BrightnessTray is a free, portable app to change your laptop's brightness on the fly as well as turn off the display.
We tested BrightnessTray on our desktops, and for some reason, sure enough, it does not work. That seems like a shame that its only for laptops but regardless, the app is small, uses little resources, and is simple to use. All you need to do is click the tray icon and slide the bar to the desired brightness.
Right-clicking on the tray icon gives you the options to power off the display, enter sleep mode, turn on caffeine (spelled wrong in the app) mode, autostart and close.
Power off the laptop screen, and any connected monitors if possible.
Sleep mode shortcut.
Enable 'Caffeine' mode to keep the monitor from turning off during idle.
Enable 'Autostart' to put a shortcut in the startup folder.
If you find the need to change your brightness level frequently, then BrightnessTray is an excellent choice.