Comment 234 for bug 1303736

This solution works on my laptop (ubuntu 16.04, but should work on previous OS):
open as root file
/etc/UPower/UPower.conf
and change IgnoreLid=false ==> IgnoreLid=true
save changes, restart system and now it works :-)
You can remove light-locker now.

You can use bash for these:
sudo sed -i -e 's/IgnoreLid=false/IgnoreLid=true/g' /etc/UPower/UPower.conf
sudo apt-get remove --purge -y light-locker light-locker-settings
and restart system now