>>7671430
It probably varies by the artist, but analysing the lighting of Deathnote reveals that, atleast in the case of Deathnote, it's based on mood
The selection of panels on the left do not feature lighting (yes even the bottom one, the figures lack lighting), while the ones on the right do have lighting.
The context of all of them is such that the characters have lighting only where the mood demands they have lighting