Verse 67

तमस्ता तमसो दीपासत्तायां स्फुटतां गता ।दीपसंबन्धसमये सा चोत्पद्य विनश्यति

In plain words

The very darkness of darkness becomes distinct only where a lamp is absent; the instant a lamp appears, that darkness, having only just arisen, perishes.