The Aurora Borealis is often only seen north of Iceland, but occasionally comes further south.
Inishowen and Fanad peninsulas in north Donegal have had glimpses of the lights in the past few years, but nothing like the display yesterday, which was so good the lights were visible further south in counties Tyrone, Leitrim and Sligo.
And with Met Eireann predicting clear skies after midnight tonight and again on Sunday night, more huge crowds are expected.
"We've been inundated with bookings," said Rina Douglas, manager of the Malin Hotel.
"I went out to watch the lights myself and it was the most incredible sight," she said.
Families from Dublin, Kilkenny and Clare made inquiries yesterday, all taking advantage of special Northern Lights rates.
"We're doing two nights' bed and breakfast with one evening meal for €150 – and the lights are free," said Rina.
Jennifer O'Donnell, from Visit Inishowen, said the display in the early hours of yesterday was a "jaw-dropping" experience.
"It was incredible," she said.
"We just happen to be in the best place in Ireland to see them. There is very little light pollution and an increase in this solar activity this year."
Aurora Borealis means 'dawn of the north'. Scientists at The Northern Lights centre in Canada now believe the intensity of the displays comes in cycles. This week's displays may not be repeated in Ireland for another 11 years.
The lights of the Aurora generally extend from 80km to as high as 640km above the Earth's surface.
Inishowen Tourism has a list of the best places to see the Northern Lights on www.visitinishowen.com