7 Answers

It all depends on the context that you ask the question.

Radiant energy

light is energy. The higher the vibration of the light, the less visible it is to the naked eye. This is why seeing auras requires a spiritual awareness, but you still rely on your eyes to see them.

Depends upon upon the level of consciousness one is refering to.  Subjectively: Ignorance is the presences of darkness; Knowledge is the Light of ignorance; Understandsing the Light of knowledge; Wisdom the Light of understanding; Truth the light of wisdom and finally Love thr light of truth.   Understanding is the Light of heart and mind, which ever leads into the Spiritual Heights .  Whereas Objectively:  the Light of the Sun can burn the skin and eyes, yet nutures all Earthly Life, by pushing back the darkness of the night. 

Jesus is the light, the truth and the way.

Roger get a life. Feathers are light relatively speaking.

It's the absence of dark.
In the Bible God said. "Let there be Light." and there was. At that very exact same instance the Big Bang occured. So there is a God of the Universe. My all time favorite story is called: "The Last Question." It's in a book of short stories by Asimov. Called "The Nine Tomorrows." It'll blow your mind.