Steps to reproduce
Place glowstone at Y = 319.
Set time to night.
Expected result
All sides of the glowstone are bright.
Observed result
The top of the glowstone is darker.
when placing a block on Y319 (max.) the light level above the building limit won't be there
This is a client-side bug with displaying block light. Sky light shows correctly on top of blocks at build height, and the light level at Y = 320 calculates correctly server-side (block light blocks monsters spawns on top of blocks at build height--MCPE-112682 is fixed).