It’s clear that you haven’t really looked much into this. It’s per pixel.
Screen protectors also degrade light output
Screen protectors also degrade light output
So does this function from Samsung. You can see in all the video demonstrations that the 'privacy' pixels are notably dimmer even head-on compared to normal pixels.
These pixels are dimmer by themselfs. They dont get muted by a layer on top of them.
This means way less energy usage therefore longer lasting battery at similar brightness!