She told the court the helicopter crew flew towards the direction the laser came from and it was pointed at them again, with each strike lasting about five seconds.
They saw a group of people sitting on the back deck of a house on Asquith Ave and arranged for a police car to visit the address.
Police asked the group who had shone the laser and, Ms Prasad said, Spiers admitted it was him, saying he thought it would be a fun thing to do.
She said O'Hare-Knight admitted owning the laser and said he didn't realise it was such an offence to shine it at a helicopter.
In a brief opening address, Spiers' lawyer Scott Leith said his client had never made such an admission.
"In the loud environment of an 18th birthday party some wires got crossed, the police made some assumptions and Mr Spiers, who was only 17 at the time, was arrested.''
O'Hare-Knight's lawyer Rosemary Thomson said her client admitted to owning the laser, but he never pointed it at the aircraft.
"He took it to the party. He did not, however, point it at any time in the direction of the helicopter and he did not therefore cause unnecessary danger to an aircraft, somebody else did.''
Sergeant Al Grant, who was one of the crew onboard the helicopter, told the court the laser had impaired his vision.
"For a few seconds it filled the cockpit of the aircraft with a strong green light.''
He said any bright lights in the aircraft at night were strictly against the rules.
"It would be a horrendous breach of safety protocol to turn on, say, a torch, or to have a camera flash go off.''
The trial, before Judge Nevin Dawson, is set down for four days.
