When you approach a tower of glass blocks that connects the sea floor to the surface, all the blocks light up (as with the night vision effect) instead of just that area.
MCPE-103654
Underwater lighting
Open
3
(Unassigned)
588300
Confirmed
Multiple
8.0
1.16.220.50 Beta, 1.16.210.60 Beta, 1.16.210.59 Beta, 1.16.210.58 Beta, 1.16.210.56 Beta, , 1.16.210.54 Beta, 1.16.210.53 Beta, 1.16.200.51 Beta, 1.16.201 Hotfix, 1.18.2 Hotfix
Retrieved
That actually seems pretty realistic. If you put a piece of glass in a tub of water, you can see through to the bottom, and light still shines through, even though its a bit dimmer.
But the whole sea floor lighting up, does not make sense.