This spell darkens the room you’re in somewhat more than the basic darkness spell and lasts about 1 minute per player level. It lasts a long time, but if you need to use this spell regularly the best practice is to carry a handful of nullium nuggets around instead.
The ingame help reads:
No saving throw. Casting time: 3 rounds. Type of spell: neutral spell. Affecting stats: wis. Cast type: control. Spell point cost: 21. This spell summons a circle of darkness. The duration is dependent on the level of the caster. To dismiss the darkness, just touch it.