Wow, that is pretty huge design flaw there.
Quick testing, model situation: Alien can be seen by one soldier further than 9 tiles away only because its illuminated by personal light of another soldier that actually don't see this alien. If you get into this situation with light off and than turn if on - it wont update - you wont see that alien. On the other hand, when you turn the light off, you still see the alien as if it was illuminated. You can update by turning around, but thats not how it should be. Also aliens with modified nightvission suffer the same problem - and they are not that kind to update their FOV by turning around before frying the soldier with plasma.
When setting the light on or off a recalculation of FOV must be done for all soldiers (and with OpenXcom Extended even for all aliens) or else you will get into weird situations. This should be done even in main OpenXcom build. I will post a bug to feedback forum later.
But for the diferent nightvision values to work correctly this have to be modified further. My suggestions:
1) Forcing the lighting to be on all the time but let the ruleset decide if the armor is glowing or not (also applicable for aliens so you can make glowing ones).
2) Make the personal lighting toggleable soldier by soldier. And costing TUs to turn on or off while also provoking reaction fire. It would still benefit from ability to define if the armor light is on by default or not - you don't want your sneaky soldiers to give out their position in first turn. (This would probably need some new GUI for devices that don't have keyboard like android tablets)
3) Make the default glow intensity lower than 9 to be sure that nightvision rules will be used. I dont know if the light in X-Com is additive so a tile illuminated by two sources (like a soldier and flare) would have light intensity of highest value or both values added toghether.
Alternativally combination of points 2 and 3 - light is toggleable on soldier by soldier basis and it switches between daylight intensity and nightime intensity. So even when the lights are off its not pitch dark everywhere. Or even better - have ability to set if the armor have toggleable light, if its on by default, what is light intensity when on and what is light intensity when off.