Yosemite’s Dark Mode is a nice way to darken your screen a bit so it isn’t as bright, but you have to dig into the System Preferences to enable or disable it. Redditor abspam3 figured out a way to do that with a keyboard shortcut.
All you need to do is open up Terminal and type this in:
sudo defaults write /Library/Preferences/.GlobalPreferences.plist _HIEnableThemeSwitchHotKey -bool true
Then, log out and back in again. Once you’re logged back in, you can enable Dark Mode by tapping CTRL+OPT+CMD+T.