Small service tracking backlight state and restoring it on power change. This mean battery and AC have a separate brightness level and the same is restored once power state changes. Essentially the same thing for Ubuntu that the Windows already have.
Currently it only supports Intel cards.
wget -O- http://packages.medo64.com/keys/medo64.asc \
| sudo tee /etc/apt/trusted.gpg.d/medo64.asc
echo "deb http://packages.medo64.com/deb stable main" \
| sudo tee /etc/apt/sources.list.d/medo64.list
sudo apt-get update
sudo apt-get install backlight-tracergit clone https://github.com/Medo64/BacklightTracer.git