Eye Strain from LED Backlighting in MacBook Pro (2008)

https://discussions.apple.com/thread/1677617

by walterbell • 9 years ago

69 90 9 years ago

discussions.apple.com

dmitrygr• 9 years ago

My research into LED
technology turned up
the fact that it is a
bit of a technological
challenge to dim an LED.

This is complete nonsense. While pwm can indeed be used, many of the nicer LED drivers are actually variable current. While adjusting the voltage directly indeed does not work as expected for LEDs, a constant current driver does indeed produce a constant brightness. Varying the current varies the brightness. Only the cheapest displays and lighting installations use pwm for brightness control.

modeless• 9 years ago

... and many car/truck taillights. I think PWM taillights should be illegal. The artifacts are distracting.

ChadMoran• 9 years ago

This, so much this.

I have nystagmus which means my eyes move uncontrollably. Primarily on the horizontal plane. While my brian compensates for this and I don't see a moving image anything that uses PWD flickers very, very badly.

PWM tail lights are THE ABSOLUTE WORST for this condition. Not only do I see it on the source but I see it on anything the light projects onto, it's horrible.

ScottBurson• 9 years ago

If not banned outright, they should at least be required to use a 1MHz minimum frequency.

exikyut9• 9 years ago

I've long wondered how this is actually done electronically. The only approach I've ever been able to come up with is a digipot connected to a linear power supply, but that would generate a bit of heat at low brightness settings, and I suspect even a 256-step digipot would exhibit visible fade "jumps".

As someone who knows zero about electronics fundamentals... how is this done?

Zak12• 9 years ago

Linear regulators are fairly common in flashlight drivers. They do generate waste heat at low output levels since the difference between battery voltage and LED forward voltage is just burned off, but the heat itself isn't a significant problem. Efficiency is more of an issue, but low-output runtime in LED flashlights is so long that most people will be able to charge their battery long before it runs out.

Switch-mode power supplies are the high-end version. These can step the input voltage up or down to produce the required output voltage and can regulate current to one or many desired levels.

More information on how both of these work is easy to find with a google search, but I should note that some things written about linear regulators assume a target voltage. When used to drive LEDs, regulators with a target current are required.

Zak12• 9 years ago

Worse than typical PWM is running LEDs from AC mains power directly. I've seen this used in large, high-output panels. 20,000 lumens with 50/60 Hz flicker is rather unpleasant to be around.

And yes, two other ways to dim an LED are a switch-mode power supply with output current regulation, or a variable linear regulator. I'm familiar with both approaches being used in flashlight drivers, though PWM is also quite common. Good PWM designs tend to be over 10 kHz, which is nearly always invisible to the naked eye.

jdietrich• 9 years ago

The 2008 MBP did use PWM backlighting. PWM is slightly more efficient than a constant current regulator and gives a more consistent backlight color temperature. IIRC Apple have stuck with PWM backlighting for these reasons, but have moved to an extremely high frequency (~120kHz) which should be imperceptible even to the most sensitive users. Many other top-tier laptop manufacturers also use PWM backlighting, but with a switching frequency of around 1kHz.

geofft• 9 years ago

Title should have (2008). (Also is there some current relevance that I'm just out of the loop on?)

ebbv3• 9 years ago

Nope, as far as I can see there is no reason for this to get posted. Seems almost like OP is trolling for karma because it has a controversial title and links to Apple.com.

walterbell11• 9 years ago

The thread is 164 pages long and active through 2017.

sctb• 9 years ago

Thanks! Updated.

sschueller• 9 years ago

Interesting, but don't CCFLs also "flicker" just at a much higher rate?

exikyut9• 9 years ago

Yes; I can see the flickering on my CCFL-based ThinkPad, but it's thankfully not annoying.

walterbell11• 9 years ago

Detailed comparison of CCFL & LED flicker: https://www.infobyte.hr/blog/134/ccfl-vs-led-screen-backligh...

CCFL PWM flicker: https://youtube.com/watch?v=RHlvgo6b_2s

LED PWM flicker: https://youtube.com/watch?v=84OCOX9O3PE

twobyfour• 9 years ago

It's evident that this sensitivity is pretty rare. But with essentially everything LED-backlit these days, living with that sensitivity sounds hellish!

