When the darkling starts to pull back and hide, Lights actually starts to relent. Just as long as he isn't being attacked by shadows anymore - he's actually sort of relieved that that confrontation can be over, because he wasn't expecting it to come back and bite him like that.

He doesn't make any more light, but he does shout after him.

"If by 'fuck with' you mean run away with your ass limbs tucked between your legs like a raging douchebag!"