Monsters Spawning in High Light Levels

I have created a cave (5 blocks high) to mine in, and no matter how many torches I add monsters continue to spawn. I dug up higher to see if there was a monster spawner, and found nothing. I have attached a picture of the specifications of the cave (level, height, light sources, etc.), although the monsters spawn everywhere. I have tried clearing the cache and restarting my computer.