Why do we come up with houserules? Because there’s some kind of problem. Maybe not everyone sees it as a problem, but that’s oftentimes just because people have learned to live with it and be complacent with a deficiency that could be fixed.
How do we come up with houserules? We 1) identify the sources of the problems and 2) identify the results we would like to see instead. Creating a rule is creating the “cause” in a cause-and-effect relationship. In order to know what cause you should aim for, you need to know what effect you’re after.
What do we do with houserules? We test them out and explore their full implications. We look for vulnerabilities that could be exploited. We try to break them. We consider some unintended consequences. We try to think of ways it could interact with other game elements. We playtest it. We adapt it. We eventually figure out the best ruling possible. Maybe it’s a refined version of the houserule, or maybe it's the RPG’s original ruling after all.
What’s the Problem?
Like, what is the reality of darkness for those who do bother with it? They have to fuss about keeping track of the 20’ radius light of the enemy’s torch and the 60’ cone of light of your cleric’s bullseye lantern plus considering that the merchant you’re protecting has the hood lowered on his own lantern to shed dim light in 5’ or whatever. That practically requires you draw it on a grid, except that if people move on their turn then their light radius moves with them so you’ll have to erase and redraw every round. So instead you'll want to have a ruler on standby or make one of those pre-cut cardboard/plastic circles, but those are a hassle too and they tend to knock over other minis and terrain. So then you probably use some software to simulate it in a digital game, or... actually, just say fuck it and assume that practically the whole battlefield has some light in it at that point, because honestly how big could the room even be? Most dungeon rooms can be adequately lit up by one hooded lantern anyway.
But darkness could be a potent game element with the right system. We can imagine darkness being this huge challenge for scared adventurers to overcome. The fear of darkness is very powerful, and the disadvantage of not being able to see your opponents should be serious. We like to find ways to put our players into positions where they have to think carefully to get out alive and not make things worse for themselves. We like to add dimensions to combat that can be simple and yet have huge consequences in how people operate. We like to force players to work for their achievements and be faced with tradeoffs.
Is your game bad for not having good darkness rules? No. Almost all groups are getting by just fine without it, so it’s clearly not crucial. But can you see how it could be something that might improve your game? Don’t you want the Underdark to actually be dark?
What’s Causing Those Problems?
If you’re in bright light, those effects go away. If you’re in dim light, then you merely have disadvantage on sight-based checks but are otherwise operating entirely normally. Even your attacks remain unaffected in dim light. You could get rid of dim light if you want darkness to be a bigger problem, but I don’t much care for that solution. I like dim light. It has its own uses.
If attaining light is trivial, then you could just raise the price. But then the challenge is really about earning money. You could force the players into the Underdark for months until they’ve run out of lamp oil, but then they just don’t have any solution. That’s more of an all-or-nothing problem vs. solution.
If tracking light is a pain, then why? Because there are differences between different sources of light. They each have their own range and duration. Their full range isn’t very intuitive so you usually need a visual way to help illustrate how far the light goes. Keeping track of time in a dungeoncrawl is annoying (already a lost art in the modern mainstream of D&D), so tracking remaining light-time is just more annoying bookkeeping.
Looking for the Right Effect
And this was when I realized that sticking to only allowing to your players the more historically-grounded candles is a pretty significant way to make light and darkness matter in your gaming.
The way to address the problem with darkness is to pull back on the power of light.
Logistical concerns? Conveniently, an Exploration Turn in a dungeon lasts 10 minutes. The DM is already rolling for random encounters every 10 minutes anyway, so somewhere on your character sheet, maybe near equipment, have 6 boxes you can check off to determine how much light is left in that candle. If it falls or gets blown out or something, the rest of the candle’s life is wasted and you have to start with a fresh one, erasing your checks. Or maybe instead of checking boxes, once every Exploration Turn you can roll a d6, extinguishing it on a roll of 1, because you prefer rolling dice to bookkeeping resources (which is fair. Just understand the candle might last literally only 10 minutes, or maybe like 3 hours). I personally use the die roll method in my own group.
Ease-of-use at the table? This removes all of the normal inconsistencies. In a combat scenario, especially with a grid, it’s easy to visualize light if you can always remember “within 2 squares of that guy,” maybe putting a little token underneath the miniature of anyone carrying a light source. It sounds harsh, but it’s actually more realistic, too. In reality, torches and oil lamps just don’t offer that much light, and are mostly the same as a candle or candle lantern. You can look it up, it's actually a well-documented misconception we've inherited from popular media: torches and lanterns kinda suck. Maybe you can give torches a smelly property or allow oil lamps to last longer or something if you really want to distinguish between light sources. But otherwise, we have all PCs who are holding a light source just place a small token underneath their miniature so every other PC knows, “gotta stay within 2 squares of the mini with the token.”
Accessibility for PCs? Light is still fairly cheap, but now it’s a money-sink they’ll want to regularly invest in just because 1) it has such a short duration that you'll constantly be running out, and 2) it’s suddenly so much more important. Because no light source can reach 60’ in all directions anymore, the light offered is less directly powerful. But because the small amount of light that you do get makes a huge difference, it becomes a priority.
