हृदय में परम ज्योति : The light in the heart
Janaka asked:

‘When the sun has set, o Yājñavalkya,
when the moon has set,
when the fire has gone out,
and when speech has ended:
what light is there for a person?’

Yājñavalkya said:
‘Self-nature alone is his light.
It is by this light, by the ātman that
he sits, goes out, performs his work, and comes back.’
‘Which is this ātman?’ Janaka asked.

Yājñavalkya said:
‘Puruşa consisting of consciousness,
in the life-forces, within the heart, the inner light.’

- Brihadāranyaka Upanishad : 4.3.6

~ Daily Vedanta - दैनिक वेदान्त