Steps to reproduce
Build a platform out of solid blocks with glowstone every 5 blocks in an alternating pattern, as shown here:
[media][media]Set time to midnight.
Set weather to clear and wait a while.
Set weather to thunder and wait a while.
Expected result
Drowned do not spawn in the water because the glowstone lights all of the water to light levels from 9 to 13, and thunderstorms should affect only sky light levels, not block light.
Actual result
Drowned spawn on all of the solid blocks (though not on the glowstone itself) during thunderstorms.
Note
More general testing described in this comment.
Original summary
Drowneds Spawning In 1-Block Deep Waters With Light Level 8+
Original description
Recently, drowneds have begun spawning in a large pool of water that should be drowned-proof and has been working since 1.16.40. The waters are 1 block deep and I've arranged the glowstone on the floor of it using a certain method to keep the light level of the waters to be at least level 8 at all times so drowneds shouldn't be able to spawn. The glowstone in the 1 block deep waters have been arranged to keep the light levels in the waters to be at least level 8+ at all times. This does work because during the day and night, drowneds don't spawn there. In fact, I've only seen them spawn when it thunders. So I did some research. Thundering is said to lower the sky light dramatically, allowing mobs to spawn in unlit areas during the day. The problem is, the internal light levels of the waters are already enough to stop drowned spawns (since they only spawn in levels 7 and lower). The decrease of sky light from thundering shouldn't be able to affect the internal light level of the 1 block deep waters from the glowstone as I've already said, the light from the glowstone arranged in this pattern already provide enough light to the waters to prevent drowneds from spawning during the day, night, and rain. I'm assuming it definitely has something to do with thundering and the effect sky light has on mob spawning.
Linked issues
relates to 2
Attachments
Comments 16
This is on an 1:4000 Earth map from motfe.com, converted over to Bedrock without any modifications, so I'm not sure what the biome is in the water. However, that water had already existed in the map to begin with, so I'm assuming it's possibly an ocean or river biome as I can't find any information on the water biomes on the website I got the map from.
Nevermind, I find the info. The water is in an ocean/deep ocean biome, but there were islands that existed there previously that I had removed (some blocks may be land biomes within the water body).
I built a layout like the ones shown in the picture in a cold ocean biome, and I am not getting any drowned spawns. My guess is that there is a single water block that is not close enough to a glowstone or other light source. You can test this by making a copy of the world, switching to creative, and using command blocks to mark where drowned are spawning.
First command block: repeat, unconditional, always active
/execute @e[type = drowned] ~~~ setblock ~ ~-1 ~ emerald_block
Second command block (attached to side of first command block where first is pointing): chain, conditional, always active
/kill @e[type = drowned]
Let those run a little while and you'll be able to see where the spawns are occurring by where the emerald blocks are.
I have completed my testing. The issue has been resolved. Thunder no longer seems to disrupt block lightning, and drowneds are now also incapable of spawning in 1-block waters. You may resolve this post.
I have retested each combination listed in the table in my previous comment in 1.16.221 Hotfix and got the same results. Also, drowned do still spawn in 1-block high water.
Here is a simpler test word and a demo video using that world in 1.17.2. Use the test world as shown in the video. During thunderstorm weather drowned spawn in water that should be at light level 9 and 11 due to the glowstone.
[media][media]
This is fixed as of the current release. Was probably fixed earlier, perhaps 1.19.10 with MCPE-155808.
Okay, it's still happening whenever it thunders (during both day and night). I don't understand how drowneds are still able to spawn when the skylight decreases (during thunder), but the block light levels of the water are all above 8 which is high enough to prevent them from spawning.