He offered to inject one buyer with the drug, saying he'd studied nursing and knew how to do it safely.
Lumsden, originally from Northland, "accepts without reservation" the significant impact his actions had on his victims, defence counsel Elizabeth Bulger said.
Victim impact statements were compelling, Bulger said, with one man in particular talking about the depth of anguish he has suffered.
Lumsden now believes he is in a position to give back to the community, Bulger said.
He has written a "heartfelt" letter to an Auckland body positive organisation, which provides services for young men like him.
Bulger said his diagnosis of HIV was a turning point in his life, where "things started going downhill from there".
It highlighted the lack of community support for people in his situation, Bulger said.
She pushed for a sentence of home detention, but Judge David Saunders concluded that a sentence of imprisonment was necessary for actions that were "quite reckless".