Why are there mobs on my balcony?

I have a sweet ravine balcony, that I've lit up, and partially fenced off. It's not connected to anywhere that mobs could spawn yet, come night zombies are at my door creepers are lounging around and spiders are crawling around! I didn't invite them!

Is there any reason for these mobs to spawn here when it's well lit?

3 Answers

Mobs cannot spawn in a well lit area, but only a single square is enough to allow spawning. The light level must be 8 or higher to prevent spawning, meaning no cube can be more than 7 steps from a torch. You have to count vertical steps too, so a torch two squares off the floor can only be five horizontal steps from any floor square.

In addition, spiders can climb up walls, and thus are harder to keep out than other mobs. But the fact that you have creepers and zombies as well indicates that you have a lighting issue. Creeps can also fall down from heights farther than they would choose to walk; if the cliff above your balcony can spawn mobs, you may wish to light it or fence it to prevent mobs from pushing each other off the edge and falling to your balcony.

After you posted the screenshots, I made this graphic, illustrating some of the squares that have insufficient light. The green dot means that area is light level 8 or higher (within 7 cubes of a torch). A red dot indicates it is light level 7 or lower, and mobs can spawn there. As you can see, there is a large splotch of darkness on the right side of your balcony, where it is widest. Add a few more torches and everything should be fine. I did miscount a bit when creating the graphic: the leftmost two red dots should be green, as they are 7 cubes from the torch that is just out of sight on the bottom left. This leaves 5 squares visible in the image that are below light level 8.

If there is a tunnel connecting to the balcony that has some dark areas the mobs you encounter could be spawning there and be walking onto your balcony. If not then creepers could be climbing up the ladders and spiders can climb up walls as you probably know. Or the mobs culd be dropping off an above area to your balcony.

Hi I have heard you have a zombie promlem? Well I also had some problems with this. The thing is is that you might of hit a zombie spawning point in minecraft. Destroy the ladders because creepers can climb them because in 1.7.3 I had a panic room upstairs. I didn't know how to use stairs so I used a ladder. I was shocked to discover when I climbed up the ladder a creeper followed! Also spiders can climb so put either neatherrack and light it with flint and steel (because neatherrack is a never ending burning object) on the top so spiders get burnt when they get to the top, or put a block a block apart so spiders can't climb up and because your balcony is so high the spider will probably fall to their death after a couple of attempts (unfortunately I can't post an image). About the zombie spawning point there is nothing you can really do there. Hope I helped!!!!