Good point. But, how do you modify the light source distribution? Surely a light strapped to your backpack is less effective than one you hold overhead.The cost, as people like to put it is in the benefits/detriments of being constantly in light. You are always visible to enemies and will never surprise something. Enemies have time to prepare as a result of such light sources as well, enabling traps and the like.
Many things in D&D are abstracted. Why should this be different? Do you want characters affixing sunrod-holders to the top of their helms to create some rather silly-looking headlamps, because that's ultimately where that reasoning heads.Good point. But, how do you modify the light source distribution? Surely a light strapped to your backpack is less effective than one you hold overhead.
I guess the real question is:
Does darkness actually add anything to your game?
Without heavy modifications to the existing rules, I doubt it. The light rules as written are basically presented as a big screw to use against the PCs if they neglect to write "a light source" on their character sheet.
If you're going to go all out and actually work out where shadowy areas on a battlefield are, and actually play monsters as if they don't want to stumble about in the dark all the time, then I'd say feel free to enforce accurate usage of light sources along with it. I think such a system has the potential to add a lot to the game (ok, if you move over there with our light source, then I have concealment because I'm in the shadows from that statue, so I can hide!) but also a lot of complexity.
Using light in the Heroic tier adds a lot to atmosphere and gameplay, if done properly. Why were the alien films to exiting? Imagine how boring it would be if everyone had a massive "top down" view radius in the film...lol.
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All of this is really hard though if you are using normal paper dungeon tiles. I'd be interested to hear of any ideas anyone has. If you allow sunrods, I my opinion this actually makes it *harder* to work out light on paper; like I said I think they are there just to make the light rules "go away".

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.