All solid blocks can pass light when converting a world from 18w16a to 18w20 +

This issue affects 18w20c as well, and only in old chunks. Caves in newly generated chunks are fine. I added a spectator mode screenshot of chunks generated in 18w16a. What's really weird about this issue is that it's seemingly random. Some parts if the caves have 0 light (as they should) while with others pulling up the debug screen will show the light level as 15 sky, 0 block. If you go to one of the dark spots (0 sky, 0 block), they will light normally and update once light sources are destroyed. The light spots change with the time of day, and will always be 15 sky, 0 block, regardless of the distance from the surface. Interestingly, the light level of the light spots can be decreased slightly by placing new solid blocks overhead (the sky light level will update to between 11 & 13)- this only occurs for one layer of overhead blocks, the light level does not decrease again for subsequent layers. 

I believe this issue is also related to weird lighting on the sea floor: MC-128299. I've attached a screenshot of an unlit area of the ocean floor- as you can see, some areas appear to be lit while others do not. The "lit" areas show the sky light level to be 15, and the dark areas show the light level to be 0, just like in the caves. (Ignore the air pockets on the ocean floor, this is an unrelated issue: MC-129625) Like with the caves, newly generated ocean does not have this issue.

To add to Rat Dog's comment above- If you go and stand in one of those dark cave, log out, and then log back in- the cave within chunk you are in will now be lit up.

Affects 1.13-Pre1 too. Really hope this is fixed for 1.13's main release!

Please fix. My game is messed up because of this. :/

If this works from 1.12.2 -> 1.13-pre3 we are going to have to consider this bug fixed.

It's better but not perfect from 1.12.2 -> 1.13-pre3 but I found this in my world where I updated from 1.12.2 to 1.13 Pre3

I just tried a copy of my 18w16a world in 1.13 pre 3, and I have not noticed this issue anywhere in my map thus far.  I was having this issue in 1.13 pre1 in almost every block when I tried that release so maybe it's fixed?  That or there is something special with my world.

Can also confirm my 18w16a world is now spawning plenty of mobs after converting to 1.13 pre 3 but hardly any in 1.13 pre 2.

@unknown, that would be MC-128299.

I fixed the light bugs in my world.
Its not to difficult, just place a solid block at the highest point of your building.

Or fill a big area above your building and re-join the world, in my cases, it worked pretty well. 🙂 (aka. the lighting was correct after it)

I think it's back in 1.13-pre7, Welsknight seems to have had this issue in his survival series Kingdoms. https://www.youtube.com/watch?v=kVTeI98RY4g&t=758s
you can easily see it if you skip to 12:10

There are two issues which report this bug (except converting a world from 18w16a to 18w20) in 1.13-pre8: MC-133598 & MC-133553.

This issue has persisted into 1.13's full release for me. Danny Kessler's solution didn't work for me

latest snapshot still has this issue. My mob spawners won't work.

It is so strange that some people are still experiencing this issue, Hmm..  My 18w16a world works perfectly after being updated to 1.13.  Don't know what would cause a difference with some worlds vs others, perhaps world type or generator options maybe?

Can anyone confirm for 1.13.1-pre1?

Still happening on ps4

Java Minecraft isn't available on Playstation 4. Please make another report, if you're experiencing issues for Legacy Console Edition.

I was still experiencing this issue in 1.13.1, but it is definitely fixed in 18w43a.