I am homebrewing a post-apocalypse style world for D&D 5E, intended to be a mashup of Mutant Year Zero and D&D 5E. Thematically, one major point is that the world has been thrown into a perpetual night. I want this to matter to the player characters, and be central to problems they face. That means more emphasis on managing light sources and that special forms of vision that bypass darkness should be exceptional.
I'd like to alter the standard playable races with darkvision, replacing it with low-light vision (the ability to see normally in areas with dim light), plus some compensating factor, which I will probably choose thematically for each race. The goal is that these races should still be solid choices, as valid as before, but that they don't overshadow (no pun intended) races without darkvision due to the setting.
I am not quite sure what the downgrade darkvision -> low-light vision is worth in terms of reasonable compensation from an extra race feature. A proficiency? A known language? A situational bonus? I'm guessing that it is around this level in a normal setting.
In the setting, areas with dim lighting will be a very common adventuring environment (basically outside at night on 50% of nights), so low-light vision is still a noticeable benefit. Perhaps this fact means that I should not need to compensate anything? As despite the fact that I am strictly downgrading the ability, in the setting the new ability will be relevant a lot of the time, perhaps just as much as darkvision would be in most other settings.
I have seen the question What would happen if I removed darkvision? and that helps me understand that removing darkvision entirely makes for a workable game. However, I don't want to short-change players choosing a Dwarf or Half-orc PC at the start of the game. I will of course be sharing homebrew changes and setting details before play starts . . . so this is more about having players who would naturally choose, say, a Dwarf, feel that the race was just as viable as in any non-homebrewed setting.
Please note I am not asking for suggestions for replacement abilities - I will decide those. What I am struggling with is how to pitch the power level. Too low and I may have nerfed half the playable races, too high and I have made them too good.
Advice along the lines of "the standard race design suggests racial darkvision is equivalent to a resistance or other conditional Advantage" would be ideal.