I am using clockwork for custom day night cycles, its nearly always night :p however the whisps don't glow it seems. if you need more info on all mods i use lemme know

Did you migrate save file from 0.16, or is it an otherwise old save file?
I can think of why that might happen when updating from really old version, but even then should be only for one current night, and be fine on all subsequent ones.

you are right, i think changing day nighttime cycles caused some troubles :)

Uh, but I didn't mean that at all, was only asking about whether it might be a save file from old game/mod version.
Do you say that because disabling that mod fixed the issue?

Changed cycle should only affect this if it somehow prevents lights from enabling at dark time in the whole game, which don't think should be likely, though to be fair, haven't checked with Clockwork mod myself.
That mod works by changing number of game ticks per day, so you get same in-game nights with it, just at different times.

Its a new save but I meant to answer this part you said: "but even then should be only for one current night, and be fine on all subsequent ones."

It does work fine now. only after changing the day//night cycle it goes wrong the first time. I have been messing around a lot in my new game with day//night cycles. but now that it is steady again it works great!

Hm, still weird, sounds like an engine quirk wrt how lighting effects get enabled with altered cycles.

Meant "should be only for one current night, and be fine on all subsequent ones" wrt migrating from old pre-0.17 mod version btw, where "lights" were made by creating explosions under wisps every few ticks.
In 0.17 new API have been added where you can just attach light to entity, so that's what newer versions do instead, but if you load save from old mod made during night, wisps that are still around won't have that light attached, but be gone by the daytime anyway, and all new ones will get it.

Thanks for reporting it, should be easy to reproduce and might be worth a look at when exactly lights bug-out like that.