I am creating a map that simulates subnautica in minecraft, and i´m having problems because no matter how deep i build the water is not dark at night time, i tried using the blindness effect but it does not you regulate the range as the level of the effect makes no difference at all.
There is no feature to do what you want (I assume you want some kind of "super-blindness" with which you see nothing), but you can abuse a bug for this: https://bugs.mojang.com/browse/MC-4647
Simply give the player both blindness and night vision at once and everything will turn black.
You could also achieve a similar result by setting your brightness setting extremely low, but that would require editing
options.txt and restarting the game every time you want to go outside the normal range that is possible in the game settings. In case you still want to do it, the entry is "