KirinDave3• 9 years ago

Most people can see these effects if they know how to look for them. Most "sensitives" are folks who accidentally figured out how to see them.

It's really not at all clear that they possess some kind of higher clock rate for sampling optical images.

exikyut9• 9 years ago

I agree (I replied to the other comment in this subthread).

wlesieutre• 9 years ago

I've noticed this with some LED light fixtures in people's houses before and deliberately don't mention it because once you see it you can't unsee it. Particularly evident on things like running water in a bathroom.

I can deal for a few minutes, they have to live there!

exikyut9• 9 years ago

I can stare at my CCFL ThinkPad all day, but if I stare away from it at around 75-80° (basically not quite 90°, so say around 2PM on a clock) I can see it flickering away. But if I stare straight-on it's fine; it feels completely steady, and certainly more rock-solid than any CRT.

My light emits a (very) tiny amount of light when it's initially turned off. If I stare straight at it I can't see this tiny bit of light at all; I can only see it in my periphery. I suspect my inability to see flickering works by the same mechanism - and I'm very glad for that!

Incidentally, when I was using CRTs I had to have them at 85Hz to hide the flickering as much as possible. 60Hz would drive me nuts - but then again, I used 60Hz for several years while using MS-DOS, so I think 85Hz was just a strong preference.

This may be interesting to some: https://news.ycombinator.com/item?id=15004608#15005811 (the whole thread, along with the highlighted comment)

notadoc• 9 years ago

Not sure about the backlighting or a post from 2008, but on the topic of eye strain... the diminutive text sizes and obsession with low contrast throughout the redesigned bleached UI certainly causes me eye strain. I've heard similar complaints from others, and about the new system fonts and anti-aliasing too.

exikyut9• 9 years ago

I wonder if turning on accessibility features would help.

NateyJay• 9 years ago

The PWM backlight driver frequency should be much higher. This kind of effect is only perceptible at sub-kilohertz LED switching. The LEDs themselves are happy to be cycled into the megahertz, so the only reason for this on the Macbook is poor electronic design. A low frequency does provide reduced cost, slightly higher efficiency, and reduced auditory/RF noise emissions, but visual effect has to be top priority.

monochromatic5• 9 years ago

Yep. I wonder if you give up some small amount of power efficiency at higher frequency, but it shouldn’t be much.

nukeop• 9 years ago

Apple displays are always poor quality.

KirinDave3• 9 years ago

To be honest, I'm skeptical that this is a universal feature of the MacBook line. I don't own one of my own (I'd never!) but I use one for work and I can see those effects as well if I know how to look at them (I used to have a DLP and it was easy to reproduce the rainbow effect).

The flickering on this LEDs is not really any different from the CCFL flickers before.

pflanze4• 9 years ago

I think this probably concerns many more people than are aware of it. I could live with the flickering but I live better by doing what OP did, set screen brightness to max, on all of my laptops and external LCD screens. I then use redshift (I'm on Linux)[1] to dim the screen to the desired brightness, i.e. absorb the excess light in the liquid crystal layer. Sadly this does appear to lead to some loss in brilliance and color quality, but it's not too bad, and I like that I never have to see the flickering.

I know someone who puts a foil based filter in front of the screen, that may work somewhat better, I still haven't tried that myself.

I find it frustrating how almost all LED lighting installed in the UK is PWM based (if dimmed), or otherwise flickering (AC), too. And it's just a question of consumer expectation: if you buy an LED light bulb in a standard shop in Switzerland, it doesn't flicker, if you buy one in the UK, it does. Both bulbs use the new LED filaments, you can't tell the difference from looking at the bulbs, the difference is in how the power supply in the base of the bulb works. I opened up one of the Swiss bulbs and it had a proper switched-mode power supply (using a switching frequency probably in the 100 KHz range); I saw a video on Youtube by someone who opened up one of the UK ones, and the power supply was based on current limiting via capacitors (and then a rectifier), which leads to a flicker at twice the AC frequency (hence 100 Hz). There's going to be a cost difference of £1 or so, the Swiss consumers are apparently ready to pay for that, the UK population not (or the UK shops possibly pocket the savings).

