In video games, there is a common tendency to make grenades inexplicably glow. The sole purpose of this is to alert the player, since grenades usually do a lot of damage or instantly kill. This is an acceptable break form reality, since it is usually made to not seem out-of-place. This is sometimes seemingly-justified by being in a sci-fi setting, but it still doesn't make sense from a tactical standpoint. In real life, a glowing light on a grenade would defeat the purpose of it as a lethal weapon. Feel free to add examples.
Hello, Unknown Troper. You'll need to get known to lend a hand here.