I think it's possible that Lucifer's light powers may just have been super effective for dealing with the shadowy spirit. Kinda like how in pokemon you can take down higher level pokemon by using type advantage.
Also, we've seen Spender fight in the dark and he had to scrounge for every bit of light. If his powers are dependant on lightsources I imagine in daylight, on a sunny day, he'd be far more powerful than at night in a forest (where you don't even have streetlights).