Short answer: From a traditional evangelical perspective, the most likely human author of the Gospel passage containing John 8:12 is John the Apostle — the “disciple whom Jesus loved” — writing the Gospel of John as an eyewitness testimony about Jesus.

Key points an evangelical would emphasize

– Identity and background
– John was one of the twelve apostles, son of Zebedee and brother of James, a fisherman called by Jesus (Matt. 4:21–22; Mark 1:19–20).
– He belonged to Jesus’ inner circle (with Peter and James) and is often identified in the Fourth Gospel as the “disciple whom Jesus loved” (e.g., John 13:23; 19:26; 21:7,20), which evangelicals take as indicative of an eyewitness source.

– Early church testimony
– Fathers of the early church (e.g., Papias, Irenaeus, Clement of Alexandria) attribute the Fourth Gospel to John the Apostle. Evangelicals regard this consistent early testimony as strong evidence for Johannine authorship.

– Internal and literary evidence
– The Gospel itself contains many details that suggest an eyewitness perspective (specific locations, personal encounters with Peter and the beloved disciple).
– The style, vocabulary, and theological emphases of John correspond with 1, 2, and 3 John, supporting common authorship.
– John 8:12 (“I am the light of the world…”) fits the Gospel’s major motifs (light vs. darkness, “I am” sayings, signs pointing to Jesus’ identity).

– Date and place
– Many evangelical scholars date the Gospel to the late first century (commonly c. AD 85–95) and place its composition in Ephesus or the surrounding region of Asia Minor, where John is traditionally said to have ministered in his later years.

– Theological significance (evangelical emphasis)
– Evangelicals affirm that John wrote not only as an eyewitness but under divine inspiration (2 Tim. 3:16), so his Gospel is a theologically reliable and authoritative witness to the person and work of Christ.
– John’s presentation of Jesus as the incarnate Word and the “light of the world” (John 8:12) is central to evangelical preaching and doctrine about Christ’s unique revelation and saving work.

– Acknowledgement of alternative critical views
– Some critical scholars propose a Johannine community or a later redactor rather than the apostle himself. Evangelicals typically consider those theories but generally maintain apostolic (or apostolic-circle) authorship based on the weight of early testimony, internal claims, and the Gospel’s theological coherence.

If you’d like, I can:
– Summarize the historical evidence more fully (Papias, Irenaeus, manuscript evidence),
– Compare evangelical views with critical scholarship in more detail,
– Or explain how John 8:12 fits into the Gospel’s theology and pastoral use.