A room that is absent of darkness?
Or a person who is humble?
If you’re speaking as a metaphor, then I guess you can make an abstract description of “full of light”. However, “full of light” can be used to refer to light itself. Although, if you use “full of light” to refer to light, it would just be recursive, and plainly not true, IMO. Or maybe you can say the universe is “full of light.” Sun/Stars radiate light, therefore, you could say “full of light” as an expression.
Or did I miss the point?
A light bulb that is switched on.
Then when JEsus said," You will become full of light"
means nothing, it is an expression? of what?
OR it means a person is turn on? 
what is full of light?
The police man’s flashlight is full of light, blindingly bright.
No.
Light illuminates a darkened room. Ignorance and superstition exist in darkness, we must pull them out in the light so we can expose them to scrutiny and investigation.
You can be a light to the world, well, that’s too ambitious, maybe to your family and friends and coworkers. Then to the world.
There are a lot of individuals that are shining lights. No, not the Hollywood whose stars are dimmed, but the scientists and inventors, Buddha, Mother Theresa, Ahknaton, a compassionate doctor, etc. But as to full of light, I only know of one.
He was of divine birth. His name was Jesus, the Christ.
IMO, his teachings are the greatest, better than Buddha’s, better than the
Taoist, Mohammed’s, etc. Jesus was the greatest.
John 14:6. Jesus answered, “I am the way, the truth and the life.”
But not everyone is ready or worthy to receive the truth.
So Jesus spoke in parables and allegories.
To the uninitiated, he spoke about ordinary things. The initiated understood him. To his inner circle, he demonstrated laws and principles of everything: health, the sciences, the human body, etc and instructed them to spread the work. He told them they can do greater things than him. We have here on earth right now that can do greater things.
When he told his disciples to spread the work, they also healed the sick. Too bad, Christian churches of today devote their time to preaching and not healing, theory not practice.