Understanding Nightvision

[Wexit]

I recently went on my first safehouse raid at midnight. I used a scout drone to see 15 tiles out and spot cultists outside of their vision range, and then shot at the from the darkness. This first mission went off without a hitch, so I thought I had figured out a useful tactic.

The second through fifth night raids didn't work the same way however, so now I am questioning how night vision works entirely. These missions I was being shot at from far off in the darkness - 30 tiles or more, despite being completely out of anyone's vision range and in total darkness. This happened with Church of Dagon as well as all of the others.
It couldn't have been light and there was no one close enough to serve as a spotter for the other cultists, so as far as I have been able to tell, they just have night sight greater than the 15 tiles of my scout drone.

Does anyone know in detail how darkness actually works? Are there units that have greater than the 9/10 that standard humans and Dagon cultists have?

[Mrvex]

Some enemies have better sight than XCOM troops. Especially non-humans or mutated humans.
Even baseline Dagon cultists have slightly better nightvision than XCOM.

One thing that could be causing the sudden spotting is if there are any light sources on the map, lamposts, burning bodies....
Or you are being seen by a one guy and he is working as a spotter for the rest of the cultists so your agent is being shot at from guys who work off informations given to them by the sole person that actually sees you.

Also, dont be decieved if the map is dark or not. As long as there is a picture of a moon when you arrive at the LZ, then its a night mission. Why am i mentioning this ? Because you can arrive at early in the morning, dont get the moon symbol and the map is dark af but it counts as a day mission anyway so your troops have full sight even if game doesnt look like it.

[the nomad]

When you research or interrogate a live enemy, you can click on 'info' on their ufopedia page which shows their armor and such. The enemy's night vision is written there, the unit being tiles.

[tarkalak]

Another thing to know is that when you shoot your gun, the enemies will know the position of the shooter for some turns. I don't know how many, though. So every enemy with sniper-spotter capabilities and line of fire will shoot. They will not have sight, so they will still have their accuracy halved.

The higher rank cultists usually have the sniper-spotter. For the Black Lotus, for example, their Foot soldiers and witches have sniper spotter and you will have a lot of return fire. It is still preferable to attack at night because of the accuracy mallus on them, and the enemies without sniper-spotter cannot shoot until they themselves have vision.

If you can see exactly from what tile the shots are coming you can do the same, but this is pretty hard to do.

Some enemies indeed have better night vision than 9. Aliens see like it is day.

[Solarius Scorch]

Yhe act of shooting your gun by itself doesn't alert enemies, because X-Com doesn't have a sound system (yet, heh heh). But if you hit a unit, that unit will automatically spot you, as per vanilla X-Com mechanics (which is why an enemy can turn and react when you shoot them in the back). If this unit is a spotter, then they will report your position to any snipers.
(Apologies if the above is rubbish, I just infer from my experience and bits of knowledge, not the code itself.)

As for the duration of spotting, in almost all cases it's 1 full turn.