I know there's been a lot of threads on the darkness spell, but after reading through them, I'm still somewhat confused. So here's the situation that is about to come up in my game, with items I'm unsure of bolded and numbered. Please correct anything I get wrong. (LL = Light Level, with Darkness = 0 and bright = 3)
There is a (naturally) pitch-black room. The party has both non-magical torches and magic weapons which glow (as per light, Core 468). In this room is an evil cleric who is prepared to cast darkness.
At first the room is fully dark. Then the party walks in with their two types of light sources. Assuming each player has either a torch or a glowing weapon, each player is surrounded by 20' of normal light (LL = 2), then 20' of dim light (+1 LL). Where the dim areas intersect, the light level is normal (LL = 1+1) {1}.
The cleric sees them coming, although he's still far enough away that they don't see him, and casts darkness at his feet. This creates a 20' radius of dimming (-1 LL) around him (which has no visible effect, because he's already in natural darkness, but effectively gives him LL = -1).
The party splits up a bit (torches on one side, magic weapons on the other), and approaches the area of magical darkness. Their light sources would normally start illuminating the area, but because of the darkness, they don't work as expected. The torch's +1 LL area meets the darkness's -1 LL area and the overlap remains fully dark {2}. This is immediately visible to the party as a semi-circle of darkness (-1LL + 1 = 0LL). Even if question 1 above is true, if the party had two torches side by side, the area would still be dark {1b}, because "nonmagical sources of light, such as torches and lanterns, do not increase the light level in an area of darkness." (Core 264) The magic weapon's +1 LL area acts the same way on the other side {3} ("Magical light sources only increase the light level in an area if they are of a higher spell level than darkness.").
The party approaches this strange dark area, until their brighter zones intersect it. Because of the rule quoted above, the dark area stays dark, but the rest of the radius continues being normal or dim light as appropriate {4}. The cleric has escaped out the other side of the darkness area by now.
Finally, the party torch- and weapon-bearers enter the darkened area directly. They continue shedding their light (magical and not), so outside the darkness area, there's still light {5}, but inside the spell area, it's still fully dark {6}.
Having worked through it, there appears to be no practical difference between a normal torch and a glowing magic weapon (or a level 0 light spell). Everburning torches are a separate issue which I'm not looking into at the moment.
There is a lot i like about Pathfinder
But when it comes to Light, Darkness, Magic, Non-magic, Shades of gray.... i think i like the old system better...
which was magic was magic, and it suppressed what every there was currently, within its effect. Then you only had to worry about someone casting a higher level spell, or using a Heighten spell to make a lower level spell stronger than what it is trying to beat.
Oh well, back to figuring out how many candles, light a area, as they flot down a river, after you light 50 of them, and the water spreads them out, under startlight.
Honestly, the "nonmagical sources of light, such as torches and lanterns, do not increase the light level in an area of darkness" rule is borked and has been for some time.
Consider that bullseye lanterns--which have directional beams, created by means of lenses and reflectors--exist in game. They're portable spotlights. How many bullseye lanterns do you need to focus on an area before the illumination level goes up to the next one? 2? 5? 10? 50? If you say that you can have an infinite number of lanterns focused on the same spot and the light doesn't increase at all, you're saying the world does not follow normal physics--even more crazy when you consider that the magnifying glass as listed can be used to focus the sun into a beam and light fires.
The best solution is to say that while more light sources do increase the light level, they don't do it enough that it counts as the next lighting level up until at some point the GM admits that they do. After all, logically a candelabra illuminates more than a single candle, and a chandelier should illuminate more than a candelabra, so you might as well houserule ranges of illumination for each, rather than worship the RAW like a graven image and support idiocies like saying that the grand chandelier of the Paris opera still can't illuminate more than 20 feet, meaning that the entire opera house is shrouded in darkness because obviously the chandelier is suspended more than twenty feet above the seats.
Honestly, the "nonmagical sources of light, such as torches and lanterns, do not increase the light level in an area of darkness" rule is borked and has been for some time.
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If you say that you can have an infinite number of lanterns focused on the same spot and the light doesn't increase at all, you're saying the world does not follow normal physics--even more crazy when you consider that the magnifying glass as listed can be used to focus the sun into a beam and light fires.
Well, you're conflating two things here - That rule is specifically for magical darkness, in which case it makes just as much sense to say that 20 mundane spotlights won't brighten it any more than a single mundane candle as the reverse. There just appears to be no explicit rules about how to treat stacking light sources and ordinary darkness, which is why I went with the logical result in #1 above.