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.