If this has already been presented elsewhere (and it most definitely must have been), let me know. This presumes you are using a Move stat from some version of old D&D.
The Rule
You use Basic Encumbrance (you don’t track coin or unit weight, your Move is dependent entirely on you using armor or “a significant amount of treasure” as determined by the referee). Treasure, in this context, is tagged Careful (hence why your Move rate drops when you are carrying treasure: you are paying attention so as not to drop it). Besides treasure, light sources are tagged Careful. Therefore, your Move rate is based on whether you use armor and whether you are carrying something Careful (treasure or a light source).
The Rationale
The issue of light management is tricky. Since neither coin weight nor Basic Encumbrance track miscellania in detail (all miscellania is considered 80 coins and BE doesn’t consider it at all beyond Referee discretion), nothing besides money and somewhat arbitrary declarations by the Referee prevents the party to stock up on torches. For the first few adventures, with all the hirelings sucking up whatever few coins the party gets, that’s not an issue. It becomes later on since torches aren’t an effective money sink once you got some reasonable treasure, not to mention magical light sources eliminating that entirely. The option of ignoring the 80 coins rule and tracking item weight individually is not viable because almost nobody wants to do that shit, for excellent reason.
This is not a bug or feature depending on table preference. Some may deliberately want light management to stop mattering with time to represent the PCs progression into heroic figures. Others who want it to still matter may use different inventory such as slots. Others have zero problem making calls regarding how many objects someone can reasonably carry while guaranteeing that ruling doesn’t diminish the party’s tactical freedom.
I prefer to offshoot stuff I don’t want to discuss to simple rules so I can focus on what actually matters to the game enough to discuss it in-depth. The rule above is my provisory solution. It keeps resource management of light away from the specific quantity of torches available (although someone can still track it if they want) and towards party speed, so it doesn’t matter how much you spend or don’t spend on torches. You may even set an amount of coins the party must pay to have an abstract amount of torches for that expedition, whatever. What matters is that the group is advancing more slowly because of torchbearers, which influences both your exposure to danger, the choice of who is wearing armor and who is carrying light, and the Pursuit rules used.
It doesn’t change the encumbrance system or adds many rules on top of it. I just used what’s already there (carrying treasure as an abstract idea changes your speed) and included light on that relying on the fictional justification we use for that rule anyway. It’s reasonably minimalistic.
You can get granular with it of course, but in general the simplest way to adjudicate it is: someone can’t be carrying treasure, light and armor simultaneously. You have to make distribution choices. Finally, you can apply it to magic light too if you want, imagining the character is carefully directing that light for exploration. Being able to carry a shield while carrying the sparkly magic sword is beneficial enough. Or maybe the appeal of magic light is one character at least not being encumbered by carrying a torch. Your choice.
This may work even if using rulesets in ways that don’t focus on acquiring and carrying gold. Do you get XP for exploring or something else, like going down the dungeon to retrieve a prisoner or kill a monster? You still have a reasonably tactical way of tracking encumbrance without getting granular. You play more sword-and-sorcery where extra granularity to encumbrance feels off genre? There’s a hopefully simpler way.
Most noticeably, it doesn’t require me to change inventory in any meaningful way besides treating light as treasure for mechanical purposes. It’s similar to ItO’s Bulky tag but baked in traditional D&D Move rate so whatever house rule I imagine for that, or whatever game with strict movement tracking I run, works with it.
Roll to Doubt 
Light is heavy. Got it…
Jokes aside, seems like a good way to roll it all together into one rule, fewer things for the players and DM to think about, and worth a bit of tactical thinking from the players.
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