The issue is not present in Java, the lighting between two of the same types of block is different and can ruin cohesion in a build. I assume this is not intentional
Steps to Reproduce:
Place a sandstone/smooth sandstone block.
Place its stair variant next to the sandstone block.
Look at the backside of the stair and compare its lighting to the sandstone block.
Observed Results:
The sandstone stair appears darker than the sandstone block.
Expected Results:
The sandstone stair appears lighter, matching the sandstone block.
Linked issues
discovered while testing
is duplicated by
Attachments
Comments


This issue only occurs with smooth lighting on, when turned off the stairs match the colour of the sandstone blocks.

The issue is also much less pronounced with brightness set to max, and more pronounced with it set to the minimum. As one might expect considering Nede Krug's comment, this doesn't affect it when smooth lighting is off.
Tested on wood stairs.

Thank you for your report!
We're now tracking this issue at MCPE-54410, so I will forward resolve and link this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
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Based on some further testing today I'm going to re-open this report as it appears distinctly different to MCPE-54410.
MCPE-54410 appears to be an issue with lighting and how it interacts with stairs and slabs which is demonstrable in that the effects of 54410 changes depending on where around the stairs and slabs torches are placed.
Sandstone, smooth sandstone and red standstone by contrast are different no mater what lighting is around the blocks.
Stairs and double slabs are darker than a full block and slabs are darker again (but this is just due to MCPE-54410 darkening it even more, with torches they match the stairs and double slabs).

This issue cannot be reproduced in 1.21.20+ because the sandstone and red sandstone blocks have had their brightness adjusted to match stairs.
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Somehow missed this when searching for this issue. Anyways, this is extremely frustrating on a build I've been working on on Realms (oof). Another user pointed out this happens with slabs and quartz as well.