How to stop zombies from spawning in my torch-lit mines?

My mines are filled with torches, properly lit, but zombies keep spawning there. I left the ladder exposed and they ambushed me from behind killing my dude. How do I stop it from happening?

Solution 1:

Several things could cause this. There could be a slightly-too-dark corner in your tunnels or an overlooked side passage. If the light level drops to 7 or lower in any square, you need more torches.

In order to ensure >7 light in all areas, you need torches every 12 meters (blocks) in all directions. However, note that if your tunnel is more than 1 block wide, simply placing a torch on the wall every 12 blocks will result in a square that has less than 8 light at the midpoint on the opposite side of the hall. My recommendation is to be excessive in your lighting and place a lot of torches.

Solution 2:

This was actually a bug in v0.3.3 and below, as described in the MCPE forum. It has been fixed in the 0.4.0 release.

From the 0.4.0 release notes:

Bug fixes:

• Monsters could spawn indoors

To test I have ventured back into my open-plan underground mine (something like 40x40 wide and full of torches ever 4 blocks or so) which always used to spawn mobs at one end whenever I was at the other and have not seen any mobs in there since the upgrade.