It works fine when using it indoors, and even a few places outdoors... but most of the time when I use it outdoors, it produces weird yellow glitches -- random lines and flat polygons that can slow down the game or make it stutter. Not sure what's causing it...

And, making things a bit more serious, it appears that weapon muzzle-flare causes the same effect.

Known problem with no fix. It's caused by grass, you can disable it in options (called detail textures or something like that).

I suggest increasing gamma and forgetting about the lantern

Here are many uses of flashlights. It helps us to find something even in deep darkness. Sometimes we can make fun with its various light effects.