However, ERA member Tania Tetitaha ruled in her report that all allegations did not constitute bullying or unreasonable behaviour.
But the ERA did uphold a personal grievance submitted by Rampton.
The incident involved Wilson using a phone to reflect sunlight into Rampton's eyes during an office quiz in December 2017.
Due to Rampton's head injury, she suffered from photo sensitivity, and suffered pain and discomfort due to Wilson's actions.
She later became unwell, and attended the Emergency Department at Wellington Hospital.
Three days later she reported the incident both internally and to police.
Both a doctor's report and physiotherapist assessment found the incident had aggravated her concussion symptoms, including headaches and disorientation.
An internal investigation was conducted, and found the incident was "entirely accidental".
"There is no evidence of any deliberate or malicious intention by Donna to cause Angela harm, and in particular, from the three eyewitness accounts, there was no deliberately planned playing of light on to Angela," the internal review concluded.
However, Rampton later raised a specific personal grievance about the conduct leading to the incident, the impartiality of the decision-maker, investigation process and conclusions.
The ERA found the Council had declined to investigate the incident further and took no further action.
"This inaction cannot be justified in terms of the requirements of the Employment Relations Act 2000," ERA member Tania Tetitaha said.
Tetitaha ruled that there was merit to Rampton's concerns about the incident and the subsequent investigation.
"There were issues about the decision-maker's impartiality, adequacy of investigation and conclusions.
"Under examination Jenni Rains [the investigator] admitted she did not see the incident. This was not stated in the report. Instead the report stated Rains 'had not observed there to be any deliberate targeting of Angela in the light-reflection incident'.
"This inferred she saw the incident when she did not. "
The ERA report stated that Wilson has been deliberately shining the light around the room, and shone it in the direction of Rampton's face - despite knowing she suffered from photo sensitivity.
"I do not find Wilson consciously intended harm. This was however reckless. It was unreasonable behaviour.
"This was a one-off incident that caused unintended harm," Tetitaha said.
"However, the Council's inaction regarding Rampton's personal grievance caused disadvantage in her employment."
Tetitaha ruled that in terms of compensation, Rampton had suffered physical and emotional harm as a result of the incident.
"The incident was preventable. There was physical and emotional harm caused. There is an ongoing failure to investigate the personal grievance.
"Deterrence of this behaviour is required. In my view $20,000 is an appropriate award," Tetitaha said.
Wellington City Council was ordered to pay this sum to Rampton within 28 days.
