[MC-102162] Some light-emitting blocks (magma, lit furnace, lit redstone ore) 'save' block light

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 /setblock to 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.

Linked issues

is duplicated by 10

MC-102180 Light from a source block stays bright after destroyed with magma blocks close by. Resolved

MC-102182 Magma Block Lighting Bug 16w20a Resolved

MC-102243 Magma block not taking the light given to them Resolved

MC-102304 Light Level glitched after using Lamp for Magma Block Resolved

MC-102417 Magma block holds light of daylight then when night looses it Resolved

5 more links

relates to 1

MC-138015 Magma Blocks not absorbing light levels Resolved

Attachments

Comments 23

Daniel Burnett 2016-05-20T04:01:48Z

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 2016-05-20T22:57:57Z

it's a feature

kumasasa 2016-05-21T08:01:59Z

@unknown:

it's a feature

Source ?

marcono1234 2016-05-21T15:44:33Z

Affects activated redstone ore as well

[Mod]Les3awe 2016-05-23T15:24:38Z

Can confirm.

13 more comments

Meri Diana 2016-06-08T16:56:10Z

Confirmed for 1.10 release (and the previous prereleases).

Hayden Muhl 2016-06-14T08:27:30Z

In 1.10, I was not able to reproduce the bug from daylight. The magma block only seems to react to block light.

Anomie X 2016-06-14T11:10:35Z

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 2016-06-15T21:03:50Z

Also affects lit furnaces.

[Mod] redstonehelper 2016-06-15T21:07:37Z

Do lit furnaces keep light levels or do lit furnaces light up the magma block?

Skylinerw 2016-06-15T21:14:06Z

My bad, I meant that lit furnaces (and lit redstone ore) behave like magma blocks and keep light levels.

marcono1234 2016-07-11T10:16:11Z

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.

M 2016-08-17T21:52:50Z

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

Daniel Burnett 2016-08-17T22:36:52Z

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.

Meri Diana 2016-08-18T09:52:00Z

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".

Wesley DeLora 2016-09-17T18:42:58Z

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.

Syl2010 2016-10-02T01:43:05Z

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 2016-10-02T13:49:19Z

@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.

kasamikona 2016-10-03T07:42:19Z

@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 2016-12-31T20:24:24Z

@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 2017-01-01T03:12:14Z

@@unknown Yes, the linked [MC-3961]: "Water, Cobweb 'save' skylight".

Fors Coyt Anderson 2017-07-30T09:43:47Z

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.

Василий Алексеевич Калинкин 2018-10-30T14:24:45Z

so, will light storing feature return?