The conclusion is at the end. You could write a book on this alone.
One improbable possibility is Ἦν … ἐρχόμενον forms a periphrastic, but as A. T. Robertson explains, position makes this unlikely.
There was (ἠν [ēn]). Imperfect indicative. Emphatic position at the beginning of the sentence and so probably not periphrastic conjugation with ἐρχομενον [erchomenon] (coming) near the end, though that is possible. --
Robertson, A. T. (1933). Word Pictures in the New Testament (Jn 1:9). Nashville, TN: Broadman Press.
Robertson agreed about the pre-existent light.
This true light had been on hand all the time in the darkness (ἠν [ēn] imperfect, linear action) before John came. --
Robertson, A. T. (1933). Word Pictures in the New Testament (Jn 1:9). Nashville, TN: Broadman Press.
Robertson presented a debate about what φωτιζει παντα ἀνθρωπον means:
Lighteth every man (φωτιζει παντα ἀνθρωπον [phōtizei panta anthrōpon]). Old verb (from φως [phōs]) to give light as in Rev. 22:5 and Luke 11:35f. The Quakers appeal to this phrase for their belief that to every man there is given an inner light that is a sufficient guide, the Quaker’s text it is called. But it may only mean that all the real light that men receive comes from Christ, not necessarily that each one receives a special revelation. --
Robertson, A. T. (1933). Word Pictures in the New Testament (Jn 1:9). Nashville, TN: Broadman Press.
J. P. Lange discusses this all the way back to the church fathers. He mention s that πάντα ἄνθρωπον eliminates the possibility that Ἦν refers to only before John and means before every human.
The essence of this universal advent is to be recognized in the fact, that the Logos shines in every man in his religious and moral nature and experience, as the λόγος σπερματικός. That the expression “every man” needed not the addition: that cometh into the world, is evident. And the phrase: “to come into the world,” is not used of the natural birth of an ordinary man, but is reserved for Christ. --
Lange, J. P., & Schaff, P. (2008). A commentary on the Holy Scriptures: John (p. 66). Bellingham, WA: Logos Bible Software.
Lange goes on:
[Which lighteth (enlightens, illuminates) every man—ὃ φωτίζει πάντα ἄνθρωπον.—There is much force in the singular. Quisquis illuminatur, ab hac luce illuminatur (Bengel). Different interpretations: 1. The light of reason and intelligence (Cyril of Alex.). Better: Both the intellectual and moral light (reason and conscience) given to all men, as distinct from the spiritual light of saving grace given to believers. The former is the basis of the latter. 2. The inward spiritual light given to all (Quakers). 3. The light of grace given to believers only, or to every one to whom Christ was preached (Crosby). 4. Intellectual and spiritual light sufficient for the salvation of Jews and Gentiles, though the majority are so blinded by sin as not to see Him. “Christ enlightens all as far as in Him lies” (Chrysostom, Hom. 8). Christ gives sufficient light to every man to leave him without excuse, but not sufficient to save (Arrowsmith, Ryle).—Comp. 3:19: “light is come into the world;” 12:46: “I am come a light into the world;” 6:14: “that prophet that should come into the world;” 18:37.—P. S.] --
Lange, J. P., & Schaff, P. (2008). A commentary on the Holy Scriptures: John (p. 66). Bellingham, WA: Logos Bible Software.
Ἀληθινός is a favorite term with Plato and John to signify that which is genuine, archetypal, original, true to the idea. It occurs eight times in the Gospel, ten times in the Apocalypse, three times in the first Epistle of John, but elsewhere only five times in the N. T. In this passage it stands in contrast not so much to the cosmical light (Dr. Lange), as to the borrowed intellectual and moral light of the Baptist and other human teachers; comp. 5:35; Matth. 5:14, where believers generally as members of Christ are called the light of the world. It is lumen illuminans, as distinct from the lumen illuminatum.—P. S.] --
Lange, J. P., & Schaff, P. (2008). A commentary on the Holy Scriptures: John (p. 66). Bellingham, WA: Logos Bible Software.
William Barclay’s translation took an unlikely remote connection with the relative pronoun, but he does make a good statement out ἀληθινόν.
John 1:9
He was the real light, who, in his coming into the world, gives light to every man.
IN this verse, John uses a very significant word to describe Jesus. He says that Jesus was the real light. In Greek, there are two words which are very like each other. The Authorized Version and the Revised Standard use the word true to translate both of them; but they have different shades of meaning. The first is alēthēs. Alēthēs means true as opposed to false; it is the word that would be used of a statement which is true. The other word is alēthinos. Alēthinos means real or genuine as opposed to unreal. --
Barclay, W. (2001). The Gospel of John (Rev. and updated., Vol. 1, p. 63). Edinburgh: Saint Andrew Press.
Some things written in scripture:
All things were made [became] through him, and without him was not any thing made
(John 1:3, ESV)
For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who by their unrighteousness suppress the truth. 19 For what can be known about God is plain to them, because God has shown it to them. 20 For his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse. 21 For although they knew God, they did not honor him as God or give thanks to him, but they became futile in their thinking, and their foolish hearts were darkened. 22 Claiming to be wise, they became fools, 23 and exchanged the glory of the immortal God for images resembling mortal man and birds and animals and creeping things. (Rom. 1:18–23, ESV)
For when Gentiles, who do not have the law, by nature do what the law requires, they are a law to themselves, even though they do not have the law. 15 They show that the work of the law is written on their hearts, while their conscience also bears witness, and their conflicting thoughts accuse or even excuse them (Rom. 2:14–15, ESV).
Thus, Paul essentially wrote that every person has the real light. As a person who grew up in church understanding what Paul wrote in Romans 1 and 2 about the non-Jews is difficult. It is when you look at how secular people struggle with this that one understands. Here is one example of many.
https://biologos.org/articles/does-evolutionary-psychology-explain-why-we-believe-in-god
And here is even a clearer example:
Such an overwhelming fear of a vindictive, disappointed God certainly wasn’t something that my parents had ever taught me.
https://blogs.scientificamerican.com/bering-in-mind/god-may-work-in-mysterious-ways-but-cognitive-science-is-getting-a-handle-on-them/
Just as John 1:3 did not preclude the rest of the Trinity's involvement in creation, 1:9 did not preclude the rest of the Trinity. The appearance of God in human form would be Jesus because the rest of the Trinity doesn't have human form. John 8:56, though not clearly stated, is our best statement of this in the Bible.