Darkness Equals Death

"It is pitch black. You are likely to be eaten by a grue."

- Zork

If someone enters a dark space in any horror media (though action films also use the trope), you know something's going to happen, and it's not likely to be good. Something's going to snatch someone, burst into the room, be lit dramatically by a sudden flash of lightning, and/or bull rush the heroes.

Happens especially in rooms where there are dangly things to hide the villain. Foreboding Architecture and evil being badly lit tend to compound the problem. Bonus points if a storm causes the aforementioned lightning flashes. More bonus points if it's the attacker who set up the dark room in the first place.

Daylight Horror is Not a Subversion, but an inversion of this trope.

Films

 * Alien was full of these.
 * Iron Man has the sequence when Pepper goes into Section 16. Also the beginning, when the terrorists are searching for Iron Man right before the killing starts.
 * Jurassic Park has it with the raptors in the power station.
 * There's a good guy example in Batman Begins in the sequence on the docks, where Batman pulls a mob goon into said dark space.
 * And again in The Dark Knight, when he's interrogating the Joker.
 * The new I Am Legend, when Sam (the dog) follows a deer into a building.
 * It is the outright basic gimmick of Darkness Falls. The "tooth fairy", a ghost of a woman who was heavily burned in life, experiences extreme pain and can be eventually destroyed when exposed to light, but can essentially teleport anywhere else. The main character manages to survive his first encounter with the tooth fairy as a child, and then never goes into the darkness again until he's an adult.
 * Happens in Deep Blue Sea - female scientist goes into her dark, half-submerged room for files. A shark sneaks in and tries to kill her.
 * And then she strips down to her bra and panties. Talk about lighting up a room.
 * There's a very eerie scene in Cloverfield where the main characters are walking through some pitch black subway tunnels and hear... noises. The night vision setting on the camera provides a very nice HOLY SHIT moment.
 * During the failed operation to remove Octopus' tentacles in the second Spider-Man movie, a nurse is dragged screaming toward a dark area of the room.
 * Beautifully subverted in the movie Wait Until Dark. Audrey Hepburn plays a blind woman who knocks out all the lights to give herself the advantage over her attacker.
 * Too bad she forgot one.
 * Pitch Black was designed from the ground up to utilize this trope, and every single death in the movie did in one way or another.
 * The escape from Crematoria in the The Chronicles of Riddick sequel was also intended as a deliberate inversion. The world's surface is only cool enough to survive upon during the night. Naturally, circumstances conspire to force the protagonists to escape, on foot, by day.
 * Correction: the surface of Crematoria is lethal during both daylight and nighttime. It's only during a short window before sunrise that the surface is habitable.
 * Subverted in the 1980 movie version of The Shining where Jack kills  under the only lit lamp in the hall.
 * The Zombie Diaries has a group of survivors looking through an abandoned house where they enter a dark room and... Well you get the idea.
 * Subverted in Scream 2, where  is killed in broad daylight, and in the middle of a very active college campus. For everyone else in the series though, this trope very much applies.
 * Another Christian Bale example in Equilibrium: during the raid on the sense-offender's camp/base in the Nether, Grammaton Cleric Preston arranges for the power and light to the last pocket of resistance to be cut, bursting into the room just as it goes dark. After several seconds of gunfire intended for him, the room is completely dark, with the sense-offenders whisper to each other as to whether they got him. Then Preston opens up using his Gun Fu, illuminating himself and small other parts of the room with muzzle flash, wiping out the mooks. It's all very beautifully done.
 * A variation occurs in The Mist. Surely, at daytime the mist is not dark, but you still can't see that far in front of you..
 * The Descent takes place in an underground cave. So all over the characters, as well as the audience, could only see as much as their helmet lights and glow sticks could show. When they burn out... bad things happen.

Literature

 * In the book Firefight, written by Chris Ryan, the freedom fighter Faisal Ahmed disables the power in a country house, then once the SAS team leader goes to investigate, the other two men react too slow in the darkness and are slaughtered mercilessly.
 * H.P. Lovecraft's The Haunter of the Dark features a monster that can be hurt or banished by light, and which goes after the protagonist during a thunderstorm that knocks out the lights.
 * Every death in Dead Friend (aka The Ghost) happens on a dark night in a dark room. For an extra kicker, there's usually a storm outside too.
 * In Phantoms, you might as well sign your own death warrant before you go into the shadows. Not that being in the light makes you much safer, but at least you'll see what's about to eat your face.
 * Arguably the entire point of House of Leaves.
 * In Darkness Falls, the monster of the film hates going into the light. So when the lights go out in the area the characters are in, the monster attacks. And when the flashlights get lost...
 * Some critics have summarized the movie as ninety minutes of the cast running around chanting "Stay in the light!"
 * Several Fighting Fantasy books will award you non standard game overs for going into tunnels and caves without a light (many of which chastise the player for their foolishness). The Zork gamebook has you (unsurprisingly) eaten by a Grue.

