Nuclear Candle

A single match is always enough to magically light up a room bigger than the Colosseum.

—Hollywood Rule Book, Vanity Fair (April 2002)

All the light sources are either broken, out of energy, out of fuel (includes wax) or simply not there. The scene is illuminated by a single light. This can be a flashlight or electric lantern, but is usually a lighter, a candle or a matchstick.

And yet, despite the tiny size and almost insignificant lumen output of the thing, everything looks as if the light was powered by a nuclear reaction. Rooms, even quite large ones, will be lighted to almost daylight level.

But if the matchstick is depleted, or the batteries or fuel runs out, the light extinguishes and everything is suddenly pitch black. Cue the monsters, the traps or the sentimental/sexual plot twist.

The trope is possibly semi-Justified, if we are to consider the difference even a faint light source would make to someone whose eyes have already accommodated to the darkness. Compare Hollywood Darkness, where the ostensible light source is either natural or completely inexplicable... And usually blue. Often appears in the same context as (and immediately after) By the Lights of Their Eyes—it wouldn't be much of a Reveal if a darkness-shrouded monster stayed darkness-shrouded after the candle was lit.

Contrast Chiaroscuro, where everything looks like it was actually lit by a candle.

Examples of Nuclear Candle include:

Film -- Animation

Averted in Atlantis the Lost Empire. Rourke lights a match in a dark chasm and it's only bright enough to light his face. Nothing else can be seen until everyone turns their vehicles' headlights on.

Film -- Live Action

In Die Hard, the main character is advancing in a ventilation shaft, illuminating his way with a Zippo. The light provided is, however, more akin to a searchlight than to a small flame.
Averted in Stanley Kubrick's Barry Lyndon which was the first film to use special lenses and sensitive film stock so that scenes could be lit using candlelight. They still needed a lot of candles, though. Modern film stock or digital cameras make this easier, though it's still quite rare.
In Scary Movie 2, when Cindy shows Buddy the secret study, he lights one candle, which then illuminates nearly the whole room. As this is a parody film, this is likely intentional.

Live Action TV

An episode of the Jennifer Ehle/Colin Firth Pride and Prejudice (set in 1810-ish) has the Bennetts sit down for dinner. The room is brightly lit as if by sunlight, but behind Mr Bennett you can see it's pitch black outside. There's no way candles or oil lamps could produce such perfect light.
An episode of Friends does this. There is a blackout, and the friends are bringing in candles for light. Later on, all the candles but one are extinguished, and yet the light level is almost the same. One of the characters then blows on this last candle extinguishing it, and everything goes dark. A sentimental plot twist follows.
An episode of Little House On the Prairie does this very badly. One of the girls is kidnapped and trapped in a pitch-black cellar... when her captor checks on her while holding a small candle, it's suddenly as if a spotlight was shining down.

Theatre

In Rosencrantz and Guildenstern Are Dead, the second act opens in near-darkness. Then Hamlet lights a single oil-lamp, and the stagelights all come on. The stage directions even note that this is highly unrealistic.

Video Games

The Legend of Zelda 2. If don't have a candle, you cannot see any enemies in dark rooms, even if they are inches in front of you. Once you get the candle, they're visible even if Link and the enemy are on opposite sides of the screen.
- The original The Legend of Zelda was even worse. Candles lit up dark rooms by tossing a single fireball that burned for only a few seconds.
Pokémon's Flash ability used to do this, lighting up dark caves entirely (what made some caves pitch-black and others not was never explained). In the newer games, though, it's just an expanded circle of light around the player.
Prey has Tommy's Zippo. It's not as strong as other examples in this page (it only lights up a small area ahead of you), but it still gives off much more light than a real lighter.