Note
This issue is about block light. For the related sunlight issue, see MC-3961.
The bug
Certain blocks "save" block light, emiting it even after the original source has been removed.
Affected blocks
Lit furnace
Lit redstone ore
Magma
Reproduction
Build a sealed room without any lights in it with a single layer between it and the sky.
Use
/setblockto create one of the effected blocks.Measure the value of block light using.
Put a glowstone block right next to the effected block.
Break the glowstone.
Observe that the lighting value (as seen in F3) has changed.
Notes
All of the affected blocks are full cubes that emit less than 14 block light. (Non-full-cube blocks such as brown mushrooms (1 light) are not affected, and the effect isn't observable for bright blocks)
The resultant light is 2 less than the light value of the block you placed next to it, which is 13 if glowstone is used. This is because the block receives (and thus emits) the light level - 1, and then another - 1 occurs due to going back to you.
This behavior randomly decays
This behavior when using magma blocks is fairly popular for builds (as it is nice for decorations). If removed, it may be beneficial to introduce a similar behavior within the block's state and use an upgrade path to store the current light.
Related issues
is duplicated by
MC-102180
Light from a source block stays bright after destroyed with magma blocks close by.
MC-102182
Magma Block Lighting Bug 16w20a
MC-102243
Magma block not taking the light given to them
MC-102304
Light Level glitched after using Lamp for Magma Block
MC-102417
Magma block holds light of daylight then when night looses it
MC-102713
Magma Blocks Retain Light
MC-103271
Light bug
MC-104678
magma light issue
MC-114181
Magma Blocks Losing Light Level
MC-137049
Magma blocks change light level when pushed/pulled
Attachments
Comments
migrated
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Can confirm. I also wanted to add that, since this occurs with sky light as well, I wonder if it might be related to this old bug: MC-3961
Just to help point the devs on a possible bug-hunting path...
Brandcraft06
it's a feature
kumasasa
@unknown:
it's a feature
Source ?
marcono1234
Affects activated redstone ore as well
[Mod]Les3awe
Can confirm.
migrated
Confirmed for 1.10 release (and the previous prereleases).
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In 1.10, I was not able to reproduce the bug from daylight. The magma block only seems to react to block light.
migrated
I could reproduce it sometimes with sky light, and sometimes not. Among other things, it seemed to depend on whether the magma block was already shining with absorbed block light.
Skylinerw
Also affects lit furnaces.
migrated
Do lit furnaces keep light levels or do lit furnaces light up the magma block?
Skylinerw
My bad, I meant that lit furnaces (and lit redstone ore) behave like magma blocks and keep light levels.
marcono1234
It appears that this happens for all full cube blocks which create light. When you lower the light level emitted by glowstone using a mod or a decompiled version of Minecraft you can see it there as well. I am unsure what causes it though.
migrated
Even if this is a bug, I don't want it to be fixed. It has been very useful for building rooms that i want to be a little darker than if they were lit by torches or glowstone
migrated
William, if you want a lower light level, just move the light source further away. Anyway, it'd be much better if an analog light source were officially added as a feature than to rely on this; with this bug, the "absorbed" light isn't saved with the world when a chunk unloads and it can't be lowered or removed without piston-pushing or breaking the block. Even if the final result is useful, it's far too buggy to keep in the game in its current state.
migrated
Agreed, this is a buggy behaviour, and in my case I'd prefer if the magma block would consistently only emit very few light (light level 3), so I can use it as very dark light source that does not change when there is another light source.
@unknown If you want darker light, take redstone torches? Ender Chests also emit the same dim light level like redstone torches.
Generally, it'd be great if we could get a designated lamp block for that, e.g. that emits light depending on the POWER LEVEL it gets fed..
e.g. redstoneblock directly touching it (or redstone torch) > light level 15; if you hook it up via redstone wire > accordingly dimmer light level, so you can have all light levels you want.
I'm assuming it could theoretically be done with the redstone lamp we already got ingame.
In any case, from my perspective (also seeing it as mapmaker) this bug needs to be fixed and not be seen as "feature".
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I have to agree with Willem; You can also make a special setup that only dims the light level by one per activation... As far as it being too buggy? Not really; Even so much that I thought it was an intentional feature... I really do like the idea of a special block that does this purposely though.
migrated
this bug not only appears on light-emitting block (obsidian is not a light-emitting block)
Windows 10 64bit
Java 8.101 64bit
Launcher MultiMC 0.4.11-751
Minecraft Snaphot 16w39c
marcono1234
@unknown that might be a different bug. I assume you cannot always reproduce what your screenshots show, whereas the bug described here can always be reproduced.
migrated
@meunier That is a different issue, and is much more closely related to standard lighting errors (like water stuck lit in random places, dark patches under cliffs, etc). I had that same issue yesterday and it was very hard to reproduce and also created some strange shapes like you'd expect from lighting errors. Therefore different bug.
TheTamedWolf
@helper Is there another report of blocks keeping lit even after the light-emitting block is destroyed? This is my problem and I am not using magma blocks whatsoever. Haven't even placed one yet or even mined one in the world I am using. I can't seem to find an existing bug on this, I just happened upon this report and figured I'd ask.
pokechu22
@@unknown Yes, the linked [MC-3961]: "Water, Cobweb 'save' skylight".
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I didn't know this was a bug. I thought it was a feature. It would be nice if the Magma block did hold the light level because it would make it useful in other builds and as lighting at night instead of only supposed to add 3 to darker blocks around it. I am actually a beta tester for Minecraft pocket Edition on which the magma block doesn't even do that. I will add a screenshot to this issue on Pocket edition to show what it actually does.
migrated
so, will light storing feature return?
Fry