Anita Fogarty contacted the Otago Daily Times last week, frustrated at being unable to explain the recurring lights near the summit of Flagstaff, above Dunedin's central city.
She had watched from her Opoho home as the lights returned night after night for more than a year, sometimes several times a week and often about 8.30pm.
They changed colour and moved around near the summit at rapid speeds, sometimes for up to an hour at a time, other times disappearing only to return later, and all without making a sound.
Ms Fogarty, an administrator at the Dunedin School of Medicine, said she had ruled out helicopters and other passing aircraft, and doubted spotlighting hunters could be the cause because of the moving lights' rapid speeds.
She also walked regularly in the Flagstaff area and, while an explanation had eluded her, she insisted she was "not nutty, believe me".
"The lights come in and go away again. Sometimes they are green and red as they move along.
"What are UFOs? They are lights that I can't explain."
However, it appears the seemingly unearthly source of the lights might be closer to home after all, with mountain bikers on night rides the suspected source.
The Mountain Biking Otago website advertised tracks in the Flagstaff and Swampy Summit area, as well as regular night rides beginning at 7pm from the end of daylight saving.
Another online mountain biking website had been used by Dunedin riders to organise regular Wednesday night rides, from April to October.
Ms Fogarty's last sighting was this week, on Wednesday night.
Mountain Biking Otago president Hamish Seaton said when contacted Ms Fogarty's sightings would "definitely be mountain bikers".
There were several informal groups that regularly took to the city's trails, including the Flagstaff area, on winter nights.
The earlier onset of darkness meant those wanting an after-work ride needed to do so at night, and headlamps had now become much cheaper and more powerful, he said.
Bike Otago owner Greg Leov said groups of up to 20 riders would head out wearing headlamps and on bikes with red tail-lights, and were venturing into new terrain.
"They are even riding Signal Hill, so people from Roslyn round to Maori Hill are now seeing lights going down Signal Hill, and they've never seen that before."
Flagstaff's height meant the riders were particularly visible to some people, and changing terrain meant lights would appear to flicker and change colour as riders' angles did, he said.
Ms Fogarty said the explanation was good news.
"I hope it is that, because it was starting to unnerve me a bit."
