Why this is an issue: This causes unnecessary lag to the light thread, particularly when doing stuff in void worlds.

From y=-1 to y=-2048 light level for skylight, as shown in debug menu is considered, but for below -2048, it always shows as level 15.

Block light is also considered, but this does not bear a large impact in relation, as skylight has to propagate all the way down.

How to reproduce the lag: get a void world. Fill in something like /fill -90 1 90 90 1 -90 stone . note lag occurs. Then, do /fill -90 0 90 90 0 -90 stone , then fill /fill -90 1 90 90 1 -90 air and then /fill -90 1 90 90 1 -90 stone . Note lag does not occur