boring” yet important article you’ll be reading for the next 5 minutes. That’s right, we are tackling Pulse Width Modulation (or PWM)!

“My eyes!” – Fred, the fish

Ever notice a bizarre flicker as you turn down your screen’s brightness? Do you get eyestrain staring at your 50% brightness monitor all day? Do you just want to delve into the exciting world of electronic signal regulation and why it matters? What is even the difference between PWM and a standard refresh rate?

We will answer that and more in an easily digestible manner that will leave you questioning your reality. YES!

Pulse. Width. Modulation…What?

In short, pulse width modulation is simply the deliberate staggering of electronic signals (Pulse) at a measurable distance (width) that controls the manner in which something behaves (modulation). Think of it like visualizing a heartbeat on a monitor, which also has a pulse. Man, waves are just everywhere, eh?

And like a wave, these too are measured in “Hz” (or hertz). Sounding familiar to another important metric? More on that later. Anyways, these “hertz” waves are measured in sequences of peaks and valleys known as “duty cycles.”

Duty cycles are measured like refresh rates at per second intervals with percentages corresponding to the amount that the signal is “on” in a given pulse. Pulse Width Modulation!

So…Screens?

Dramatic PWM duty cycle via rtings.com

Yes, so PWM is a very common backlight dimming method in TVs, monitors, and your favorite handheld consoles. PWM uses screen flickering to give the impression that your screen is dimmer.

For example: A 50% duty cycle means the backlight is on 50% of the time in a given cycle, giving you the impression your screen is at 50% brightness when in reality, it is actually essentially turning off and on an unfathomable number of times.

So, like Patrick Star rapidly turning on and off a lamp while chanting “Life. Death. Life. Death” about 650 times a second.

PWM vs. Refresh Rate

The Steam Deck OLED has a maximum 90hz refresh rate and a ~350hz duty cycle

Kind of obvious at this point, but these two aren’t the same and are controlled by totally different systems. Refresh Rate is the rate at which an image refreshes on your screen, which is most commonly 60Hz, or 60 times a second. Other common refresh rates are 120Hz, 144Hz and 90Hz (you get the picture).

PWM, however, is expected to flicker at rates so high a human eye can’t detect them. Monitor analysis media company Rtings.com pinned this number at 650Hz and above to be comfortable and unnoticeable, while also recommending panels with a PWM divisible by 60 so it fits evenly in a 60Hz refresh rate window.

These two systems work symbiotically to make sure you enjoy binging the Twilight series ironically (for my wife, unironically) at evenly paced frames that don’t make your brain hurt even more than it already does. Genius!

Getting PWNed by PWM

Russ from Retro Game Corps reported low PWM in his review of the Miyoo Flip

Human perception of screen flicker can be subjective and varies from person to person. But notably low frequencies of screen flicker can put strain on your eyes and noggin, or as claimed in a study conducted by Danish lighting company, Dial, on LEDs “…it can nevertheless have effects on our neurological system…because the optic nerve and the cortex can detect stimuli up to 160Hz, depending on modulation and wave form.”

Which just means that subconsciously, even though our eyes can’t detect it, our brains are working overtime to make sense of what you’re looking at. Notably, the Steam Deck LCD version has a PWM of about 450Hz, which is above the noticeable threshold at 50% brightness but can cause eyestrain in long intervals.

Additionally, what about when flickering is noticeable? Hopefully we remember the woes of the Retroid Pocket 4 and its low brightness flickering, and now the Miyoo Flip. That is actually due to the screen’s low PWM value, which was probably around 300Hz (just an educated guess). At low brightness, say 10%, the duty cycle is also at 10%, which in a low Hz duty cycle means your image is puttering along to maintain a 10% brightness.

Although PWM is not exactly a widespread issue, that hasn’t stopped some custom firmware developers from trying to help alleviate headaches. Just one example of this is OnionOS v4.3, which introduced the option to manually adjust the PWM frequency on compatible handhelds

How to Tell What Has PWM

Good question. One of the truly unfortunate aspects of PWMs is the lack of public awareness and the even higher lack of companies’ transparency regarding their screens. I can’t exactly blame them since this is generally overlooked from a consumer standpoint.

That being said…maybe they should. At the very least, declare what dimming option the device uses, whether it’s direct current, PWM, or straight up magic. Since this can be used in any screen type (OLED, IPS, etc) research is the key here.

While there isn’t a free resource out there to measure PWM in our favorite handhelds, I use rtings.com for TVs and monitors. Ritngs tests and reports on multitudes of different screens in a multitude of manners and include a dedicated section for flickering and PWM dimming at different rates of brightness. This will at least give you a semblance of what is considered a good or bad duty cycle.

Hopefully this is helpful for you screen warriors out there (or at the very least entertaining). Ok, back to Switch 2 hype!

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