'Yagnavalkya,' he said, 'what is the light of man?' Yagnavalkya replied: 'The sun, O King; for, having the sun alone for his light, man sits, moves about, does his work, and returns.' Ganaka Vaideha said: 'So indeed it is, O Yagnavalkya.'

In plain words: Janaka asks what gives a person light. Yagnavalkya says the sun, because by its light we sit, move, work and come home. The king agrees.