Darken is a active skill for Myrddraal. It can be used at night or in "perma-dark" rooms and can be cast repeatedly.
Effects of Darken
Reduces the timerby how much? on all held light sources in room. In general, lower tier light sources (torches and lanterns) will be burn out with each darken requiring the user to hold a new light source if they wish the room to remain lit. Lightsticks and higher tier lanterns will be damaged and may burn out. Lightball will not be affected.
Historically, darken has suffered from unintended balance or coding issues in which rooms were permanently darkened such that holding a lantern did not light the room at all or issues in which the rooms light-dark toggle becomes broken such that holding a lantern or lightball makes the room dark and vice versa.
To Negate Darken
Carry spare lanterns with the understanding that the fade can cast the effect repeatedly potentially burning out your entire supply, travel with a channeler with lightball, avoid dark rooms behind doors where a fade can incapacitate the entire group while the door is kept closed, or disengage from the battle and leave. Humans are dramatically less functional in the dark and the weave essentially functions as a group blind effect as humans have reduced fighting capacity, functionality, and ability to compete in the dark.