Treehouse of Fun doesn't have any wiring installed, so you'll need something else to light things up. Lanterns are a dangerous alternative for your Arboreal Abode, so we can't use any old candle...
How about we just shove some fireflies into a jar?
Maybe a Nature Spirit is more comfortable with a paper lantern of glowing bugs than a wrought iron lamp burning some oil. Or maybe some Beetle Maniac thinks that Biotech Is Better. Whatever reason for it, the idea of using lightning bugs or glowworms to see feels closer to nature than a burning wick of wax. Sometimes, it's a result of nature itself and not someone's Bug Catching: perhaps a grove will light up when a swarm of shimmering butterflies resting on the walls rustle their wings.
There's some Truth in Television, but only as a fun activity for little kids, as they're tiny, short-lived bugs that only glow at a certain time of day during a select period of the year; you'll need to constantly resupply the jar with food for the bugs (and in some species, the adults don't eat at all); it will take dozens of them to make a feasible light source.
A Sub-Trope of Fantastic Light Source and Bioluminescence Is Cool. A Sister Trope to Glowing Flora, where a plant is used for lighting. Overlaps with Bamboo Technology and Bug Catching, and rarely with Fairy in a Bottle.
The trope name is a Pun on "lightning bug", which is an alternative name for fireflies. Not to be confused for when moths swarm around a lamp or when light acts wonky in a video game. Also not to be confused with Thunder Beetle, where the "lightning" in "lightning bug" is literal (but you could still put it in a jar anyways).
- Grave of the Fireflies: Realistically portrayed — as the film's title forebodes, the firefly lamp is short-lived.
- A Bug's Life: Swarms of fireflies work as a myriad of fixtures across the bug city: resting on bent nails for street lamps, flying between hollow Christmas lights for traffic signals, wearing aluminum skirts to make spotlights, etc.
- The Ant Bully has Zok's firefly companion, Spindle.
- Despicable Me: Briefly used as a gag when one Minion uses another as a glowstick, bending his cylindrical body to make him glow.
- Atlantis: The Lost Empire: The Atlanteans use round, hollow orbs hung from poles and filled with glowing insects for illumination. Notably, the insects they use for this role are the same kind that earlier destroyed the expedition's campsite, as they burst into blazing flames when crushed.
- Disney Fairies: In Tinker Bell and the Lost Treasure, Tink's Snarky Non Human Side Kick, Blaze the firefly, embodies this trope in the poorly lit parts of their adventure.
- Robin Hood (1973): A fishbowl of fireflies hung from a fishing pole is used as a way to trick Prince John into thinking that Robin Hood (disguised as a Romani fortuneteller) can speak to spirits.
- In Hedgehog in the Fog, the Hedgehog briefly uses a lightning bug sitting on a stick to light his way through the fog and try to find the pot of jam he has lost. However, after a few seconds, the bug flies away.
- By the last verse of "Accidentally in Love" as used in the beginning of Shrek 2. Overlapping with the Fairy in a Bottle trope, the ogre newlyweds use several as mood lighting for their mud bath.
- Smallfoot: The yetis use glowing snails as illumination, activating them by clapping. They also believe the sun is a giant snail crawling across the sky.
- In Treasure of Swamp Castle, Caffrinka, Szaffi's foster mother who's believed to be a witch, summons some fireflies to light up her hut when it's getting dark.
- In Pitch Black, when the last few castaways are hiding in a rock cleft, they find several glowworm-like animals clinging to the rock. Gathered in a bottle, these provide enough illumination to ward off the bioraptors. Despite the bioraptors being able to operate without issue with much greater ambient light earlier in the film.
- Green-Sky Trilogy: The Kindar use lamps that are baited with honey to attract bio-luminescent moths who feed on the honey. Honey lamps also act as a game mechanic; they have a very limited use time, meaning your character could be left in the dark if they don't have a backup light source.
- In James and the Giant Peach, the Glow-worm provides light inside the peach and later goes on to light up the Statue of Liberty's torch, saving the government a whole lot of money that used to be spent on the torch's electrical lighting. It all works because the Glow-worm, like the rest of the bugs in the peach, has grown to an enormous size and is sapient.
- In Mermaid (2011) has an underwater version. The Sea Queen lights her palace with bioluminescent fish.
- Queen Medusa from the Mermaids of Eriana Kwai trilogy lights areas of her castle with bioluminescent jellyfish.
- In Mermaid's Song, the merfolk use caged bioluminescent fish to light their homes.
- The Sharing Knife by Lois McMaster Bujold features a romance between Dag (a "Lakewalker") and Fawn (a "Farmer"). At one point Fawn and Dag are on the road and are camping for the night when Dag uses his "groundsense" powers to coax several hundred—or perhaps even several thousand—fireflies into a tree (and then briefly also into Fawn's hair). The light from the insects soon illuminates a love-making session.
- In The Sorcerer's Daughter, Rothbart catches a handful of bugs to be able to read a letter in the darkness. The light they provide is very dim, but he manages to discern the writing.
- In The Vazula Chronicles, the Center of Culture is mostly lit by lanterns of bioluminescent plankton, but some street corners are lit by caged jellyfish instead.
- In Wet Magic, the Merpeople use phosphorescent fish as torches.
