Sun glare may have affected the vision of two drivers accused of causing the death of a cyclist near Aberystwyth, a court heard.
Paul James, 61, a county councillor, died on the A487 in April last year.
Lowri Powell, 44, from Penrhyncoch and Christopher Jones, 40, from Devil's Bridge, deny causing death by careless driving at Swansea Crown Court.
Both defendants told police they had not seen Mr James because they had been dazzled by the low sun.
The court heard Ms Powell clipped Mr James with her Ford Galaxy car, knocking him off his bike, while Mr Jones' Vauxhall Vectra ran over him, dragging him down the road.
Professor Graham Edgar, an expert in cognitive psychology and situation awareness, said glare could affect a driver's ability to recognise hazards before reacting to them.
He said people could see things but still not be fully aware of them, and sun glare had a significant effect.
"It tends to drop the contrast of everything in the world, making everything harder to see," he said, comparing it to looking through lace or a net curtain.
Prof Edgar said it could affect a driver's ability to differentiate between grass and rocks on the roadside.
However, he said the motorists would have seen Mr James' high-visibility jacket.
Collision investigator Victoria Eyers told the court Covid-19 lockdown restrictions meant she had not been able to visit the scene in Ceredigion.
But she told jurors glare from the sun and dark roadside foliage in the shadows would have made Mr James difficult to see, even in his high-visibility jacket.
During her investigation, she calculated Mr James would only have become visible to Ms Powell from a distance of 13 metres away.
"To be able to react and brake to a stop, she would need to be travelling at 15mph or less," she said.
To see him and swerve, she estimated Ms Powell would have needed to have been driving at around 9mph, and she was travelling at 52mph.
The trial continues.