Twinkle Tray lets you easily manage the brightness levels of multiple monitors. Even though Windows 10 is capable of adjusting the backlight on most monitors, it typically doesn't support external monitors.
CareUEyes is a very simple but useful program when it is about your eye care. The program comes with a very simple and clean interface and needs to technical knowledge. Even a novice computer user can download and use it easily.
Allows to set the brightness (and other settings) of the monitor through DDC/CI. Meaning: keyboard and/mouse instead of having to fiddle with the OSD menu manually. http://www.lg.com/us/support/monitors.