Infravision

Infravision is an imperfect way of seeing by the heat signatures of 
creatures.  Most living creatures show up as heat sources, 
although some unusual creatures may absorb heat and show up 
as cold sources, while a few creatures (like undead) may have no 
heat signature at all.  While it can be used to target (by heat source) 
and follow your party leader, infravision is not sufficient to make out 
your surroundings or other fine details.  

Note: Infravision works as a kind of backup vision, it only comes into 
effect when you are blinded with your normal vision.  Thus, it is not 
toggled on or off, it comes on automatically when the light conditions 
are out of your vision range.