In a nutshell, this is using sunlight as though it was a stage spotlight.
Spotlights in theater are often used to highlight a specific thing the play wants the audience to focus on. Thus the other lights are turned off so only what's in the spotlight can be seen.
In media that isn't on stage, even animated media, that isn't an option outside of stylistic works. Other ways have to be found to highlight things. This trope is when light streaming through things, like through windows or tree branches, is used to highlight something relevant. Heck, sometimes there doesn't even have to be something making the sunlight act like that. It just makes the slits on its own.
Usually it's something key to the plot, often of a supernatural nature. The latter sort of justifies this trope, but it's not the only form this trope takes.
Quite common in some Western religious artwork.
Note this can only be when it's used as a substitute for a spotlight. If sunlight is actually used in the story to highlight something, like killing Dracula or finding the location of the Ark of the Covenant, it's not this trope.
- The opening of Fullmetal Alchemist (2003) has this at the end coming through the roof of a building with Ed holding his hands up to the light.
- In D.Gray-Man, "Old Man of the Soil and a Lonely Night's Aria", a spotlight of moonlight shines down on Guzol and Lala in their underground hideout at the moment that the Exorcists find them.
- In the Fate/stay night Anime, Archer appears to summon a natural spotlight (probably the Moon, although it's odd considering the angle changes) before he uses Unlimited Blade Works.
- Dungeon Keeper Ami: In "Crystal Investigation":
The gem was lying on the broken tip of a chalk-white stalagmite. It glittered in the single ray of sunlight that shone like a spotlight through a tiny gap in the cave’s roof.
Ami didn’t believe for an instant that the crystal had landed in the only illuminated spot by sheer good fortune. This was either an attempt to mislead her, outright mockery, or possibly both.
- Done in exactly the same way in Disney's adaptation of The Sword in the Stone.
- Another lit face is Anya's, in the Anastasia movie. The eyes are the ones in focus, which makes one wonder whether or not she notices; most people would certainly be blinded by such thing.
- Snow White's glass coffin at the end of Snow White and the Seven Dwarfs.
- Sleeping Beauty: Aurora asleep in the tower.
- During the song "Hellfire" in The Hunchback of Notre Dame, this happens with moonlight through windows a couple of times.
- Cinderella: When Cinderella is brought into her stepmother's bedroom to be admonished, sunlight shines down on her from the large window. For added effect, the shadows of its muntins also appear on the light, making it look like she's in a prison cell.
- Lampshaded in The Blues Brothers. "Do you see the light?" It's even justified here: the Sun is breaking through some clouds and then coming in through a small window; Joliet Jake is (by coincidence? divine intervention?) located in just the right spot for it to fall on him.
- Godmothered: The sun shines selectively on Mackenzie's letter, which allows Eleanor to find it.
- A few scenes in The Lord of the Rings: The Fellowship of the Ring, like Balin's tomb. Balin's tomb was described like this even in the original novel, explained by ingenious light channels carved by the dwarves in the mountainside. On the other hand, the one lighting Gollum's cave in the prologue comes off as highly improbable, considering its depth and the fact that Gollum can't stand daylight.
- In The Addams Family movies, Morticia's face always has a light on it. It is rather obvious and jarring.
- In Serenity, Mal's speech to his crew before the final action sequence is lit with copious amounts of light directed at him by overhead windows. In the commentary, Joss notes that on the one hand, this is vaguely believable, but still exists solely because it was awesome.
- In The Hunger Games: Catching Fire during night suddenly a small strong circular spotlight illuminates Katniss after she proved willing to sacrifice her life to destroy the tool of the evil empire.
- In Frailty, when Dad is guided into an abandoned barn to receive God's demon-hunting weapons, it takes the form of an axe and a pair of gloves on a tree stump, illuminated by a hole in the ceiling. The situation is vague enough that it could be God highlighting them in a holy fashion... or it could just be a natural occurence that Dad's unhinged mind is pinning religious undertones onto to justify becoming a murderer.
- In the most recent book of The Wheel of Time series, main character Rand gets one of these shining on him during a key character moment. Possibly justified by the fact that his ta'veren nature warps probability (Its Complicated) and the combination of his being a Fisher King and slowly growing more and more insane has resulted in a continent-wide pattern of overcast weather that only starts to break when he begins to get his screwed-up little head back together.
- Dirk Gently's Holistic Detective Agency:
With an impeccable timing of which it is very rarely capable, the sun choose this moment to burst briefly through the gathering rainclouds, and as she played her cello a stormy light played on her and on the deep old brown of the wood of the instrument. Richard stood transfixed.
- The Master Sword in The Legend of Zelda series is often shown this way.
- In Metroid Prime there are a few places where Chozo Statues are resting, the ceiling is cracked and sunlight gets through. (And yet on the "Overworld", it's constantly raining.) The sunlight may not be directly on the statue, but it's close enough to give that entire room that effect.
- Metroid Prime 3: Corruption has a similar statue bathed in sunlight hidden in the depths of Skytown.
- On Ilos in Mass Effect, the VI Vigil is in a small room, where a shaft of light shines down on it.
- In Splatoon 2: Octo Expansion, one of the few working light fixtures in Deepsea Metro Central Station shines down on an antique telephone in the center of the area, as if it could possibly be pointed out any more. As one could expect, answering the telephone provides you with your objective and allows you to proceed into the subway.
- Tower of God: Rachel, after she broke through the ceiling of Bam's cave, was fully lighted from the hole she just made, standing on a pile of rubble.
- Used both straight and parodied in The Simpsons.
- This occurs in the Bugs Bunny short What's Opera, Doc?. After Elmer Fudd's character discovers that "Brunnhilda" is actually Bugs, he summons lightning bolts to "Kill the wabbit!". When Elmer goes to see what happened to Bugs, the area is dark and a shaft of sunlight shines down to reveal Bugs' lifeless body.
- Parodied and used as a Running Gag in the Kaeloo episode "Let's Play the Quest for the Wholly Gruel".
- Also in the pilot, where Stumpy sees rays of light from the sky shining onto a pair of roller skates and a chainsaw.
- This actually happened to Abraham Lincoln right after he finished his Second Inaugural Address. No sooner was the speech done when the sun burst out of the clouds and illuminated the president. Even he was shocked by it.
- It is told that Joseph Goebbels exploited this for dramatic effect during one of the Nuremberg rallies. As the clouds were shifting, he timed his speech just long enough to make sure the sun came through in time for Adolf Hitler to enter the podium. The effect was staggering.