How can you use F.Lux on "Ubuntu 14.04.3 LTS" ?
please step for step an in easy words, because 1) my english ist bad 2) i don't really know how to use Ubuntu in general
gerne auf deutsch
Install that by following the instructions here: https://wiki.winehq.org/Ubuntu I'm not sure if they'll translate or work as is, but if you run into trouble, here would not be the place to ask for help with installing Wine.
Once wine is installed, install f.lux just like you would on a windows computer and download the .exe file.