Eye Strain from LED Backlighting in MacBook Pro (2008)
discussions.apple.com
discussions.apple.com
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")
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.
Yes, I just added information about that to my comment, sorry for the race condition.
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.
[0] Bulb is not really an accurate term here. Maybe bulb-replacement?
I'm wondering if the Iris approach affects color accuracy, otherwise why wouldn't MS/Apple use the same technique?
PWM backlighting was introduced on the iPhone X and is affecting some customers.
edit: s/backlighting/OLED dimming/
At any level of brightness, modulation with a frequency of approximately 60 or 240 Hz is present ... It can be seen that the amplitude of the modulation is not very large at the maximum and near to it brightness, as a result there is no visible flicker. However, with a strong decrease in brightness, modulation appears with a large relative amplitude, its presence can already be seen in the test for the presence of a stroboscopic effect or simply with rapid eye movement. Depending on the individual sensitivity, such flicker can cause increased fatigue."
[1] https://translate.google.com/translate?act=url&depth=2&hl=en...
The flickering on this LEDs is not really any different from the CCFL flickers before.
CCFL PWM flicker: https://youtube.com/watch?v=RHlvgo6b_2s
LED PWM flicker: https://youtube.com/watch?v=84OCOX9O3PE
I...... I am very glad I'm using a CCFL laptop. This is like going back to evil 60Hz CRT flicker!!
I've just accepted I might need to rip out the LED driver board in a future laptop and replace it with my own design. Hopefully not, but if that has to happen then okay.
Thanks for the reference to the comparison, that was also very interesting to go through (and bookmark).
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.
> 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.
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.
I haven't tracked the cause down yet - I know it's a nerve issue of some kind - but sometimes my jaw, arms or eyes (yup) can occasionally jump. My jaw and arms jump when I'm nervous (or have a buildup of too much nervous energy/excitement), while my eyes jump when I'm trying to focus on something too hard, they drift, and I try to course-correct too hard. (I think half my brain is aware of the drifting, but the other half, the part that would make the fine motor movements to keep my eyes locked, is happily whistling away blithely in a corner somewhere.)
When my eyes jump and I overcorrect when I fail to re-point them where they need to be, I usually have a second or two where I'm not technically blind but I need to let my eyes refocus and remember their purpose in life (if you will) :P
I always thought this was nystagmus (read the term online one day and went "!!! that's what it's called!")... but now I wonder, is what I'm dealing with something else?
(An aside: I'm really, really bad at tracking moving objects in space. If someone else is holding onto something and I'm expected to look at it, I have to hold it instead. No other alternative.)
* BLF A6 (AKA Astrolux S1)
* Astrolux S41/Manker E14
* BLF X5/X6 (AKA Astrolux S2/S3/SS)
* Emisar D4, D1, D1S
* BLF Q8
* BLF GT
* Convoy S2+/C8 (new firmware version)
These don't all use the same firmware, but they all use an open-source firmware with high-frequency PWM, except that I think the BLF GT does not use PWM. A number of expensive custom lights use these too; those often focus on metalworking and exotic materials.
Firmware sources available here: http://bazaar.launchpad.net/~toykeeper/flashlight-firmware/t...
I own an Astrolux S41 (Nichia 219B), Astrolux SS (3A) and a semi-custom light I assembled using the A6 and Biscotti firmwares by ToyKeeper. I plan to pick up the Emisar D4 (Nichia 219C) and D1S (5D).
What does this mean? I would assume the surface brightness of the emitters is a good bit higher than that. Aside from surface brightness, lux does not provide any information about a light source without a distance. The SI unit of luminous flux is the lumen, and luminous intensity, the candela.
I have a Viltrox panel with similar characteristics, but smaller (adjustable color temperature, CRI 95+) and I think it uses 5mm Yujis. Brightness adjustment is non-PWM. It's also meant to take a camera battery, but I converted it to use two loose 18650s. Model VL162T, $30ish on Amazon.
Lux is lumens per square meter. Candela is lumens per steradian, the SI unit of solid angle. At one meter, these are equal, unless the beam hasn't converged at 1 meter. Aputure provides the beam angle in degrees, for which it was surprisingly hard to find the conversion. Sure, the units aren't technically comparable, but we know they meant the apex plane angle, at least we do now that I looked up the correct term.
