Personally, I'd type "TURN OFF LANTERN". (Also allow "TURN LANTERN OFF", at least so that pronouns work as expected.)
I also suggest "SWITCH LANTERN", which will turn the lantern on or off, as appropriate.
Other phrasings I've seen: "EXTINGUISH LANTERN", "UNLIGHT LANTERN".
Bloodhounds can make you laugh and cuss in the same breath. They are endearing, faithful, and can sling drool ten feet in any direction. -- Virginia Lanier