“Good night!” is “Доброй ночи!” (“Dobrai nochi!”) in Russian. TV-hosts started using this phrase on late-night TV. Then it became popular everywhere. This phrase is used to greet a person during a phone conversation. Also it’s a way to bid farewell in a friendly way before going to bed. “Good night!” can be translated like “Спокойной ночи!” (“Spakoynai nochi!”). So “Доброй ночи!” is an analog of this phrase. English-speaking people say “Good night!” when bidding farewell. But you should say “Доброй ночи!”as a greeting.