for me darkness makes everything deeper. Things get more meaning and so do thoughts and feelings. In the dark i can focus my thoughts on things/feelings that really move me. There exists a silence just like someone killed every noise there was before.
Silence combined with darkness can really be a powerful unit giving you strength.
Talking of the other darkness,the one that is within us, for me darkness is the whole of every depressive/sad feeling like emptiness and fear, feeling lost, drifting.