Adaptive brightness won't turn off

Hello,

TL;DR: I’ve tried everything to disable adaptive brightness with no luck. Any suggestions?

Recently I bought a Dell Inspiron 3542, built on the Intel i7-4510U with Intel HD4400 graphics and also an nVidia 840M. The laptop is running Win 8.1.

My problem is that, when the laptop is running on battery, I can’t disable adaptive brightness, no matter what I try.

* I have disabled adaptive brightness in the windows control panel, under advanced power plan settings.

* I have disabled adaptive brightness in Intel’s graphics control panel. Ditto for nVidia.

* I have disabled the Sensor Monitoring Service under windows services.

* I’ve even tried uninstalling Intel’s and nVidia’s drivers.

When the laptop is plugged in, there’s no adaptive brightness. When the laptop runs on batteries, adaptive brightness kicks in.

Of course the laptop’s drivers are updated to their latest versions. Even the BIOS is updated to the latest version.

I thought this would be a Windows problem, so I tried running Linux. Still the same. The screen will dynamically adjust its brightness. So it’s not a Windows issue. Maybe it’s the Intel driver exhibiting the same behavior on both OSes? (long shot)

Could it be the laptop screen has dynamic brightness built-in? Is there even such a thing for laptop screens? The screen is the LP156WHB-TPA1, made by LG Display Co. I’ve checked on the internet but can’t find any info on such a feature, if it exists.

Any help/ideas/suggestions with this issue will be most appreciated!

Thank you,

George