[1] https://en.wikipedia.org/wiki/Redshift_(software) (actually still using the command-line variant of an older version, e.g. "redshift -b 1 -g 0.9:0.9:0.9 -l $POS -t 5500:4800")

Zak12• 9 years ago

A lot of cheap mains-powered LEDs aren't using PWM, but running on mains power directly.

You can test whether this is the case using a smartphone camera and an app with manual shutter speed control. If you see scanlines just above and below, but not at 1/50s, your light source is flickering at 50 Hz, which is the AC frequency of UK mains power.

pflanze4• 9 years ago

A lot of cheap mains-powered LEDs aren't using PWM, but running on mains power directly.

Yes, I just added information about that to my comment, sorry for the race condition.

yardie• 9 years ago

Could this be a difference in the dimmer. I’m in the US (120V vs 240V) and I had research carefully what dimmers were compatible with the dimmable LEDs in our flat. Sometimes the dimmer would hum, the LEDs would squeal, or they would go from 0 to 100% with 20% dimming.

Most LEDs are made in China and I doubt the Swiss are getting a specially manufactured ones. But old, incompatible dimmers are definitely a thing.

pflanze4• 9 years ago

No external dimmers were involved. As I wrote, I opened up a bulb myself (sawed off the tip of the base) and saw electronic parts consistent with a switch mode power supply (dozens of parts including rectifier, capacitor, tiny transformer, rectifier, capacitor, IC for controlling it). I know I saw something different than was in the video for the UK version! No reason China can't produce both.

Zak12• 9 years ago

It's not the LEDs themselves that are a problem there, but the driver circuitry in the "bulb"[0]. There are a fair number of these being made in the US and Europe, not just China. Significant numbers of LEDs are also made outside China - Cree manufactures LEDs in both the US and China; Nichia manufactures LEDs in Japan.

[0] Bulb is not really an accurate term here. Maybe bulb-replacement?

walterbell11• 9 years ago

Iris claims to perform brightness adjustments in software (GPU?), allowing the monitor’s PWM brightness to stay at 100%, for Win/Mac/Linux: https://iristech.co/iris/

I'm wondering if the Iris approach affects color accuracy, otherwise why wouldn't MS/Apple use the same technique?

systoll2• 9 years ago

The Iris approach lowers the device’s battery life, and the screen’s contrast ratio.

gm-conspiracy• 9 years ago

I find newer cars' brake lights at night very annoying with their PWM "trails".

amelius2• 9 years ago

Isn't the solution to simply turn up the frequency of the flickering?

Zak12• 9 years ago

That would be a solution, however flicker-free dimming for LEDs is not difficult. Linear regulator chips are cheap, but inefficient. Switch-mode power supplies cost a little more. Both are mature technologies any electrical engineer should be familiar with.

amelius2• 9 years ago

Now that you make me think a little deeper about it, it seems simple indeed. The exponential V/I curve of the LED makes I unstable for a given value of V, so all you need to do is have a feedback loop that controls I.

monochromatic5• 9 years ago

LED light output isn’t linear in power input though. PWM allows you to drive the LED in its most efficient regime no matter how much brightness you want.

alt_f42• 9 years ago

It is high time for an OLED dispay on the MacBook Pro. And not just on that horrible touchbar gimmick.

dijit• 9 years ago

OLED has horrible burn in. For phones they’re doing incredible mitigations but the fact is that the screen isn’t on with static elements for 8hours+ solid each day.

duckfruit• 9 years ago

I'm not so sure that's true. The mitigations they're doing seems to work very well for all sorts of form factors. I've been using a dell UP3017Q OLED monitor as my main display for most of last year and haven't had any issues so far whatsoever. It's simply the best display I've ever used. Even for my LG OLED tv, which I've had for a couple of years hasn't exhibited any image retention issues at all, despite watching a lot of news with scrolling headlines and logos. I wish OLED monitors would become more generally available since they're far, far superior to LCDs but for some reason apart from a limited run of the Dells and some short lived laptop models they're pretty much nonexistent.

mchahn• 9 years ago

the screen isn’t on with static elements for 8 hours

I have two old cellphones mounted on the wall in my house that show time, weather, control the thermostat, etc. Most of the display is static. After a couple of years the burn-in is dramatic. I was surprised as I thought only phosphors burned.

