Mark of the Ninja

There are certain spotlights that cannot be destroyed with darts. You need to target these with dusk moths, hence the name. There's an eligible spotlight at the beginning of A Change in Course.

On the very first level of the original Mark of the ninja, there will be a bit where Ora says we need him to look the other way and a guard will be at the bottom of some steps and you're meant to throw a dart at a gong or at the spotlight but instead throw dusk moths at it and you will get the achievement.