- Ultraman Ace: One episode have Ace dealing with a firefly monster, Hotarunga ("Hotaru" literally meaning firefly in Japanese) whose powers include a tail-light capable of discharging electricity, which knocks out and nearly defeats Ace in the peak of battle. The light in its tail can also fire a Tractor Beam allowing it to imprison humans.
- Dungeons & Dragons, Basic D&D adventure B1 In Search of the Unknown: In the dungeon known as the Caverns of Quasqueton, the library has cages in its walls that contain fire beetles. The beetles' bodies give off a glowing light that can be used for illumination.
- Pathfinder: Flash beetles are three-foot-long insects with a pair of glowing organs on their abdomens, which continue to glow for a few days even after the insect's death. They're often used as light sources by miners, as they're safer to carry than an open flame that might ignite a pocket of flammable gases and cheaper than lamps, and they're raised by many subterranean races which keep them in cages to serve as light sources.
- Level 25 of Crash Bandicoot 3: Warped, titled Bug Light, have Crash navigating his way through a dark pyramid, with his only light source being a lone firefly that Crash have to keep running ahead to catch up. Lose the firefly and you can't see a damn thing ahead of you in the level, which would likely lead to Crash running into a death trap or a killer mummy.
- Dark Tales: In Dark Tales: The Gold Bug, near the end of the game, you capture some lightning bugs and put them inside a glass lantern to create a light source.
- In Fallout 4, a Glowing One — a ghoul so heavily irradiated that it glows green — is used for a lighthouse's beacon. Each Companion has their own opinion on it: Codsworth, Preston, Nick and Cait are all impressed by the idea, while Danse, MacCready, Deacon and Hancock are dismissive of it, and Piper and Curie are more interested in the lighthouse itself.
Danse: The only thing those Glowing Ones are useful for is decorating the pavement when I gun them down.
MacCready: I don't see the point. It's not like any ships are still sailing out there.
Hancock: Putting a giant beacon in the middle of your settlement ain't the best way to keep a low profile.
Deacon: Were lighthouses just as spooky in your time? This place gives me the creeps.
- Grounded: Firefly Goo can be looted from dead fireflies and used to create hanging lamps and headlamp helmets.
- Hollow Knight: Lampposts can be found throughout Hallownest that are topped with glass spheres holding small, glowing insects (this despite all characters in the game being much larger anthropomorphic insects). If the glass is broken, the insects flutter away. The Big Bad, Radiance, is a much darker example, being the evil goddess of light whose influence spawned the Infection. As shown when you use the Dream Nail, bugs under the Infection's thrall are Mind Raped to insanity, only barely able to muster up enough sentience to ramble about the Radiance's light.
- Kukoos: Lost Pets: a firefly-like critter called Lightbulb, can "shed some light" on the situation. He can help light the way or blind any enemies that might wanna charge into you.
- Lords Of Time: Level 9 has the Tooth Fairy give you a firefly as a light source.
- Metroid: Parts of Lower Brinstar in Super Metroid and Chozo Ruins in Metroid Prime have large insect aliens that light up the rooms. If you kill them, the rooms will end up too dark to navigate safely.
- In Oddworld: Stranger's Wrath, Zappflies are the most basic ammo-type for Stranger and serve as a way to activate electrical equipment as well as to knock enemies out for capture.
- Ori and the Will of the Wisps: You initially need to release giant fireflies to light your way through Mouldwood Depths and stay close to them since the darkness will kill you instantly if you stay in it for too long. Eventually, you'll gain the Flash ability, which eliminates the need for the fireflies.
- Terraria allows you to bottle some of the forests' fireflies and the Hallow biome's lightning bugs to hang from a chain.
- Uru: Ages Beyond Myst: One puzzle involves using some fireflies to light your way through a dark place.
- Avatar: The Last Airbender: An inventor in one episode uses jars of lightning bugs as illumination in a natural gas fissure. His lack of eyebrows attests to why.
- Dawn of the Croods, taking place before the invention of fire has the characters using hybrids of deer and fireflies as flashlights.
- The Little Rascals: In "Rascals' Revenge", Buckwheat's flashlight is essentially a jar full of fireflies attached to a stick.
- My Little Pony:
- My Little Pony (G3): In the G 3.5 film Twinkle Wish Adventure, in the "Dreams Do Come True" song, a group of fireflies appear while the ponies are sitting around together at night, all glowing. One of them lands on Cheerilee's hoof and narrows its light to shine on the book that she's reading.
- My Little Pony: Friendship Is Magic: Lanterns filled with fireflies appear sporadically as light sources, alternating with electric lamps and glowing crystals. In "Read It and Weep", Rainbow Dash puts out once such lantern by blowing its hinged door open, allowing the fireflies to fly out in a way visually reminiscent of blowing out a flame. In addition to a basic portable version most often seen, variants include overhead hospital lights in otherwise fairly high-tech scenes, streetlights on top of lampposts and projectors meant to shine out directed spotlights, all based around glass jars or cases filled with glowing insects.
- During World War II, Japanese soldiers used the dried-out remains of bioluminescent crustaceans as a source of light. The crustaceans' bodies retained the chemicals that allowed them to glow when they were alive, and if water was poured over them they would give off a faint blue light.
- Bioluminescent click beetles of the genus Pyrophorus were widely used as a source of light by natives of Amazon rainforest. This was usually done by tying the live insects to their fingers and toes to serve as living lights. German explorer Freidrich von Humboldt, after whom the Humboldt current is named, wrote that he was able to read at night by the light of a dozen of these beetles.