I just built this mob spawner, one of my first, and while I was headed back up to check on it the light glitched out and went from completely dark to completely lit. I've attached a video and some stills to demonstrate the problem.

closed room lit up When I first entered the room and sealed myself in.

closed room lit by setting sun A minute later, when the sun had begun to set.

This is a free standing, above ground structure. I made sure that even the entrance I used to get in was completely closed.

As you can see, the light from the sun is shining through the stone, despite completely closing myself off. It even responds to the sun's setting.

I've had something like this happen before. A small area of grass that was completely lit up at night without any light source having been there.

I've tried a range of things: putting up and taking down torches, adding more blocks, breaking parts of the ceiling and closing it up again. Nothing does anything. Does anyone know what glitch is causing this or what can be done to fix it? or am I going to have to tear it down and build a new one?

A couple of notes: I am playing version 1.7.9, vanilla edition, single player, on a mac OSX.

  • 3
    What is the roof made out of? Commented Jun 23, 2014 at 3:22
  • How thick is the wall, roof and floor? I am not sure, but I've myself noticed that sometimes, if I build in the sky, different materials grant different levels of light shining trough, while if I build underground, it will go completely dark if I seal it completely up.
    – Sharain
    Commented Jun 23, 2014 at 8:18
  • 5
    Is your ceiling made out of half blocks or slabs? If so, that can make light shine through.
    – user79446
    Commented Jun 23, 2014 at 13:45
  • can you confirm that it does this when you turn up the graphics settings, i can see you have them lowered as the lighting levels to "blend" into each other
    – Memor-X
    Commented Jun 24, 2014 at 0:57
  • Ah yes, to clarify on a couple of those comments/questions, the entire structure is made of stone bricks and is only one layer thick in most places. I did see some videos showing the stair/slab light glitch, but that is not the case here. Additionally, the issue remains the same regardless of graphics settings and if I hit F3 it shows the sl and rl to be equivalent to whatever is outside at that time of day.
    – SemiSigh
    Commented Jun 24, 2014 at 9:09

3 Answers 3


Sounds to me like a shading issue where Minecraft is just trying to make stuff visible, but the lighting is probably still nil.

If you press F3, you should get some text in the corner of your screen. Find which one is for the light and see if it is the same regardless of your visibility. If it is, then this is simply Minecraft glitching on the shaders and you should be fine.

  • Hitting F3 indicates that the sl and rl are equivalent to whatever is outside at that time of day.
    – SemiSigh
    Commented Jun 24, 2014 at 9:11
  • 2
    You need to look at the BL level specifically. That is the (B)lock (L)ight level.
    – NocFenix
    Commented Jun 25, 2014 at 1:12

I don't have a reference to more info handy, but I've seen this myself, and this is what I recall about it:

This is a bug which causes sky light to occur where it shouldn't. It is particularly hard to get rid of because part of the glitch is that sky light occurs inside of solid blocks (where it should normally be zero) and spread out from them, which causes even properly-functioning light updates to not correct the problem as they do for the more usual all-black lighting glitches.

It may be sufficient to replace all of the ceiling, and possibly wall, blocks in the area to cause them to properly recorded as blocking light, but I'm not sure — I never quite fixed it in the affected world I had.


I have the same issue as you. I tried adding a massive ceiling above my spawner and extra walls around it and it fixed the problem.

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