God is the light. Darkness is an impersonal force, the rejection of God. The devil is in the darkness, but is not the darkness, and his power is dependent on men believing a lie. However, the power of darkness is not like the power of light. Light is a person, God himself.
Darkness is impersonal, the rejection of the light.
Because the premise of his kingdom is that every member of it may be his own god, satan has no true subordinates. More contrasts between light and darkness. Light possesses its own real power, darkness only illusory power. Light is living, darkness is dead. Light overcomes darkness.