Stratoscope• 9 years ago

I can attest to the OLED burn-in. My three-year-old Samsung Note 4 has a very noticeable bar across the top, from the dark status line above what is usually a light background on everything else. I guess the rest of the screen is what is burnt in and the status bar area is closer to its original state.

I don't notice it most of the time, but it really stands out on anything full screen. I think I would be rather annoyed if a three-year-old laptop did this.

rayiner2• 9 years ago

OLED has worse PWM.

pflanze4• 9 years ago

It depends: I've got a Samsung S II with OLED and it doesn't show any flickering. But also a later Samsung also with OLED from all I can tell, and it does, and sat together with someone else trying to figure out what's going on. My interpretation is that early OLED displays were always running 100% duty cycle, but instead would lower the current through each pixel for lowering the brightness (when dimming the S II very low (and adapt your eyes), you can start seeing artifacts, i.e. pixels being lit up less precise because they are in fact using the lowest few values available of the current range). For later phones it appears Samsung added a PWM on top of it, so as to be able to dim the display independent of the pixel currents, perhaps to get rid of these artifacts in low brightness settings, or possibly because this might be a bit more power efficient.

What can be done, apparently (as my friend found out searching the internet), if you've got root, is to install a kernel driver to set the PWM duty cycle to 100% and instead use the old per-pixel dimming approach. I haven't bothered (not using my phones enough) but something potentially worthwhile to do if you use your device for a lot of (book) reading.

7ewis• 9 years ago

I use a MacBook Pro all day at work, then at home in the evenings. I can't say I've ever had an issue with eye strain.

Over the years I've used many different models too.

IdontRememberIt• 9 years ago

To manually check if the PWM has a low frequency: put your finger in front of the screen (or the led lamp you want to test), and move it quickly to describe a paper fan (V). If you see a stroboscopic effect, the frequency is too low. => The screen is not flicker free or the screen brightness too low. This is only a quick test not a bullet proof solution.

antirez• 9 years ago

Just tested my Macbook Pro (2016 model) with a 120 FPS camera and apparently there is no flickering in the display, however the keyboard backlight appears to use PWM.

systoll2• 9 years ago

Same for 2017.

I think a lot of it is down to the usage scenario, but the keyboard is the most obvious ‘flickerer’ I’ve seen... anywhere.

A screen like that [or a mandatory keyboard backlight] would be an instant dealbreaker to me.

derefr• 9 years ago

Question: this is a problem because the LED array (as an LED backlight or an OLED display is) all flickers in synchrony, right? Would it still be a problem if each LED in the array was hooked up to its own delay line with a randomized-at-the-factory value?

monochromatic5• 9 years ago

That would probably help some. Really, they should just flicker faster. There’s no reason not to do PWM at a kHz or 10, and nobody is going to see that flickering.

CamperBob2• 9 years ago

Actually, there is a slight problem, in that many people will be able to hear the inverter.

It's tough to make a completely silent inverter that works near the peak of human hearing sensitivity. It can be done, but it's likely to be more expensive.

Going all the way to 20 kHz+ is probably the best strategy. LEDs can be driven well into the MHz range, but if you go too high, RF emissions compliance starts to become a problem.

noncoml2• 9 years ago

Not sure if it is the OLED, but after switching from iPhone 7 to iPhone X I get terrible headaches when trying to watch Netflix on my phone before I go to sleep.

walterbell11• 9 years ago

It's a similar issue. The Samsung display in iPhone X flickers at 60/240Hz due to PWM brightness control of the OLED. This is more noticeable to the human eye at low brightness. Options are to use the device at higher brightness level or switch to iPhone 8.

https://forums.macrumors.com/threads/eye-strain-while-using-...

