TL;DR: Can a smartphone LCD screen burn in when emitting nearly no light, but just dark dimmed pixels? And could, by such way, a screen-on time of 8 hours be achieved?
I'm designing a concept that requires quick access (from lock screen to tap in app in 1 second) to a single function inside an app. Since the lock screen for users without TouchID takes quite some time, relatively, I thought to force the display to remain turned on. The app should be used during conference presentations and since some conferences are a full day of length most smartphones can't survive that long with the screen turned on.
To save the battery I thought of over-dimming the backlight/screen of the device and become lighter when used. It's an extension of the default dim functionality. But I was worried that
The screen might burn in when having the screen turned on for an hour using black pixels on LCD displays and non-transitioning graphics (like a screensaver).
Even by dimming the brightness to an extreme level, that might not extend the battery life to an 8-hour of constant-on screen time.
Since you don't need to see the screen actually, and actions are confirmed by vibrating, the screen could be dimmed extremely. Therefor I'm looking to confirm my thoughts.
Too bad you can't run an app in the background and execute actions from the lockscreen, multiple times, without unlocking the device. Neither widgets can, as far as I know.. That would solve the whole issue of being quickly accessible, turned on screens and saving battery life...
I wrote this, because I might be wrong and you might know an alternative.