I once spent a couple weeks living only by candlelight after 8:30 or so, no screens. It's hard not to get enough sleep that way. You can still read, play board games/cards, write, study, play or listen to music, prep/cook food, talk(!), and tons of other stuff, but go figure, those things don't tend to keep one from going to sleep at a reasonable hour (you may be surprised at what's a "reasonable hour" for you when literally far more total entertainment than was enjoyed over any entire given year in the Imperial capital of Rome isn't available at your fingertips).
Netflix, cable tv that's on 24/7 (not my thing, but lots of people use their TV that way), video games, news feeds, mindless browsing, "who was that one guy in that one thing? Hold on, I'll look it up", what's Trump up to now? (better check!), a few thousand lumens of artificial lighting after the sun goes down, and so on... you'll put off sleep for those, maybe without realizing it ("it's not like I even feel tired yet", sure, but you would if you hadn't been playing Playstation or watching Netflix or scrolling through Facebook in a bright room for 2 hours straight, and if you didn't have the option of doing the same or similar for another two hours)