Alright, so I've read over how the spell is described as working. I'm still confused as to how it works.
As written it either reduces the light level by one except that nonmagical light sources that originate inside it might as well not exist for light levels, while ambient light sources outside its radius still affect its light level. And Spells lower level than it are treated the same way.
Or it ignores any nonmagical light source as well as well as any light spell lower than itself and always makes its area pitch black except where higher level spells are involved.
And in either case darkvision functions normally, its cast on an object and therefore mobile, only more powerful light spells counter it and even then only to a limited extent.
If the second interpretation is correct, my concern is that it is in danger of becoming a cheese spell for casters with darkvision... for example any of them who bother to have the spell. In addition, why bother listing the fact that it decreases the light level at the beginning of the spell as if that's the really significant part of the spell? Just say it create a globe of darkness and then list the effects of higher level light spells later.
Not only is does the spell allow a caster (and friends) with darkvision 50% miss chance at no penalty for 10 min per level, but it also makes it hard to solidly target anyone inside it with a melee or ranged attack or spell unless you use area of effect spell, since its an area of solid darkness that grants anyone inside it total concealment.
This seems to be a simple, deadly and horribly unbalanced combination that allows, say, a half-orc cleric with a darkness spell to horribly slaughter anyone in his path (since there are also alot of other penalties applied to a blinded target, ie anyone in total darkness) who does not happen to have a daylight, continual flame, or darkvision spell. Plus the cleric can grant it it any friends with darkvision who stay in the radius the benefits at no penalty as well.
Really, what I'd like is a response from the Paizo team so that I can get what their interpretation of the spell is supposed to be, and maybe reasoning too.