https://news.ycombinator.com/item?id=16088173

noncoml2• 9 years ago

It explains it, thanks. It’s a deal breaker for me so if I could I would go back to 8plus.

gargravarr• 9 years ago

This is something I noticed as well - I upgraded from a PowerBook G3 to a PowerBook G4 in 2009, and then to a MacBook Pro in 2010. I bought the fastest non-unibody machine available, a 2.6GHz A1260. It lasted me very well, five years of daily use before I upgraded. However, I began to notice the backlight issue. I'm a writer in my spare time, so staring at a screen is an occupational hazard. With a CCFL screen, I can stare at it all day at a comfortable level. With an LED screen, full brightness is astonishingly bright, so you have no choice but to use it dimmed. I found I could only go an hour or two at a time in front of my expensive MBP, and for a long time I couldn't figure out what it was. I considered going back to the G4 many times.

It was only after I started using an LED-backlit external screen that I spotted the connection. Apparently I'm a little more sensitive to PWM than average, although perhaps not as much as the OP of the Apple thread. At worst, after about 45 minutes, my expensive LED-lit monitor would give me migraines when dimmed, which the laptop didn't.

Either LED technology has improved or I'm no longer sensitive to it, because my current Clevo laptop is LED (as is just about every screen on the market now) and I'm okay using it for long periods. I had to learn to tolerate the external screen on maximum brightness in a well-lit room for a long time.

It's annoying and certainly not ideal, but I can't blame the manufacturers. CCFLs are power-hungry and toxic, and were always going to lose against LEDs. The technology is easily superior but lacks finesse. It only affects a minority of people, which is probably why it quickly supplanted CCFL - either no study picked it up, or it was such a small number that it could be ignored. I wouldn't want to keep using CCFLs but I wish they'd figured out a better solution before bringing LEDs to market.

ksec• 9 years ago

I wish there is a Standard where ALL LED, doesn't matter whether they are used in lighting, backlight, keyboard or what ever, small or big, to be flicker free. Or Extreme High Frequency.

There are increasingly more shops, shopping mall, or whatever places it is, and Monitor, billboard etc, especially in China or made in China where culture are more price sensitive, using cheaper LED, so they could say they are governmentally friendly. ( There are also some government incentive in doing so ). And INSANE environmental groups which forces everyone to switch to LED.

Many of these LED has flickering issues, that some people dont have a problem, some people are little annoyed but are fine with it, or some minority like me which needs to run away or I would puke or sick.*

I tired LED lighting once, it started have flickering issues two years in. It was very minor, but enough to irritate me. I have since switch back to good old light bulb.

*I have also discovered those who are sensitive to these flickering issues are also likely to be latency sensitive, as discussed in the computer IO latency and web latency.

pathartl• 9 years ago

I've always found LED Christmas lights to be the worst offender here. Most of the time this issue can be solved by buying quality LED bulbs and using the correct dimmer, if you have one.

Walmart had 100-bulb LED Christmas lights on sale for $6 a string. This is just around the price of non-LED strings, however these are 120v rated LEDs that run right off the mains with only a fuse to protect them. Needless to say these things are tied to the 60hz phase. Since these were being put on my tree this year, I decided to do something about it. A simple full bridge rectifier fixed most of the issue. I think now the phase on the string is more around 120hz which is much easier on the eyes.

I can still see the flicker, however it's not nearly as bad. I believe the thing that would fully rectify the issue (see what I did there) would be to throw a capacitor in the circuit to further smooth out the DC supply. Really it comes down to the idea of a diode; current flows in one direction. In an AC circuit, it flows both directions. Convert it to DC and smooth the supply out and you're using just as much energy without flicker. Of course this ends up costing more if the manufacturer were to implement, so there's that.

I really just want DC throughout the house.

RichardHeart• 9 years ago

https://www.notebookcheck.net/ always tests for PWM and otherwise has the best laptop reviews on the planet. Example of PWM test: https://www.notebookcheck.net/Lenovo-ThinkPad-X1-Carbon-2017...

Eye Strain from LED Backlighting in MacBook Pro (2008)

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