But since we quoted the language of Paul regarding Christ, where He says of Him that He is “the brightness of the glory of God, and the express figure of His person,” let us see what idea we are to form of this. According to John, “God is light.” The only-begotten Son, therefore, is the glory of this light, proceeding inseparably from (God) Himself, as brightness does from light, and illuminating the whole of creation.(Book I, Chapter 2, Part 7)

Brightness is an innate characteristic of light. It is an aspect of the light which can be seen.

It is much more difficult to perceive other properties of light: the particles and waves of radiation, photons, the electromagnetic spectrum...

Light can be described as having five characteristics: intensity, propagation direction, frequency, polarization, and phase.

God can be described as having three fundamental aspects: Father, Son, and Spirit. The Son proceedeth from the Father as intensity characterises light.

The Son is very intense.