Searching through the FAQ about the Darkness spell I found the following:
Darkness: Can adding additional sunrods to the area of the spell increase the light level?
No, sunrods can never increase the light level of an area of darkness because they are not magical sources of light. In such an area, it automatically defaults to the ambient natural light level (the light level from natural sources, such as the sun, moon, and stars—not torches, campfires, light spells, and so on), and then reduces it one step.
I don't understand the logic behind this. What counts as a natural source? Only starlight? Is a lava stream natural light? What if that lava stream starts a fire or lightning? That is a light source as natural as it gets, but it is also the same thing as a campfire.
I have seen that there are other threads about the spell, but I didn't find any proper answer to this question. I hope you can help me out, what makes light natural/ambient light?
I think the intent is that darkness makes dim light if you're in sunlight, or darkness in anything else.
I also think that it was poorly worded and far too ambiguous.