Darkness is a vital tool to horror. Horror and the dark are so intertwined that the idea of watching horror tends to evoke any imagery related to darkness, from night skies to pitch-black shadows. It harkens back to a primal fear that afflicts many from a young age- nyctophobia. Nyctophobia is an irrational, extreme fear of the dark, and it leaves many children clamoring for a night light. Darkness is petrifying for most because it removes all visual stimuli and triggers the imagination. Who knows what threats may be lurking in the shadows. 

That’s why horror thrives in it. Just seeing a dim room in a horror movie puts you on edge as your mind immediately starts checking the perimeter for danger. Conversely, light brings safety. It shoos away the encroaching terror. This simple dichotomy makes for one of the genre’s most enduring motifs. Horror offers no shortage of creatures that thrive in the dark or monsters weakened by the light. Vampires reign supreme as one of the foundational movie monsters with a significant sun allergy, but the world of things that go bump in the night is vast.

The monsters in these horror movies will leave you sleeping with the lights on, from ghosts to aliens.

Darkness Falls – The Tooth Fairy

Matilda Dixon earned the nickname of the Tooth Fairy thanks to her reputation for giving children coins for their lost teeth. An accident left her disfigured and sensitive to light. Then the adoring town residents of Darkness Falls turned to skepticism and ire when two children went missing. They exposed her to light and hung her, erroneously. Matilda returned as a vengeful spirit, cursed to destroy any that look upon her. If you hadn’t guessed already, light proves key in stopping this shadow-loving ghost.  

Lights Out – Diana

David F. Sandberg’s feature debut expands upon his short film, giving its unsettling entity a backstory in this scare-heavy metaphor for depression. Teresa Palmer stars as Rebecca, a woman drawn into the mystery behind her young half-brother’s night terrors that leave him refusing to sleep at night. It turns out that their mother’s imaginary friend “Diana” is real, and she’s a deadly entity that physically manifests in the dark. That means that safety from Diana exists solely within the light, especially if their mother can no longer keep her at bay. Sandberg nails scare-crafting here. 

The Descent – Crawlers

One year after a tragic accident, Sarah sets off with her friends on a spelunking adventure. Too bad pal Juno leads the group into an uncharted cave system, which traps them due to a collapse. As if no hope of rescue isn’t bad enough, this cave system happens to be inhabited by man-eating creatures. The fight for survival has never been quite as primal and bloody as it is in Neil Marshall’s fantastic entry in the annals of claustrophobic horror. Deep within the bowels of a cave, the Crawlers long ago adapted to an unlit terrain where the sun can’t reach. These creatures hunt in darkness and never come out during the day.

Don’t Be Afraid of the Dark – Homunculi

After uncovering an old fireplace, Sally begins to hear eerie voices shortly after moving into an old mansion she’s inherited with her husband. She unwittingly set free little goblin-like homunculi that dwelled within, and they’re determined to make her one of them. Too bad no one believes Sally. She finds an ally in lights, which deter the tiny creatures. But it’s only temporary. The 2010 R-rated remake makes these creatures far more vicious tooth fairy-types, but the TV movie brings a quieter, more unsettling atmosphere.

The Monster – Monster

Ten-year-old Lizzy (Ella Ballentine) is tired of taking care of her out-of-control mother Kathy (Zoe Kazan) and demands that she be taken to live with dad straightaway. It’s the middle of the night, and Kathy crashes into a large animal in the middle of the road, leaving her injured, and the car stalled. The pair soon realizes they’re not alone; something is stalking in the woods and sees them as new prey. Mom and daughter don’t stand much of a chance against the giant, reptilian creature hunting them and anyone who crosses their path. The playing field evens out a bit with the discovery that the beast has a severe aversion to light and fire.

The Hallow – Fairies

This dark fairytale is part creature feature, part body horror, and all Irish folktale. Corin Hardy’s feature debut follows a British plant conservationist and his family as they discover the hard way what it means to ignore warning signs and invade the territory of fairies, banshees, and changelings. There’s nothing sweet or cute about these deadly creatures. As the beings descend upon his home and attempt to steal the baby, it becomes evident that one of the most significant assets in this fight for survival is light; the light repels them.  

Pitch Black – Bioraptors

After crash landing on a desert planet, the crew and passengers of a commercial freight ship soon discover why it’s been seemingly abandoned when a rare eclipse begins. As the world descends into complete, pitch-black darkness, underground aliens erupt onto the surface for a feeding frenzy. Survival will be extremely tough for humans. The sci-fi horror movie launched a Riddick (Vin Diesel) franchise, but the Bioraptors nearly upstaged him. These predatorial and often cannibalistic aliens’ only prominent vulnerability is photosensitivity. These aliens are built for ripping prey apart, and the sheer, overwhelming number of them on the attack makes them more deadly than anything else on this list, especially with so few places to hide.