I am trying to make a landmark for my map, and the landmark has flashing lights at night. However, some of the light "bleeds through", making two of the sides always lit up. The flashing lights use redstone torches BTW!
This is what it looks like:
And this is what it looks like from the ground level:
Any ideas on how I can stop the light from "bleeding through" the sandstone?
This sounds like the following bug, which has been in the game for a very long time (the report is marked as resolved but awaiting confirmation that it still occurs in the latest version so it would be useful if you could post this example there, provided that it is in vanilla as bugs in modded versions, even the most minor mods, are invalid):
Also, I know at least one, if not the only cause - the game doesn't update light levels unless chunks are loaded all around the chunk the block being updated is in (i.e. at least a 3x3 chunk area); I was able to eliminate ghost lighting left behind by fires by not ticking them unless the chunks around them are loaded (an indirect consequence of fixing this bug), and greatly reduced other occurrences by updating the light level of the block itself if a full light update isn't possible (this mainly manifested as ghost lighting left behind by water flowing over lava, where the obsidian itself actually emitted light since it wasn't updated, and it was very hard to fix without mining the obsidian itself, unlike lighting glitches in air/transparent blocks. I still sometimes see this happen due to fluid updates during world generation happening up to 8 blocks away from unloaded chunks, but much less often than in vanilla (1.6.4, that is, as I don't play in newer versions but Mojang did update the lighting engine in 1.14 with various bugs marked as fixed).
Otherwise, I've never seen ghost lighting be left behind after a block light source was removed unless it was already present (e.g. breaking a torch, which is which functionally the same process as far as light updates go, either just replaces a block with a non-light-emitting block), including MC-102162 (in vanilla 1.6.4 redstone ore will glow with a light level of 14 if it is next to lava due to light-emitting blocks being treated as if their opacity is 1, and keep glowing at that level if the lava is removed, but it will properly darken the entire area lit when it stops glowing).
Are you sure it is bleedthrough and not some sort of ghostlight emanating from outside? The latter is usually a bug of some sort, but I suppose could occur via slight chunk corruption, and is usually fixed by placing and removing blocks in the bright area until you manage to stumble upon the offending blockspace.