Live-Action TV

 * Subverting this trope was the very reason why Joss Whedon created Buffy the Vampire Slayer: instead of having a blonde entering a dark corner and never coming back, you have a blonde entering a dark corner and coming back with a spinal cord in her hand.
 * He sets out his stall in the very first episode: a blonde girl goes into the school late at night with a boy - but as this blonde girl is really badass vampire Darla, the boy's the one who meets a sticky end.
 * Prominent in the episode "Bushwhacked" of Joss Whedon's Cult Classic show Firefly. The crew of Serenity come across a ship which has been attacked by and they explore its innards for potential salvage and survivors. They come across.
 * Doctor Who example: The new series episode Silence in the Library gives a rather literal example. "See, you were right to insist on a night light!"
 * Also, if you're seeing statues where they shouldn't be, you'd better be in daylight. Torches might help, but statues of the angelic bent have a nasty habit of switching them off in order to come and get you...
 * In The X-Files episode "Darkness Falls", the Monster of the Week is a swarm of flesh-eating bugs that only attack in the dark, making it crucial to keep the generator going.
 * Invoked in the Criminal Minds episode "Our Darkest Hour", where the killer's MO is that he strikes only in darkness by taking advantage of power cuts.

Videogames
"Rumia: Are you the kind of person I can eat?"
 * In Doom, a room suddenly turning dark indicates a monster ambush. While some enemies are visible in bright areas, darkness makes them practically invisible.
 * In Doom 3, a game infamous for this trope, there's a section where you have to choose between the flashlight or a weapon (unless you are escorting a scientist carrying a lantern.)
 * If a level is dark in Halo, it is likely that you will be fighting Flood very soon.
 * Subverted in Alone in The Dark, where the main characters randomly end up in a dark room lit only by the fire of their automatic guns; they wipe out the evil attempting to kill them. Those not in the darkness, in well lit areas, will end up dead by the end of the scene.
 * In Apollo Justice Ace Attorney's third case, employs the same tactic by running into a pitch black stage to take cover from an assailant.
 * Averted most of the time in Dead Space, many of the zombie monsters attack you in very brightly lit areas, allowing you to see them in their full horrifying glory (And making you jump all the more when they actually do attack you in the darkness).
 * Also, just because the lights go out, doesn't mean you're about to be attacked. In fact, it's a 50-50 chance.
 * Played more straight in Dead Space 2, where the Necromorphs are much less inclined to attack in bright areas, and much more inclined to attack in darkness.
 * Zork had a species of monsters called Grues, whose entire purpose was to pop out of nowhere and eat people who wandered around without a light. Earlier versions had Bottomless Pits instead, but it was pointed out that a lot of the bottomless pit locations made no sense; one was in the attic of a house that was otherwise perfectly intact.
 * The bottomless pits were brought back for the prequel, Zork Zero. The game's ending reveals that
 * In the Scott Adams text adventures, wandering around in the dark without any lighting for too many turns will cause you to trip and break your neck.
 * Shadowgate employed a similar gimmick, with two torches you needed to keep lit. If they went out, you'd stumble around in darkness until you fell and died.
 * In the Lost video game, in the cave level something would invariably stalk and kill you if you walked around long enough without a light source.
 * Explicitly used in Wii Ware game LIT. The objective is to cross the nearly pitch-black rooms of the school by creating paths of light with lamps, computer monitors, etc. Stepping into an unlit area is instant death.
 * Rumia, from Touhou.

