I came upon a lighting bug where a large rectangular portion of the surface had block light = 0, despite the in-game time being about midday and the tallest structure nearby being a two story villager plains house. It is more than a visual glitch as can happen occasionally, as hostile mobs had spawned in great numbers and undead mobs were not taking fire damage.

I am unsure as to how this can be recreated, as I simply happened upon it- though I can say that it occurred outside of the spawn chunks area.

I have uploaded a screenshot of the issue below