It’s not the blue emitting light that causes eyestrain on OLEDs, it’s the low frequency pwm used to control brightness. Basically all the pixels turn on and off a few hundred times a second, not slow enough for your brain to consciously notice it, but fast enough for your eyes to react to what is in effect a strobelight right in front of your face. That is how dimming works on an OLED.
You end up with devices that still cause headaches and dizziness because they flicker in this manner, but are “eyesafe certified” because they filter out the blue light right before bed.
That got me thinking: couldn’t that be solved by adding a layer in fron akin to a phosphor screen which “buffers” the light a bit thus bridging the switching which should reduce flickering?
Not without losing brightness. White LEDs work that way and are less bright than an uncovered LED of the same power. Some of the light from the LED becomes waste heat instead of light when the phosphor absorbs it.
Also, not without losing response time. Part of the point of using LEDs for displays is that they can change brightness very quickly.
That’s a good point, I don’t remember much ghosting on those. I guess it might depend on the phosphor used. If it was tuned to only fluoresce for that imperceptible off time and no longer it would probably work.
I guess it’s a similar idea to quantum dots, but if those quantum dots fluoresced for just a bit longer.
Why is the pulse width so large? LEDs can toggle millions of times per second, not merely hundreds.
It is possible, by the way, to dim an LED without PWM the old-fashioned way: by varying the voltage of the power supplied to it (“DC dimming”). You can see this in devices that have an indicator LED that stays on for a few moments after power is disconnected, then fade out. What’s happening there is a capacitor in the device is (briefly) powering the LED. As its charge depletes, the voltage drops, and the LED dims. However, controlling LED brightness this way is a great deal less accurate than PWM, creating color distortion at low brightness. See related Android Police article.
I wonder if the problem with DC dimming could be solved by adjusting the voltage supplied to each LED based on measurements made in the factory of its brightness at different voltages?
It’s not the blue emitting light that causes eyestrain on OLEDs, it’s the low frequency pwm used to control brightness. Basically all the pixels turn on and off a few hundred times a second, not slow enough for your brain to consciously notice it, but fast enough for your eyes to react to what is in effect a strobelight right in front of your face. That is how dimming works on an OLED.
You end up with devices that still cause headaches and dizziness because they flicker in this manner, but are “eyesafe certified” because they filter out the blue light right before bed.
OLED TVs and desktop monitors don’t use pwm, though they do have very slight brightness dips every refresh.
Afaik laptop and phone OLEDs do use (low frequency) pwm.
That got me thinking: couldn’t that be solved by adding a layer in fron akin to a phosphor screen which “buffers” the light a bit thus bridging the switching which should reduce flickering?
Not without losing brightness. White LEDs work that way and are less bright than an uncovered LED of the same power. Some of the light from the LED becomes waste heat instead of light when the phosphor absorbs it.
Also, not without losing response time. Part of the point of using LEDs for displays is that they can change brightness very quickly.
I think this would result in some pretty intense ghosting and other undesirable artifacts.
Ghosting on CRTs wasn’t too bad, mostly imperceptible even
That’s a good point, I don’t remember much ghosting on those. I guess it might depend on the phosphor used. If it was tuned to only fluoresce for that imperceptible off time and no longer it would probably work.
I guess it’s a similar idea to quantum dots, but if those quantum dots fluoresced for just a bit longer.
Eventually, there will something like a 1000 Hz monitor. At some point, it will refresh too fast for the brain to register any difference.
Fuck PWM, all my homies hate PWM
Why is the pulse width so large? LEDs can toggle millions of times per second, not merely hundreds.
It is possible, by the way, to dim an LED without PWM the old-fashioned way: by varying the voltage of the power supplied to it (“DC dimming”). You can see this in devices that have an indicator LED that stays on for a few moments after power is disconnected, then fade out. What’s happening there is a capacitor in the device is (briefly) powering the LED. As its charge depletes, the voltage drops, and the LED dims. However, controlling LED brightness this way is a great deal less accurate than PWM, creating color distortion at low brightness. See related Android Police article.
I wonder if the problem with DC dimming could be solved by adjusting the voltage supplied to each LED based on measurements made in the factory of its brightness at different voltages?