Backlight controls for your laptop to vary the brightness and even for your Desktop monitors (as long as you install ddcutil or libddcutil and your monitor supports DDC controls). Just place a backlight gadget in the shelf on each monitor you have and that gadget will control the backlight on that specific screen, allowing every screen to have a different level if you want. Be aware that DDC monitor control can be a bit unreliable especially when you try and control a monitor while it powers on or changes resolutions. This will vary from monitor to monitor.