Muzzle Flashlight

Sometimes, games feature incredibly dark areas for you to traverse. Sometimes, the developers haven't given you an adequate flashlight, or perhaps you had one, but the batteries died a long time ago. How do you find your way now? Start blindly firing your weapons, of course! Your muzzle flash, glowing magic, or energy weapons are all you need to light the way, and can do so fairly well. Never mind that it could give away your position, since your enemies can probably all see in the dark anyway.

Expect little relation between a gun's actual muzzle flash and the muzzle flash it has in fiction. One of the most prominent is the AR15/M16/M4 series, which has a very effective flash suppressor as standard issue, yet tends to have a massive flash in fiction. The A2 Birdcage is so effective that armorers for live action works will often replace it with less effective ones because the larger muzzle flash looks cool.

Not to be confused with flashlights mounted to weapons.

Examples of Muzzle Flashlight include:

Video game examples

Action Adventure

Older versions of Iji required this in the deep sector. The newest version made it less dark and thus unnecessary and firing the shotgun doesn't do anything to the light level anymore.
In Famous pulls this one too: When you first pop into sewers, you generally have to go across a complicated platforming section in extreme low-light conditions... It's a good thing the main character glows in the dark whenever he uses his powers! ...Though it gets significantly harder if you're evil, since the red color just makes things harder to see.
In The Legend of Zelda: A Link to the Past, you can use your Ether medallion to temporarily show you where hidden paths are - you're SUPPOSED to light torches, but Ether is sometimes easier or more convenient, since you can use it anywhere.
Pistols in Tomb Raider can be fired in rapid succession when few or no flares remain. This is especially useful because most games in the series give pistols infinite ammo.

Action Game

Part of a level in Alien Soldier. Includes a boss fight and a rapid climbing section. Each gun illuminates the segment differently, which looks pretty neat.
Particularly easy to do in Devil May Cry, as the game grants you infinite ammo as a core gameplay mechanic.

First-Person Shooter

The ~~lightsaber~~ Dragon Tooth Sword in Deus Ex could be used as poor-man's flash light when your bio-energy was low.
In Doom, muzzle flash will (slightly) illuminate the entire visible area for a split second, letting the chaingun act almost like a short-length flashlight. This is invoked in the Doom Comic when Doomguy encounters a dark room.
In Marathon, this is pretty much the only way to see in dark rooms other than the extremely rare night-vision power-ups.
In Left 4 Dead, most weapons generate more light when fired then your actual flashlight. SMGs and assault rifles in particular are most useful for this, being full-auto.
In Quake II, the player starts with the Blaster. This gun is very weak, but it doesn't use ammo and its projectiles are slow-moving and glow brightly. This combination makes it useful for lighting up dark corridors, since there is no flashlight in this game. The sequel, Quake IV, does away with that and just gives you a flashlight.
Some Star Wars games. Energy weapons AND lightsabers. What darkness?
- The darkness in Jedi Outcast, is what. Manage those night-vision batteries well, 'cos you're gonna need 'em.
- The use of a lightsabre as an improvised lantern turned up in the Expanded Universe on at least one occasion and, of course, in The Empire Strikes Back.
In Unreal, just about every projectile weapon has some sort of glow around its shots. The biorifle's sticky projectiles can act as short-term flares if necessary.
This could be done in the Metroid Prime trilogy, although it's not awfully necessary, especially after getting certain visors. Charging your weapon also provides light.
Bit of a twist on it in Halo with the Plasma Pistol - the torch had a habit of running flat, so charging up the plasma pistol to get the muzzle glow could solve the problem. In Halo: Reach, the Energy Sword emits a blue light that can act as a flashlight as long as the sword has power.
Only three weapons in Killing Floor have an attached flashlight, and most of the default maps are rather dark, so this trope is common. Taken to the extreme with the flamethrower, which can decently illuminate parts of the map (or specimens) by setting them on fire.
In Half-Life: Opposing Force the M249 Squad Automatic Weapon provides a shitload of illumination, especially in the Voltigore tunnels...

Hack and Slash

The official guide for Diablo II suggests using fire arrows or spells to scout ahead in dark areas.

