Just doing another run through with a group of all dwarves, to try out some ideas. One thing I'm noticing is that during a fight with some Soraks after the first keep, I'm fighting at disadvantage because "the enemy is unlit". Since I have a couple of humans in tow, my cleric cast a light spell on her warhammer, so it's providing some light for the area. She's not right up in melee, so my understanding is that it would be considered "dimly lit". Which, for darkvision, means the dwarves would fight as though it were fully lit. But they're still fighting with disadvantage, specifically due to lighting conditions.
From players Handbook..
DARKVISION
Many creatures in the worlds of D&D, especially those that dwell underground, have darkvision. Within a specified range, a creature with darkvision can see in darkness as if the darkness were dim light, so area of darkness are only lightly obscured as far as the creature is concerned. However, the creature can't discern color in darkness, only shades of gray.
LIGHT RULES
VISION AND LIGHT
The most fundamental tasks of adventuring noticing danger, finding hidden objects, hitting an enemy in combat, and targeting a spell. To name just a few rely heavily on a character's ability to see.
Darkness and other effects that obscure vision can prove a significant hindrance. A given area might be lightly or heavily obscured. In a lightly obscured area, such as dim light, patchy fog, or moderate foliage. creatures have disadvantage on Wisdom (Perception) checks that rely on sight.
A heavily obscured area - such as darkness, opaque fog, or dense foliage - blocks vision entirely. A creature in a heavily obscured area effectively suffers from the blinded condition.
The presence or absence of light in an environment creates three categories of illumination: bright light. dim light. and darkness.
Bright light lets most creatures see normally. Even gloomy days provide bright light, as do torches. lanterns, fires, and other sources of illumination within a specific radius.
Dim light, also called shadows, creates a lightly obscured area. An area of dim light is usually a boundary between a source of bright light, such as a torch, and surrounding darkness. The soft light of twilight and dawn also counts as dim ligh1. A particularly brilliant full moon might bathe the land in dim light.
Darkness creates a heavily obscured area. Characters face darkness outdoors at night (even most moonlit nights), within the confines of an unlit dungeon or a subterranean vault. or in an area of magical darkness.
Furthermore, if you hold ALT when looking at a torch or a light spell, it will show you the area it can luminate in full and dim light. I found this out in the game as well, I had to change my play style a bit to work with the light levels. I did notice the enemy mobs do make some "amazing" rolls when attacking at disadvantage in dim light.
But per the 5.1 SRD (and the pbh), dim light doesn't impose disadvantage on attacks. I was assuming it was bugged, but perhaps it's a weird creative choice.
I'm hoping it's a bug and not a feature. Was very disappointed my darkvision characters were just as hampered at night as my non-darkvision characters.
I actually asked about it during in the original demo. The basic gist is:
Attacking a target that is considered to be in Dim Light for a character imposes Disadvantage
So for creatures without Darkvision, that means any target in Dim Light or Darkness.
For creatures with Darkvision, that means any target in Darkness (because it is considered Dim Light out to a certain range). They roll regular against any target actually in Dim Light.
Essentially, that means characters with Darkvision have certain ranges and levels of lighting where their extra sight is beneficial and it makes paying attention to Lighting way more important than in the tabletop game. Play a Rogue without Darkvision and then one with Darkvision and notice the huge difference in how often your Sneak Attack gets triggered.
The whole lighting system is intentional. Personally I don't like the way it's implemented, and feel it is too punishing. Fortunately the game is still in development and there is time/ability to modify this if that is the desire of the devs. That being said the below thread specifically address your concerns.
https://forums.solasta-game.com/forum/ruleset-differences-with-dd-5e
Question answered, locking the thread!
That being said feel free to make a thread in the suggestion forum if you want to discuss about the topic in more depth