Vishoka va jyotishmati: a calm, unruffled, joyful state free of anguish, or clarity and luminosity. As always, Patanjali is terse and mysterious, and we rely on his commentators such as Vyasa to elucidate.
From Pandit Tigunait, the spiritual head of Himalayan Institute (the background of my first mentoring teacher Sarah Wilson):
A state of consciousness free from sorrow and anguish, and infused with inner light, also anchors the mind to the peaceful flow free from thought constructs.
So, resting our mind on the breath, and attending to a natural flow of senses, calms and steadies the mind, allowing a clear, luminous flow of awareness (who we really are) to make itself known. These practices help our brain to function at its best - without the distraction of a constant stream of narration and thought ripples, receptive and responsive to the calling of the moment.