Light has both physical and philosophical aspects. And we have no reason from the language of Genesis 1 to demand that this light was EITHER one OR the other. Every hermeneutic I know of would insist on interpreting this as BOTH physical AND philosophical light. In fact, I suggest that the light created here was nothing less that the very knowledge, word, power and righteousness of God shining forth as His word was uttered.
And this light that was spoken was not created, per se, but a sudden revelation or translation of the knowledge, goodness, power, love and righteousness of very God into the physical medium we call light.
If there ever actually was anything like a "big bang", this was it, when all the matter and energy of the universe was created instantaneously from and through the word of God. It is why the Apostle John says,
In the beginning was the Word, and the Word was with God, and the Word was God. He was in the beginning with God. All things were made through Him, and without Him nothing was made that was made. In Him was life, and the life was the light of men. And the light shines in the darkness, and the darkness did not comprehend it. [John 1:1-5]
He equates God's word with God and personifies the Word with the pronoun "him", because God's Word is fullest the expression of Himself.
The Psalmists give the same interpretation of the light as God's word:
The entrance of Your words gives light. Psalm 119:130
By the word of the Lord the heavens were made, And all the host of them by the breath of His mouth. Psalm 33:6
God's creative power is His Word, and that Word is the very expression of Himself made intelligible to the mind of man. The light is God's medium to convey his knowledge to his creation, particularly to man.
So, turning to your three questions:
- If literal: Does this include both non-visible & visible light found on the Electromagnetic-Spectrum (Radio to Gamma) / Wave & Particle?
Yes. What we define as "light" is that effect which the sun and stars were created to generate on the fourth day of Creation. The sources of light were created by God, and the light itself is the product of His word, whether by the direct speaking of God or the objects he created to perpetuate that light. I would argue that the light produced by the Sun and stars is less in effect and power than the light that shone on the first three days. But it is also the work of God's word.
- If figurative: What is the light symbolizing?
If the light is symbolic of anything, it symbolizes God's Word. To Christians it is a symbol of the Messiah, who said, "I am the light of the world" [John 8:12 and 9:5]. But even more than figurative, it is rich with philosophical meaning, as an expression of God's power, love and desire to fill the world with life. Light is often used as a symbol for knowledge. But that would imply that light is something less than knowledge (of which it is a mere symbol). This light is not only a symbol of knowledge, but the medium of all knowledge: we would have no knowledge without the light, as there would be no medium to convey knowledge to our eyes and our mind. The Greek philosophers, Hellenistic Jewish and early Christian philosophers worked this out long ago.
- If both: What is the complete light?
The "complete light" is that "true light that gives light to every man", which has come into the world in the person of Jesus [John 1:9]. Jesus said of himself "As long as I am in the world, I am the light of the world". He also said to his disciples, "you are the light of the world" [Matthew 5:14]. Moses' face shone after he had been in the presence of God. This light reflected from God in his face was not Moses' own light, but God's light in him. Likewise, Jesus' face shone like the sun on the mount [Matthew 17:1-2]. He is the One who God sent, who was like Moses, bringing God's word and covenant to God's people.
The Lord your God will raise up for you a Prophet like me from your midst, from your brethren. Him you shall hear... Deuteronomy 18:15
The darkness did not "comprehend" this light, but neither has it in any way "overcome" the light. ("Comprehend" and "overcome" are two of the most common translations given of the Greek word katelaben in John 1:5.)