I would like to put Red-light on if no VPN connection is active in my phone. I think the problem is not about choosing the best VPN application here to make VPN connection, but about to find an application which finds if VPN connection is active and affects the front-light of the phone.
Phone: Samsung Galaxy S4 gt-i9506
System: CyanogenMod 13, Temasek's unofficial ROM with patches
VPN client: NordVPN