User blog comment:Shadow789/Zombie spawning/@comment-7697305-20130901001411

That is mostly true. According to the "Spawn" page, the only things that affect the spawning of mobs in Terraria are the presence of player-placed background walls (which stop spawning entirely) and the presence of NPCs (which reduce the spawning rate and limit in a certain area around their homes, except during Blood Moons). Light (from torches or otherwise) does not affect monsters' spawning at all.

(Note that monsters spawned by statues ignore all of the above, and follow their own rules regarding spawning limits.)