A Lux is a demon which is derived from the life essence of fauna. Unlike their corrupted form- a Mud Beast- they are not innately malicious.
A Lux is made from the souls of animals which have condensed into a singular entity. They are primarily guided by instinct and are very emotional, skittish creatures. They account for most demonic possessions, which either occur by accident as a result of a Lux fixating on a particular animal, or because a witch has bound them as a familiar. Many cryptid myths stem from Lux- whether their true, summoned form was spotted, or the bodily distortions that occur in a possessed creature.
Most Lux lack higher consciousness, so they are easily manipulated in a ritual situation, but are nonetheless volatile and disoriented when summoned. Because of this, most covens have their shrines surrounded by metal bars. When safety precautions are taken, Lux are generally harmless, making them the only type of demon that most witches find acceptable to utilize. Still, many occult practitioners have made the mistake of allowing a Lux to mimic their humanity, resulting in the demon's corruption into a Mud Beast.
The reason why Lux are easily disoriented is that they do not experience time in a linear fashion, which makes them a valuable asset for the art of divination. Relics are often harvested from Lux to refine this power. Once summoned as a familiar, Lux seem to become much more grounded in the present.