Unlike Plato's myth of the cave, in the Jewish perspective, light is not elsewhere: It is within reality.
It operates poorly because its particles are poorly oriented.
In the Alter Rebbe's view, the world is not a place of shadows and darkness like a void.
Rather, it is poorly lit.
The floodlights–the sparks–shed light in an unstructured and diffuse way, and we need to bring them together and focus them correctly to produce a single beam of light.
This separation is, however, far from being radical and complete.
Light and Darkness, Good and Evil, are in constant interplay, and one of the functions of exile is in fact to separate them.
In all his writings, the Alter Rebbe defines darkness as a lack of knowledge and stupidity.
Darkness is not a separate essence; there is no Manicheism or combat between darkness and light.
What happens is simply that the part that knows is combined with the part that does not know.
Actually, this is not a mixture of positive and negative, but rather of conscious and unconscious.
Because of their unconsciousness, the unconscious parts can even harm themselves.
This is precisely what happens in biology.
Certain cells "forget" their function. and although they cannot be termed completely bad, they start to act in the wrong direction.
Instead of contributing to the normal functioning of the system. they destroy it.
–Rabbi Adin Steinsaltz
From The Seven Lights by Rabbi Adin Steinsaltz