How To Prevent Hostile Minecraft Mobs From Spawning [duplicate]

My minecraft fortress is continually plauged by mobs every night of all kinds, even though it has spider-blockers and is very well lit. It is in the middle of a desert and is open-roofed with a wooden floor. Mobs seem to spawn even in the most well-lit places (torches are the light source here)

My Fortress

The other Question DID NOT say how to find the light level of an area (thanks to fredley), and this question pretains to a SPECIFIC building which I thought was well lit. (response to claim for duplicate)

Solution 1:

Press F3 and you will be able to see the light level of the block you are standing on.

You can use this to check whether the light levels are dropping below 7 anywhere. Check those cobblestone 'beams', and anywhere else where mobs could spawn and then descend into the room. It does look like you've got some dark patches there though.

Solution 2:

There are multiple ways to prevent spawning, of which:

• Be more 128 blocks away as all mobs will despawn

the most commonly used are :

• Have enough light to overcap the limit (7 in overworld)
• Have non opaque blocks on the floor like slabs, glass

Be warned: being open roofed does not prevent spawning. It only reduces the chances.

For more details: look at the wiki Example picture

Solution 3:

I'm assuming that all doors and walls outside are closed so nothing can get in. In that case, are you sure that you have lit up every part of the fortress? Every tile, be it under the stairs or on the roof beams that are visible in your picture have to be lit on their top side so that nothing can spawn on them.

I would guess that the beams and generally top of the walls could be the spawning places. But a picture of the fortress at night would help nonetheless.

And if you want to switch off hostile mob spawning altogether, you can always play on peaceful difficulty.