This trophy requires you to eliminate the three main targets in the Sniper Assassin game mode (Dorian Lang, Guillaume Maison, Doris Lee) with the level's cannon, which is located on the top floor of the mansion.
So, after you load into the level, you're going to shoot down the chandelier located in the top of the mansion's tower. The reason for this is because the three targets will meet up at this location towards the end of the timer (roughly when there's 4-5 mins left).
However, with the chandelier now blocking access, they will instead meet up in the room circled below (again when there's roughly 4-5 mins left on the clock).
Side note: On a separate run through of the level, eliminating the three targets with the chandelier will complete the Heavy Burden challenge.Once the targets are all at their new meeting point, go ahead and aim slightly to the left of them and you'll see the cannon laying in wait behind the window. Fire away at the back of it and enjoy the result.
Eliminating them with this method will complete the
Got A Light? challenge, as well as grant you the trophy.