peaceful surface is a mod that greatly decreases the chance of hostile mobs appearing on the surface of the world. By default most Minecraft enemies spawn with a light level of 7 or less, with this mod only hostile mobs with a light level of 0 will spawn i.e. only in darkness absolute.

This change to the lighting value needed for a hostile entity to spawn in Minecraft will cause enemies to spawn only underground in Minecraft and only when there is no light at all. So now you can enjoy the calm on the surface of your Minecraft world.