Have I not seen Jesus Christ our Lord?
-- I Corinthians 9:1
And last of all he was seen of me also, as of one born out of due time.
-- I Corinthians 15:8
The salient points in the three accounts of Paul's conversion in Acts are that he could not see who was talking to him because he was blinded by the light, and that he did not recognize who it was that was speaking to him:
And as he journeyed, he came near Damascus: and suddenly there shined round about him a light from heaven: ... Who art thou, Lord? ... And Saul arose from the earth; and when his eyes were opened, he saw no man: but they led him by the hand, and brought him into Damascus. And he was three days without sight, and neither did eat nor drink.
-- Acts 9:3, 5, 8f.
And it came to pass, that, as I made my journey, and was come nigh unto Damascus about noon, suddenly there shone from heaven a great light round about me. ... Who art thou, Lord? ... And when I could not see for the glory of that light, being led by the hand of them that were with me, I came into Damascus.
-- Acts 22:6, 8, 11
At midday, O king, I saw in the way a light from heaven, above the brightness of the sun, shining round about me and them which journeyed with me. ... Who art thou, Lord?
-- Acts 26:13, 15.
Nevertheless he calls it "seeing" the Lord.
Meanwhile the witnesses in Acts 9 heard only a voice, and saw no one.
In Acts 22 the witnesses saw only the light, and heard nothing.
In Acts 26 Luke has Paul say that he and the witnesses were knocked to the ground after being enveloped by the light.
Most notably there, Luke has Paul summarize the whole experience explicitly as a heavenly vision, which is the experience through which Paul says elsewhere that he received his gospel (II Corinthians 12:1, 7; Galatians 1:12, 16; 2:2; Romans 16:25; Ephesians 3:3, 5), whereupon the governor Festus pronounced Paul a madman.
No one "saw" the Lord in the Acts accounts, but in the final analysis Paul's claims to have seen the Lord are unfalsifiable because they are heavenly and beyond our ken. They are as a result self-insulating and self-authenticating.
