Tatah ksiyate prakasavaranam (II/52)
Tatah = then (after the practice of Pranayama); ksiyate = (is) dropped; prakasa = light; avaranam = coverage.
Then there drops the cover of light.
Basically all of us are divine (divya), full of effulgence. The root of word divya and deva (god) means "that which shines". We, the descendents of goals, are full of light. But alas!, due to ignorance, due to samskaras, due to materialistic indulgence, we suffer. We forget our true nature. We get stressed and depressed and diseased. The flow of vital energy (prana) gets obstructed and we plunge in self-created darkness. A thick layer covers our divine light.
But this is not a total permanent loss. This is like bright sun light covered by clouds. As soon as the powerful wind disperses heavy clouds, the light of the sun shines forth in all its glory.
Similarly, with the practice of pranayama, with the purification that takes place in the channels of our vital body (pranamayakosa) all the clouds inside disperse and the inner divine light shines forth.
This inner light manifests at physical level as the lightness of the body (relaxation of muscles resulting in agility), at mental level as the light of Buddhi (wisdom) that brings creativity, sharp intellect and stability of emotions and at spiritual level ever expanding peace and bliss (Ananda), the ultimate goal of human life.