BlackFire is, perhaps, the opposite of fire, in that it consumes the heat of anything in its attack geometry. This spell manifests as a cone from the caster's outspread hands, to a range of 10 metres. The base of the cone is 5 metres wide. Everything in its path takes the force of the spell as cold damage.
In addition, they may be afflicted by an effluvium that propagates with the BlackFire. Anyone whose eyes are unshielded during the attack will have their vision impaired. This is a morale effect. The duration of the effect is determined, in part, by the number of the initiations of the victims.
The visual impairment starts at the force of the spell, and is reduced each round by an illuminating force (i.e. a light spell) or by the force of vision that penetrates darkness. The force of the spell is subtracted every round until this BlackFire effect dissipates.
The value of the impairment is 2, so his vision is 1/2 normal. The subsequent round his sight will be free of the effluvium.