A character enters a location, and it's dark. The first course of action is to switch on a light, be it from an actual lightswitch on a wall or one's portable light source. And... Surprise! In the room is an unexpected sight. Perhaps the character is in a lot of danger now, or at least some trouble. Or maybe it's just a Surprise Party.
This trope covers a situation in which a reveal of somebody's presence is made by turning on a light. Supertrope to Matchlight Danger Revelation, which involves going to a dark location and revealing danger via a lit match. The surprise might be part of a Caught Coming Home Late situation: someone waits — often in the dark — for another who's coming home past curfew.
If a light isn't turned on but a character is revealed as they walk out of the dark, it's Emerging from the Shadows. A dangerous entity waiting in the dark for someone in that person's own home who only wants to speak with them is Trespassing to Talk.
- Always the Quiet Ones: When the Rainbooms enter Fluttershy's room, they find it looks the same. Then when Applejack flicks on the light switch, it's revealed that the entire room is actually trashed.
- Casino Royale (2006) re-introduces James Bond in this fashion; he's waiting in a darkened office for his current target and only revealed when said target switches on a light to reveal that Bond has been in his safe:
James Bond: M doesn't really mind you earning a little money on the side, Croydon. She'd just prefer it if it wasn't selling secrets.
- Madman: The alcoholic Dippy finds out that his bottle of Jack Daniels is empty, so he gets up and goes to a door. When he turns on the light, he finds Marz waiting there. Marz then slices open Dippy's throat with his fingernails and drags the body away.
- A Cure for Wellness. Lockhart hides from the orderlies searching for him in a dark room, and lights a Cigarette of Anxiety. The lighter reveals something strange about the room, so he turns oh the lights to find it's full of bodies floating in tanks.
- The Fredric Brown short story "Nightmare in Yellow": The main character is coming home from work on his birthday and decides to start a new life, starting with killing his wife. He does so on the front porch when she comes out to greet him, then steps inside propping up her body, turns on the light and... all the birthday guests shout, "SURPRISE!"
- Teen Wolf: A frequent occurrence in Scott's bedroom in the first two seasons. Initially, it's Derek waiting in Scott's chair for Scott to turn on the lights, but eventually Gerard, Isaac, and even Scott manage to surprise someone coming into Scott's bedroom by waiting patiently in the dark.
- On Titus, Christopher Titus describes a surprise party they threw for his uncle. When he walks in the door and the lights go on and people start yelling, he draws a revolver and starts shooting, injuring at least one guest. He then realizes what's happening and says "You guys."
- The Defenders 2017: In "Take Shelter", when Matt drops by the Bulletin to grab Karen and move her into police protection, he announces his presence by turning on a desk lamp at the cubicle outside her office door, getting her to look up from her work.
- In Clock Tower 2, one of ScissorMan's encounters at the library has him surprising Helen in a water tank once she turned on the light switch.
- Five Nights at Freddy's 2: New to the game is that you can now turn on the lights in areas of the restaurant to check out dark spots. Needless to say, you're going to find some unpleasant things wandering around from time to time, and some details change depending on whether or not the lights are on, such as the animatronics on the Show Stage opening their eyes when the light in the eponymous room is turned on.
- One random event in Miitopia has lights switch off on an adventurer. After choosing which direction to go, the lights switch back on to reveal a surprise, ranging from a Surprise Party to tripping over a food item, to other party members having a moment.
- The short Switch is built around this trope. A young man is dropped into a small darkened room and all he can find is the switch for a unseen overhead light. Whenever he turns on the light, the room might be empty... or there might be a huge monster growling at him. Or there might be a mass of tentacles there. Or a pretty girl in a bikini. Or... eyes.. The empty room is boring and the pretty girl keeps turning the light off, if you're wondering why he doesn't stay on one of those two.
- In the My Little Pony: Friendship is Magic episode "Student Counsel", Trixie is so fed up with Starlight skipping out on preparations for the party that she summons Starlight to her office with the lights out, surprising Starlight when she turns the lights on to find Trixie sitting on the couch glaring daggers at her.
Starlight: Trixie? What are you doing here?
Trixie: It's the one place I knew I could find you!
- Extreme Ghostbusters: In "Back in the Saddle (Part 1)," Egon and Janine return to HQ after celebrating his birthday. It's dark, and an ethereal voice calls his name. He wonders if it's some vengeful spirit for a moment, flips the switch, and... IT'S PETER, WINSTON, AND RAY!