joblack, thanks for the hack! Worked flawlessly. Great idea based on what geekmaster did here
Still, there was quite a drawback - once you put lighting off in cron, you won't be able to easily turn it on again (at least for more than a minute). Therefore I propose other solution:
* * * * * var=$(cat /sys/devices/system/fl_tps6116x/fl_tps6116x0/fl_intensity | grep -e '[0-9]'); if [ "$var" = "FrontLight(Intensity) = 1" ]; then echo -n 0 > /sys/devices/system/fl_tps6116x/fl_tps6116x0/fl_intensity; fi
Simply put it in crontable instead of joblack's code. Every minute it checks if the lighting is in the lowest setting available by kindle interface and if so, it turns the light off completely. But it won't do anything if the setting is other than the lowest. So you can easily use PW both with and without light with no need of further changes in crontable.