What Other Changes Should Accompany This?
You should also ban or nerf magic items that grant light. I know you can say “well 30’ of light would be extra good in this system!” right? It seems tempting to break the consistency, but do not do this. All of the strengths of Advanced Darkness are completely undermined if you ever introduce an exception. It's crucial to standardize the range of all light sources, lest you 1) disrupt the realism of the fiction (not super important I'll admit but it's there), 2) completely undo the convenience of feasibility and mentally visualizing things, and 3) nullify the challenge of darkness entirely. If you give the PCs a 60’ radius of light then in a dungeon that’ll probably fully light up whatever room you’re in anyway, so that’s functionally a “light the entire room” spell. Don't get me wrong, it's good for players to have resources and abilities at their disposal which make challenges easier, but it's bad if they trivialize challenges entirely. That's a gameplay killer. Give your light-based magic items weird properties instead, like revealing invisible things or only granting light to the wielder or whatever. By nerfing all light, it creates more meaningful decision-making with employing light sources. You’ve added to the cost of the decision.
Pertaining to player choices involving light, I offer the following: while normally you have disadvantage on sight-based Perception when in dim light or are effectively blind while in darkness, that doesn’t apply when you’re looking at someone who is themselves holding a light source amid the darkness. You treat them as not being obscured at all since they’re standing in a pool of light. In fact, they have disadvantage on their Stealth against sight-based Perception while holding a candle. It’s super easy to see someone carrying a lantern in the dark, which makes them vulnerable to ambushes. This goes both ways, of course. The PCs are vulnerable.
I don’t think a lantern should be able to attach to a belt. Force the player to use a hand. Make them keep track of candle supply (if your encumbrance system is really limited on equipment slots then consider letting 8 candles take up 1 slot, or maybe don’t even have your light source take up slots). When they want to take a long rest, if they want to keep a campfire or candle lit all night then they have to consider that enemies can still see them (with advantage!). If they choose to sleep without one and end up being attacked in the night then they better be ready to light something quick when the battle starts.
Remember the senses and how they get affected. Dim light gives disadvantage to Perception checks, so when you note down everyone's Passive Perception score, make sure to write it twice: Bright Light = 10+bonus and Dim Light = 5+bonus. Or just remember to mentally subtract 5 when you refer to their Passive Perception.
If your game has darkvision that doesn’t already work this way, then I recommend tweaking it so that it only applies when the creature is outside of a light source. Essentially, your dwarf eyes have to adjust to the darkness by stepping outside the light. This way, when you have humans in the party who need that lantern, it puts everyone on the same page. Darkvision is useful for if the elf scouts ahead, or if you have an entire group of people with darkvision, like a squad of drow. But even they and many other natives of the Underworld, when not intending to sneak, prefer to still have a light source so they don’t see at disadvantage. But basically, darkvision takes a round to kick in. On the turn when you leave the pool of light, you have normal vision until the start of your next turn, at which time all the darkness turns to dim for you. When you are back in a pool of light, it isn’t until your next turn that you lose darkvision bonuses. No, I don’t give some kind of penalty when returning to light because “it’s so bright it hurts your eyes” or whatever. I’m not that much of an asshole.
How Does This Change Things for the DM?
When narrating encounter spaces and dungeon areas, you’ll find that you are giving out much less information for free. Almost everything the PCs learn will have to be things they seek out themselves, and that means they need to formally declare things like, “I go over to the southeast corner of the room. What have I found?” instead of you just describing the whole room upon entering. In order to get used to this, you’ll probably stop describing the room as it truly is or how your map shows it to be and instead start picturing everything from the first-person point of view of your players when they enter the room. If you run pre-written modules, you’ll probably have to abandon a lot of the boxed text because it doesn’t account for this. Oh well. Those suck, anyway. This is actually a really interesting way to narrate the story and makes you think about the adventure very differently. It’s also a great exercise while designing an adventure, because it forces you to get into the heads of the players. So many DMs are constantly surprised by how their players interpret things, but you need to consider things from their perspective. Sometimes literally.
To make the role of darkness more meaningful and threatening, as well as to make light sources easier to implement, the solution is to pull back on the power of light.
Firstly, this is supported by realism (for whatever that's worth). In pre-industrial Europe, people relied on candles (sometimes set into a lantern) and maybe torches, both of which are extremely weak in their range and duration of light.
Secondly, this is supported by the needs of feasibility in gaming. By having all light ranges be so small, it's really easy to mentally visualize it on the grid, because it's just "everything within 2 squares of the mini." You never need to draw the radius because you can always see it in your brain. Instead, you can just place a token under the miniature with the light source.
Thirdly, this is supported by its effect on challenge and gamification. The penalties of being in darkness (heavy obscurity + the added detriment of disadvantage on attack rolls) are pretty severe, but they can't be made relevant as a meaningful challenge in a combat scenario if the entire room is always lit up. The majority of a medium sized room should be in darkness, so that the players' options for where they can take the fight are limited to small islands of light. It forces players to cluster up and it gives better mobility to Underworld monsters/NPCs with darkvision.