An idea I had that might work well in a FPS. Since dark levels require a time-limited light source to navigate them, why not have- flares? They’d be a findable item, you could have so many in inventory, each would last so many seconds, you could carry it with you, drop it to light a spot, and brandish it or throw it as a weapon. Substitute “torch” for a longer lasting version, etc.
Lara Croft had them.
Or just crank up the gamma. 
Metal Gear Solid 3 had a torch which was very useful for finding your way in caves and scaring off bats.
Rainbow Six had chemlites.
Half-Life 2 has 'em. They light up a little patch around you. You can also toss them around to light zombies on fire.
Unreal had flares.
Oblivion has torches - they occupy a hand that could otherwise have a weapon or shield, and casts a short ranged, wavy light source (looks pretty cool). You can also acquire night vision through magic and alchemy, though - and possibly as a racial trait, I can’t remember.
Thief 3 most definitely has flares, and it only lets you carry a fairly small supply of them.
This is one of those things that sounds cool but ends up being tedious as all get out. But as mentioned, at least Half Life 2: Episode 1 made them useful in other ways – you could burn entire groups of zombies with a little flare. Pretty weird but I won’t complain when it’s saving my bacon in the elevator fight.
AvP has them. it’s really too limited to be useful by itself but you have a self-recharging battery torch too. the game did very well to place you into the shoes of the human-surrounded-by-aliens atmosphere. very often i find myself camping for a short bit, surrounded by flickering flares, waiting for the bloody torch to recharge its batteries.
remember: short controlled bursts.
Word. Refer to Doom 3 for more info. In that game you had a flashlight rather than torches, but you had to stow your weapon in order to hold it, a cheap contrivance to up the scare factor of the game. About a week after the game came out someone released what they called the “Duct Tape Mod,” where your character discovered the wonders of duct tape and stuck the flashlight to his gun. This moved the flashlight to another button and allowed you to turn it on/off while still using your weapon, improving the game greatly (from travesty level all the way up to kinda sucky).