Two more questions:
Do flashlights make it easier for the enemy to see you?
Is enemy human night vision shorter than day vision?
In addition to what Solaris said above.
Note that each suit has an ambient lighting that illuminates your agents and it is set ON by
default. If you want to stay in the dark you should switch it off by pressing "L".
The ambient lighting is on by default every time you start or load a mission.
You can also see the exact night vision in the "Stats for Nerds" in the enemy's combat analysis or your armor's Ufopaedia pages.