I sort of notice this contradiction every time I read the Book of Acts. Hopefully the discussion of what seems to be a contradiction will never cause someone to stumble and often they can be used as a teaching opportunity to more solidly ground believers on stronger foundations.
It is interesting that the account of the events of the Saul / Paul conversion experience differ slightly between the account at the beginning of Acts and much further through.
Acts 9 Authorized (King James) Version (AKJV)
3 And as he journeyed, he came near Damascus: and suddenly there shined round about him a light from heaven: 4 and he fell to the earth, and heard a voice saying unto him, Saul, Saul, why persecutest thou me? 5 And he said, Who art thou, Lord? And the Lord said, I am Jesus whom thou persecutest: it is hard for thee to kick against the pricks. 6 And he trembling and astonished said, Lord, what wilt thou have me to do? And the Lord said unto him, Arise, and go into the city, and it shall be told thee what thou must do. 7 And the men which journeyed with him stood speechless, hearing a voice, but seeing no man. 8 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. 9 And he was three days without sight, and neither did eat nor drink.
Acts 22 Authorized (King James) Version (AKJV)
6 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. 7 And I fell unto the ground, and heard a voice saying unto me, Saul, Saul, why persecutest thou me? 8 And I answered, Who art thou, Lord? And he said unto me, I am Jesus of Nazareth, whom thou persecutest. 9 And they that were with me saw indeed the light, and were afraid; but they heard not the voice of him that spake to me. 10 And I said, What shall I do, Lord? And the Lord said unto me, Arise, and go into Damascus; and there it shall be told thee of all things which are appointed for thee to do.
Apologies if this has ever been covered in the past and I've simply forgotten about it. Even if that is the case covering it again might be useful for someone who hasn't seen it before and the discussion may be useful if a non-believer has ever heard of it and tries to use it as an argument point when someone is preaching the gospel message.