A bus driver with 35 years' experience thought a motorbike rider had already passed him when he turned into a road and killed him.
Clive Randall, 58, saw Paul Lyall coming in the opposite direction along Furzehill Road, Borehamwood.
But, St Albans crown court heard today that he told the police he was looking up the road for cars when he struck 42-year-old Mr Lyall in a momentary lapse of judgement.
Prosecutor Alex Krikler said Mr Lyall, a married father-of-two, was riding a silver Yamaha 125cc motorcycle at 10.30pm on March 28 last year.
Mr Randall was driving a Metroline double decker on route 107 along Furzehill Road. He was travelling at 17 miles per hour in the 30mph zone when he turned right into Ashley Drive and hit Mr Lyall, who was travelling in the opposite direction along Furzehill Road.
Mr Lyall, who had been a decorator, had his head light on and was not exceeding the speed limit.
Members of the public and the bus driver went to his aid. An ambulance crew and an accident and emergency consultant arrived, but he was pronounced dead at the scene from major traumatic injuries.
The bus driver told the police: "I was just turning then all of a sudden there was a bang on the windscreen. I thought he had passed."
In a victim impact statement, Mr Lyall's wife said she and their two children had been devastated by his death. Her son was scared of getting on a bus to go to school because that was the kind of vehicle that had killed his father.
She described her husband as a "funny, loving, caring and proud man."
Randall, of Vale Avenue, Borehamwood, pleaded guilty to causing death by careless driving. He had no previous convictions.
Matthew Gower, defending, said: "Mr Randall wants to pass on his utter regret and sympathy to Mrs Lyall and her family."
He said the football referee, who volunteers with the Sea Scouts, had led a blameless life. He has lost his driving job and now works for John Lewis.
Since the accident, his wife had described him as being a "recluse and a zombie" and he had been referred for psychiatric help.
Judge Andrew Bright said: "It is a tragedy of the highest order. Paul Lyall was in his early 40s with a devoted wife and was a father of two young children."
He told the bus driver: "You made a dreadful error of judgement that cost Mr Lyall his life."
But Judge Bright said there was no point in locking Randall up for a few weeks and passed a two-year community order with 200 hours' unpaid work. He must pay £500 costs and is banned from driving for two years.