Sighvatur's Troops Arrives, Fight!

Time went by slowly, each passing second increased the nerves of the warrior.

"THEY ARE HERE!!!" A man screamed and the lights that lit up their camp shut off, concealing them in complete darkness.

Finn was responsible for this because he was aware of what would happen if they saw them with those numbers, they would be sitting ducks, he waited for arrows to descend from above because that was a strategy commonly known.

"What is going on?" Finn thought to himself, he did not see anyone advancing or arrows coming down.

"They are not attacking?" Another Viking said and Finn was surprised by this because they were informed that the enemy was coming but no one came. 

"Fuck! We have been made!" Another man screamed, and he was right, the turning off of the light only informed them of their presence. 

Why did they choose the cover of darkness to attack?