#obscuration

If you're upset about your players all having Darkvision when all you want is to make it hard for them to see, then you aren't alone. Now, I understand that it's a perfectly valid thing to have Darkvision in D&D. However, it's also perfectly valid for a DM to need to have things hidden or at least difficult to spot for narrative, puzzle, or combat reasons. So here are some simple tools that a DM can use to reclaim the night.

Understand the Rules

First of all, many people don't understand how Darkvision works in D&D 5e (myself included for a while). If everyone in the party has Darkvision and they opt not to use light while exploring a dark space, the creatures don't see things clear as day. "Dim light becomes bright light and darkness becomes dim light" is what the rules say about Darkvision. Darkness is technically still lightly obscured. Therefore, players will have disadvantage on Wisdom (Perception) checks. Their passive Perception gets -5. They are still sitting ducks for an ambush. It will likely take just one surprise attack to make players realize that while, yes, it's easier to sneak in the dark, it's also harder to see.

Not to mention Darkvision doesn't let creatures see in color. So if they choose to go this route, they may miss out on identifiers like the telling robes of a Red Wizard.

Change it Up

It's your campaign, so you can change Darkvision a bit to suit your needs.

In my campaigns, I operate under the assumption that players can't read text or see patterns on cloth if they don't have light. For instance, an elf in the dark could see a sheet of paper, but not the words written upon it. Sort of like a 3D model without textures. That may not be the way night vision goggles work, but this is a fantasy setting, so I can do what I want. It forces players to cast light or light a torch every once in a while.

Back in older editions of D&D, there was Infravision and Ultravision. Infravision could see into the infrared part of the electromagnetic spectrum, so they could detect heat. You could change Darkvision to this, meaning that they could only see heat sources in the dark. Walls would block this unique type of vision, and some creatures would be invisible (like reptiles, constructs, or undead). If players had a hot light source, it would blind the creature to other heat sources while it's lit.

Ultravision lets you see the other side of the spectrum, which doesn't help very much from a standpoint of detecting creatures. However, in AD&D it was understood that magic emits ultraviolet light. This essentially let such creatures see the influence of magic. I would stay away from this one as it nearly replaces detect magic. If you were wondering, players could have both types of vision and it was called Supravision (it also let creatures detect the school of magic when using Ultravision).

Use Obscuration

If you aren't comfortable with changing Darkvision and it's rules, you can still put creatures with Darkvision on equal footing with other species by using the rules for obscuration. 

If looking into an area that is lightly obscured, a creature gets disadvantage on Wisdom (Perception) checks and -5 on passive Perception. A creature can hide in a lightly obscured area. If looking into an area that is heavily obscured, a creature is effectively blinded. Therefore they automatically fail sight-related Perception checks, and also have disadvantage on attack rolls.

Here are some things those dark dwellers can see through just as poorly as everyone else:

Light Obscuration:

Mist

Webbing (such as the web spell)

Light Foliage

Light Precipitation

Swarms of Insects (such as the insect swarm spell)

Heavy Obscuration:

Fog (such as the fog cloud spell)

Magical Darkness

Heavy Foliage

Heavy Precipitation (such as the sleet storm spell)

Significance of Area of Obscuration and Derivation of General Expression by Method of Integration

by Gourav Vivek Kulkarni "Significance of Area of Obscuration and Derivation of General Expression by Method of Integration"

Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-5 | Issue-1 , December 2020,

URL: https://www.ijtsrd.com/papers/ijtsrd35869.pdf

Paper URL : https://www.ijtsrd.com/mathemetics/calculus/35869/significance-of-area-of-obscuration-and-derivation-of-general-expression-by-method-of-integration/gourav-vivek-kulkarni

callforpaperarts, artsjournal, peerreviewedjournal

Determination of Area of Obscuration between Two Circles by Method of Integration

by Gourav Vivek Kulkarni "Determination of Area of Obscuration between Two Circles by Method of Integration"

Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-5 | Issue-1 , December 2020,

URL: https://www.ijtsrd.com/papers/ijtsrd35863.pdf

Paper URL : https://www.ijtsrd.com/mathemetics/calculus/35863/determination-of-area-of-obscuration-between-two-circles-by-method-of-integration/gourav-vivek-kulkarni

ugcjournallist, listofugcapprovedjournals, researchpublication