So a right circular cone (which the light produced by a rectangular panel isn't, but we'll pretend) with an apex plane angle of 25 degrees has a solid angle of 0.1489365798 sr, approximately. 4380 lm/sr / 0.1489365798 sr = 29408 lm.
And that can't be right because the power consumption is 30 W, and the theoretical limit of luminous efficacy is 683 lm/W. I'd expect an LED panel like this to be on the order of 100 lm/W for about 3000 lm from 30 W.
As someone who knows zero about electronics fundamentals... how is this done?
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.
> 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.
The way you wrote this makes it sound like SMPS don't have the smooth progression linear regulators do, which is in line with what I understand about SMPS designs. I presume the controller is connected to (or incorporates?) a digipot or similar, or is it actually possible to define an arbitrary reference voltage (derived from a digipot for example)?
> 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.
Sure thing. And yeah, I find the constant-{voltage,current} thing a very fascinating/interesting quirk of LED regulation. At some point I'll find out why LEDs need constant current.
Switchmode supplies can output any voltage, they're not limited to discrete steps. Their only disadvantages are increased complexity and potentially increased output noise, depending on the design. Most good switchmode control chips use a bandgap voltage reference internally, that provides a temperature-independent fixed voltage. Then an internal error amplifier and some feedback from the output is used to control the output voltage. Think of it like a thermostat: if the output voltage is too low/high, the supply senses that and starts boosting/dropping the output. Once the output goes over/under the threshold the boosting/dropping stops, and the output starts to fall/rise. The supply keeps switching it around the output threshold. (Linear regulators do exactly the same thing, they just only drop the voltage instead of being able to boost, drop, or both. They also drop the voltage in a less efficient but less noisy manner.)
I see. So set the current, let it draw the voltage it wants. Heh.
> Switchmode supplies can output any voltage, they're not limited to discrete steps.
Right - the issue I was getting at was the problem of getting an arbitrary representation of a desired voltage out of a microprocessor and into the real world. Digipots are the only way I'm aware of to do that (apart from PWM).
Thanks for the very interesting and highly informative wall of text :)
Open question, in case this piques your curiosity: I'm very interested what your comments might be on https://news.ycombinator.com/item?id=15005811, and any suggestions/ideas you might happen to have. I've long thought that what I describe in this post is noise-related, SMPS noise in particular, but I'm absolutely stumped on how to pinpoint/narrow things down any further.
Edit: also to get a given voltage out of a microprocessor, you just use an analog-to-digital converter (ADC). Some have them built in, others are external. I like the AD9850 for hobby work, as it has a high resolution and is quite fast. If you need a large voltage range there are ADCs available for that, or you can amplify the signal from a lower voltage one.
WRT your issues with sensitivity to SMPS, it probably is audible noise. See if Screen Tunes[3] causes symptoms, it causes audible (but quiet) coil whine of varying frequency on most monitors I've tried. Your issues are unlikely to be directly caused by RF EM, but the side effects of the systems that generate such signals are often detectable by people.
[1] http://cds.linear.com/docs/en/datasheet/3574f.pdf [2] http://mmcircuit.com/understand-rcc-smps/ [3] https://thume.ca/screentunes/
> At some point I'll find out why LEDs need constant current.
There are flashlights that work by connecting a Li-ion battery to an LED through a FET that can use PWM to dim it. This will deliver all the power the battery is capable of providing at a given point on the LED's forward voltage curve. If that sounds like a good way to burn out components, it... can be. Everything needs to be fairly robust.
These flashlights do not have constant brightness. Even in lower modes, output tracks battery voltage. Strictly speaking, however, it demonstrates that it's possible to operate LEDs without constant current. Forward voltage drops a bit as temperature increases though, so LEDs are "greedy" and will essentially take all the current available as long as there's sufficient voltage. At some point, this will let the magic smoke out.
FET drivers in flashlights only work because the voltage range of the battery and LED overlap, battery voltage sags when it gets a heavy load on it, and some LEDs can handle a lot more current than the datasheet says for a few minutes at a time. None of these things are valid for mains-powered lighting, except that with sufficient heatsinking, many LEDs can be overdriven at a modest cost to longevity.
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.
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.
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.
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.
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.
Over the years I've used many different models too.
It's really not at all clear that they possess some kind of higher clock rate for sampling optical images.
I can deal for a few minutes, they have to live there!
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)
https://forums.macrumors.com/threads/eye-strain-while-using-...
It is, however often easier in terms of circuit design.
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.
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.
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.