Next scenario:

• A big room 200 feet long. No light at all.
• A human player without a torch.
• A human NPC with a torch providing bright light in a 20-foot radius and dim light for an additional 20 feet.
• They are 170 feet from each other.

Now some doubts:

• Can the human player without a torch see the NPC due to the NPC carrying a light source? I think so. We have an example of this situation in "Darkness and light", DMG, p. 104.
• Can the human player make a ranged attack without disadvantage because he/she can see the NPC? Probably yes, and maybe with advantage?
• Can the human NPC with the torch see the player? I don't think so due to the light radius provided by the torch.
• Would the human NPC make a ranged attack with disadvantage because he/she cannot see the player? I think so.

Please, let me know if there is some interesting post here in DnD Beyond about similar questions to this one.

Okey so,

1. "Can the human player without a torch see the NPC due to the NPC carrying a light source?" Yes, and technically they can both see each other if the NPC makes a good perception check.

2. "Can the human player make a ranged attack without disadvantage because he/she can see the NPC?" Yes, however, to get advantage they would need the NPC to fail their perception check or go into the darkness and hide.

3. "Can the human NPC with the torch see the player?" As stated in number one, he can if he rolls high enough on perception.

4. "Would the human NPC make a ranged attack with disadvantage because he/she cannot see the player?" If they fail the perception check then yes. Otherwise, no they could roll a normal attack roll.

This is my answer for it. Correct me if I made a mistake in my logic.

So I just realized that my dumb brain thought that the 170ft obviously meant that their 30ft away from each other. My math brain was on.

1. Yes
2. Yes
3. No 
4. Yes

It's two different things really, that enable Stealth. Game elements that specifically work on invisible creature don't work on one in darkness and vice versa. For example a human able to See Invisibility wouldn't see a creature in darkness, nor is someone  with Darkvision can see an invisible creature in darkness.

Thanks guys. There is a consensus then, great!

I have a new question.

No torches at all so now we have darkness in the room. If neither the player nor the NPC attempted to Hide by making a Dexterity (Stealth) check, are they aware of each other in order to attack or at least notice the presence of another person in the room? Does this awareness perhaps depend on the range and 170 feet is too much?

I guess it's up to the DM and each scenario, but I'd like to know your opinion.

Quote from tarodnet >>

 

No torches at all so now we have darkness in the room. If neither the player nor the NPC attempted to Hide by making a Dexterity (Stealth) check, are they aware of each other in order to attack or at least notice the presence of another person in the room? Does this awareness perhaps depend on the range and 170 feet is too much?

I guess it's up to the DM and each scenario, but I'd like to know your opinion.

 It would depend if as DM i determine they're within each one's Perception range and that it is the distance i want the encounter to start from. 170 feet is a bit far to me but they most likely would hear each other out in some way if it's the case.

the DM figures out where the adversaries are--how far away and in what direction.

In general, if a human PC meet another NPC one in darkness without any attempt to be stealthy whatsoever, then they notice each others and know their location despite being effectively suffering from the blinded condition when trying to the other in such heavily obscured area.

If neither side tries to be stealthy, they automatically notice each other.

If such is the case, then i would follow the Combat Step-By-Step and have no one surprised.

1. Determine surprise. The DM determines whether anyone involved in the combat encounter is surprised.
2. Establish positions. The DM decides where all the characters and monsters are located. Given the adventurers' marching order or their stated positions in the room or other location, the DM figures out where the adversaries are--how far away and in what direction.
3. Roll initiative. Everyone involved in the combat encounter rolls initiative, determining the order of combatants' turns.
4. Take turns. Each participant in the battle takes a turn in initiative order.
5. Begin the next round. When everyone involved in the combat has had a turn, the round ends. Repeat step 4 until the fighting stops.

@Plaguescarred while reading the new DMG, I remembered this thread I created some time ago and your last reply. It was a nice surprise to see this table :)

TarodNet Thank you for sharing this, you must have Advantage  to Intelligence (Investigation) check to find obscure information in books as evidenced by all the valuable findings you share :)

Investigation

Intelligence

Find obscure information in books, or deduce how something works.

Quote from Plaguescarred >>

TarodNet Thank you for sharing this, you must have Advantage  to Intelligence (Investigation) check to find obscure information in books as evidenced by all the valuable findings you share :)

Investigation

Intelligence

Find obscure information in books, or deduce how something works.

 Hahaha, thanks mate! :D

I'm so glad I can share the interesting new stuff I'm discovering in these books with the great people (like you!) here on the forums.