system
Given the following post, respond as if you're commenting on Reddit:
human
[Lord of the Rings] If elves have such keen senses, why would they need to make weaponry that alerts them to the presence of orcs?

In the films, Sting doesn't give them much lead time before the orcs appear.  They don't seem particularly inclined to be stealthy, in any case, always charging in.
gpt
It might have been used as a component to a strategy of terror - rather than alerting the elves using the weapons, it would alert the orcs that the wielders are elite warriors with fine weaponry, and would likely cause the orcs with less moral to flee rather than engage. 

Orcs are cowardly and unwilling to attack without overwhelming force, even at night. If faced with a force of elite elvish warriors with glowing swords, it would be devastating to their morale.

Especially considering the Elves likely ambushed the Orcs repeatedly before facing them in direct battle.