I ask this question based on the below points and below verses.
- Acts 9:1 says that Saul saw a bright light from heaven and Saul became blind(at least temporarily)
- Others did not see anything by just heard the sounds and their sight was not impacted
- When Barnabas takes Saul to the Disciples in Jerusalem Barnabas tells them that Saul saw Jesus.
- I believe there are verses in Paul's letters where he talks about his experience with Jesus
- This event is mysterious as if there was a bright light every one should see it and cannot be localized to one person in a group. On the other hand, sound can be a whisper in one person's ears that others around don't hear.
Acts 9:3 As he neared Damascus on his journey, suddenly a light from heaven flashed around him. 4 He fell to the ground and heard a voice say to him, “Saul, Saul, why do you persecute me?”
Acts 9:7 The men traveling with Saul stood there speechless; they heard the sound but did not see anyone.
Acts 9:27 But Barnabas took him and brought him to the apostles. He told them how Saul on his journey had seen the Lord and that the Lord had spoken to him, and how in Damascus he had preached fearlessly in the name of Jesus.