This may only be for Dells, but I have that option under Control Panel, Power Options, Change Plan Settings, Change advanced power settings, Display, Dimmed display brightness. Please note, however, that even though the setting allows you to enter a value from 0-100%, 0% is not actually completely black, but rather just is the dimmest end of the available range, which may not actually seem that dim to you (it doesn't to me). I know of no way to modify the lower limit of the range.