Here is the Source of this Verse from Brihad-Aranyaka Upanishad
असतो मा सदगमय ॥ तमसो मा ज्योतिर्गमय ॥ मृत्योर्मामृतम् गमय ॥
Meaning:
'Lead me from the unreal to the real! Lead me from darkness to light! Lead me from death to immortality!'
Now when he says,' Lead me from the unreal to the real,' the unreal is verily death, the real immortality. He therefore says, 'Lead me from death to immortality, make me immortal.'
When he says,'Lead me from darkness to light,' darkness is verily death, light immortality. He therefore says, 'Lead me from death to immortality, make me immortal.'
When he says,'Lead me from death to immortality,' there is nothing there, as it were, hidden (obscure, requiring explanation).