Platform Game

This is utilized in one of Eggman's stages in Sonic Adventure 2.
In Banjo-Tooie, you can use Fire Eggs to light up a dark maze over a Bottomless Pit instead of splitting up the characters so one keeps the light on, which you're supposed to do.
Spelunky has annoying dark stages where you have to carry a box of flares to see. Or if you have a shotgun or a pistol you can just keep firing it to light the place up.

Real Time Strategy

X-COM UFO Defense has incendiary rounds for some weapons that spray fire over a wide radius and provide much better illumination than the hand-thrown "electro-flares" that are intended for the job. Thanks to the hitscan mechanics, this ended up being their primary use.

Role-Playing Game

In The Elder Scrolls Oblivion you could turn practically any weapon into this; magical weapons glowed, plus any spell or enchanted armour could include the "light" effect which made the target give off light.
Dark Messiah has a "see in the dark" spell, but for those who don't like seeing in blue all the time, most spells and a few magical swords can be used as lights too. Lightning bolt is especially good at this.

Shoot'Em Up

In Jungle Strike's night level, pretty much the only lighting comes from weapon fire.
Star Fox 64 has an underwater level that had little light, and your bombs are replaced by an unlimited supply of glowing torpedoes.

Stealth Based Game

At one point, Metal Gear Solid 3: Snake Eater dumps the player in the middle of a pitch-black cave. Though more traditional light sources are available, New Game+ provides you with an infinite-ammo machine gun...

Survival Horror

The Toy Sword in Dead Rising emits a red-pink glow at night, which is supposedly extremely useful for SDTV players because the game was designed to play on an HDTV and it becomes very difficult to see anything at night on an SDTV.
Seeing all four endings in Afraid of Monsters: Director's Cut unlocks a machine gun with infinite ammo. Consider how dark the game normally is, and one can imagine its primary use.

Non-video game examples

Anime and Manga

In ~Yu-Gi-Oh!~, the first time Yugi sees Panik's monsters is when his dragon fireballs them.

Comedy

The Dead Alewives comedy group has a famous sketch featuring Dungeons & Dragons players. One of them casts Magic Missile at the darkness ahead of him, which reveals an elf.

Film

Brief strobelight-esque illumination occurs when Clarice kills Buffalo Bill at the end of Silence of the Lambs.
One scene in Equilibrium is lit entirely by muzzle flashes. (Although the characters don't really need to see in order to fight.)
Variation in Saw. One photographer has to use his camera flash to try and see if there's an intruder in his house when the power gets cut. There is.

Live-Action TV

An episode of Doctor Who brought back the Weeping Angels, which can only move when no-one's watching, and turn into indestructible statues when they are. A squad of soldiers attempting to hold them off in a dark corridor were reduced to trying this as a last resort - that, or they were going for the good old Who tradition of Five Rounds Rapid.

Tabletop Games

A few flaming weapons in GURPS: Dungeon Fantasy have the effect of a torch when active.
- And in Tactical Shooting firing guns in the dark can cause temporary blindness.

Web Comics

In Goblins, Dellyn Goblinslayer uses the Magic Fang spell in this way - he's trapped in a lightless sewer, and the spell makes the sword glow.

Western Animation

In the first Season Finale of X-Men, Wolverine battles a squad of Sentinels in a dark cave, with nothing to see with except the flashes from the Sentinels' laser blasts.

Real Life

On the night of October 6, 1973, during the battle of Booster Ridge, the Israelis were at a disadvantage because their Centurion tanks were not equipped with night-vision cameras comparable to the ones on the Syrian T-55s, so Lt. Col. Avigdor Kahalani used a burst of tracer rounds from his machine gun, fired into the air, to illuminate what he thought, correctly, might be an approaching T-55. Once his suspicion was confirmed, he knocked out the tank with his main gun, and the resulting fire illuminated the battlefield.
Another point of Truth in Television: The muzzle flash of a good number of weapons is just plain ludicrous. A Mosin-Nagant's flash can set people on fire. The Mini-14 sans flash suppressor can produce a flash as long as the rifle itself.
- Some ammunition makers try to avert this by offering rounds with powder that is specifically designed to minimize flash, typically aimed for home defense purposes.