Actually, pretty much all digital to analog converters use PWM In order to adjust the brightness, you need to either get a different voltage (which would require complicated electronics and also result in several steps of brightness instead of freely adjustable slider) or use PWM. In the latter case, it’s important to know that the higher the frequency is, the harder it is to notice the flicker. For example, CRTs used 50Hz or a similar value as their refresh rate, depending on the region they were made for. Essentially, their refresh rate was their flicker rate because they would only light up once per frame. It is tiring to look at a CRT, but it’s already hardly noticeable. Now, modern LCDs flicker in many times higher frequency so it really isn’t noticeable and doesn’t cause nearly as much eye strain. When using my prototype I didn’t notice any discomfort. My desktop monitor, for example, does cause a headache after a full day of using it, but V didn’t do that. Except when I (foolishly) used it at full brightness. It’s really too bright.
You have managed to mix 3 different things together. CRTs used a higher refresh rate than regular LCDs use, but despite the higher refresh rate the effect was unpleasant due to the fact that the CRT image was created pixel after pixel, so a horizontal frequency was added to the mix. LCDs display the whole picture at once, so a LCD common panels refreshes at 60 Hz. PWM started to be an issue with LED backlights as LEDs are very fast in changing from on to off (so it is more of a shock to the eye) as compared with tube base backlight because that was slower in stopping to emit light, so the transition was softer.
PWM in the Vs display may be a valid concern as we have a quite strong/bright backlight, which means that for usual use you wont be running the backlight at 100 %. Now, the negative effect of PWM gets worse the longer the off cycle is, so the lower you set the brightness. And as said with Vs backlight be so bright, using it far below 100% will be common.
I agree with @Lbtv here that we should get the specs from the engineers. @Mike
Well, CRTs did refresh the image 50 times a second. Yes, LCDs do refresh it at 60Hz, but if we’re talking of PWM brightness regulation, we’re talking about a much more frequent refresh without actually updating the image. It just blinks the backlight many times per frame to reduce brightness.
That is true, but as I said, the faster that flicker is, the lesser the problem
Well, I was talking about really old CRTs… Those that used the electric distribution’s frequency as their clock. Like, in Europe we have 220V/50Hz in the US it’s 60Hz…
Anyway, my point is that not all PWM is bad. And there is no other way to change brightness, at least that I know of… Just take a look at this as an example: http://www.ergpower.com/pdf30/dimming_options.pdf
Analog dimming is possible, but do we want a potentiometer knob sticking out of our Vs?
As I said, the higher frequency they use, the shorter the non-lit “gaps” become so they’re harder to notice. I don’t have any numbers specifically about V’s display, but PWM shouldn’t inherently be interpreted as “bad”.
DC voltage control maybe. But that’s effectively using the same power as the display on 100% and just makes the energy that doesn’t go into brightness become heat. Not a solution for mobile systems if you ask me and I doubt Lenovo thinks this is the way to go either.
AFAIK there are no freely adjustable voltage regulators between 100 different levels (for each percentage)… I might be wrong though… It’s quite easy to implement it with PWM though, you just calculate the on/off intervals required to achieve the brightness you need.
If you’re referring to the table where the Miix doesn’t have a value for PWM frequency I’m guessing they just don’t have that data, the space below is also blank. I’d be quite surprised if it doesn’t use PWM and intrigued what they use instead
People are often misusing the PWM term. They just use it to describe tiring flickering, or one visible with bare eyes. In reality, pretty much all monitors use PWM and nobody really has a problem with that, as long as the frequency is high enough.