"Nightcrawler Commander: We've lost six men to to the creatures in the shadows. Avoid the dark, if you can."
 * She is a subversion though, as she can't see in her own darkness.
 * Tumbling down a dark staircase by going in without a light source was one of the ways you could die in the Laura Bow series of adventure games.
 * Used very literally in the first Gears of War game. Whenever you entered a dark patch of the (outside) environment, the Kryll (a swarm of flesh-eating bats) would consume you in around three seconds. Thankfully this also worked on enemies, so you could shoot out lights above enemy positions and watch the carnage ensue.
 * Runescape has something similar, if you enter a dark area with no lightsource, you "hear the skittering of tiny insects on the floor" a few seconds later, and you will be hit with a constant stream of 1 damage every half second or so.(new players start with 10 hp, the best of the best have 99, to put that in context)
 * Parodied in the Interactive Fiction game Enlightenment, where the goal is
 * Spelunky's dark levels are one of the worst threats in the game, concealing enemies and traps in the shadows just beyond the Spelunker's tiny circle of light. Oh, and you have a limited supply of flares, which go out instantly if you touch water. Fortunately, the developer has mitigated this somewhat by making certain level features function as light sources.
 * In Minecraft (full version), being outside in the dark is a very bad ide-SSSSSSSSS *BOOM*. So is going into caverns without plenty of torches. The game mechanics make things spawn where it's dark, while (sun)light burns the less horrifying ones. And the developer is threatening to make torches non-permanent, so that you might watch them go out one by one around you. It's also suggested to sleep in a well-lit room so you wouldn't be woken up by a zombie.
 * Inverted in The Aether, where the most dangerous common mobs spawn in broad daylight, but none spawn underground except in the Dungeons, and even those spawns are Dungeon features rather than random monsters.
 * The developers of Mirrors Edge deliberately made lower areas darker than the sunlit rooftops.
 * Darkest Fear by Rovio Mobile is based on this trope; the puzzles all revolve around navigating your way around the shadows  by manipulating various light sources.
 * In Penumbra, there was a perfect example in which you had to run down a hall in which the lights were turning on and off. You had to ALWAYS be in the light, if you stepped into darkness, something launched out of the wall and ate you.
 * Much of the beginning of Half-Life 2: Episode One takes place entirely in the dark, with throngs of headcrab zombies everywhere and a Ten-Second Flashlight and very occasional flares as your only light. Even more terrifying, zombies spawn faster with the lights out!
 * Splinter Cell and similar stealth games are effectively a version of this trope, for all your enemies. In one level, the hero's helpers aid the hero in eliminating a squad of enemies by cutting the power. As the lights go out, the player quickly eliminates all the foes.
 * Implied in the First Encounter Assault Recon expansion pack Perseus Mandate, from what we hear from a recorded message. No light has any effect whatsoever on the supernatural creatures fought by the player, however.


 * The Darkness is an entity unto itself in Alan Wake. It possesses people and objects that can only be fought off by shining a light at it.
 * In King's Quest VI, when you fall into the lower level of the Catacombs, it is pitch black. You are likely to be eaten by the Minotaur if you don't produce a light quickly.
 * In Leisure Suit Larry, wandering into dark alleyways results in Larry getting beaten to death by a mugger.
 * Inversion: If you don't turn your flashlight off in the "We Can See in the Dark, Can You?" level of Pathways into Darkness, you will be constantly attacked by Goddamned Rats.
 * Silent Hill. "Don't be afraid of the dark. Be afraid of what it hides."
 * Inverted in Amnesia the Dark Descent. While staying out of the light too long will reduce your sanity, it is also the only place you are safe when being attacked by the monsters.
 * In Space Quest II, if you go into dark caves without a light source, you will be eaten by a Cave Beaver or Cave Squid.
 * Starcraft, Warcraft, and many other Real Time Strategy games have the Fog of War. Finagle's Law guarantees that if you run a unit into the Fog without looking ahead, it will get attacked.
 * The SNES Jurassic Park tie-in game had a primitive first-person mode which activated inside buildings. Wandering into a darkened space before obtaining the night-vision goggles meant a swift death, even if there were no dinosaurs inside once the player obtained the goggles.
 * The Ambridge Mansion series plays this trope to the hilt - something as simple as or  can get you ambushed.
 * Deja Vu 2: Wandering around the empty bar without a light could randomly kill your character.
 * The Legend of Kyrandia featured a segment that plays the trope quite literally. Just before the darkness, you have access to a bush full of glowing fruit. You have to carry the fruit with you through a maze of caves so as to light them. But they can only be carried through three rooms. Go into a fourth room, and they literally burn out. And if you're caught in one of the caves when it's pitch black, it's game over. You need to find another such bush within the maze to keep going. Gets a little tricky at points because you can be at the point where the next move burns out your fruit, so most players save just before then just in case they take the wrong turn.
 * In Sonic & Knuckles' Sandopolis Zone Act 2, you must keep the lights on to avoid being ambushed by ghosts.
 * One of the worlds in Kirby Mass Attack has levels that revolve around obtaining torches and use them to light candles and other appliances, and feature enemies that will kidnap your Kirbies easily, and can only be made vulnerable by exposing them to a light source.
 * Las Plagas in Resident Evil 4 are vulnerable to light, so Ganados are much weaker and can't release them from their bodies in the first part of the game, that takes place in broad daylight. Then first the sky is darkened by a rainstorm, and then night falls...
 * This happens to Brad, one of your allies in Dead Rising. A struggle between him and the main villian ends with him thrown into a pitch black maintenance tunnel. Crawling with thousands of the undead.
 * Averted (to an extent) in Mother 3, as
 * In Hydlide, if you enter a cave without the lantern, you will randomly die. And then, after getting the lantern, you see that there was nothing killing you.
 * Castlevania II: "What a horrible night to have a curse".
 * Dark areas in the Descent series often contain Demonic Spiders, especially the invisible type.

Western Animation

 * In Gargoyles: The Goliath Chronicles: The Dying of Light, a blind gargoyle from a recent surgery and a blind human employ this tactic against attacking Quarreymen. The villains decide to create their own light by crating a small fire.