Same thing again.

[Lyris-Lyanther]

What is the light problem I keep seeing people talk about?

[Vidu]

What is the light problem I keep seeing people talk about?

In Shadowbringers we visit the first shard, the birthplace of the Warriors of Drakness we met in Heavensward. If you recall their story you know that they were to good as heros in their world and tipped the balance heavly in favour of the light, thus causing a flood of light that destroyed most of their world and now threatens to wiped out the little thats left.
Because of that the first has no night - its always glaringly bright, which is obviously a problem (wait and see for yourself when you reach those areas - it almost hurts your eyes and feels weird to look at your Eorzea-time and realise that its still extremly bright despite it being past midnight).

...I dont want to spoil anymore, though. But the light problem is basically the flood of light that Minfilia went to stop at the end of Heavensward.

[Zarabeth]

Sometimes I fel like I'm the only one who actually enjoys hunting for aether currents heh.

Newp. I get mine too.