Half a kilometre of fairy lights, 15 decorated trees, arches and lasers now adorn the children's ward thanks to Williamson.
The end result was "just gorgeous" and had lifted the spirits of patients, their whanau and staff, paediatric nurse clinical leader Di O'Conner said.
And it wasn't just the children enjoying the lights.
"The nurses have all had their photo taken with the reindeer and had a lot of fun," O'Conner said.
Pani Martin, whose daughter Aaliyah was a regular inpatient due to a chronic lung condition, said the decorations had been a welcome distraction.
"We come in every three months for two weeks so here is like a second home to us."
Aaliyah, who helped decorate the ward, said it was a "fun" experience.
It was not just the children's ward Williams was lighting up. His Napier home was a well known attraction in The Bay each Christmas.
"We get 10,000 to 20,000 people past each year. I did up my neighbours' house too this year."
He loved Christmas and had seven decorated trees this year, he said.
"I like to go over the top, way over the top."
He did it because it brings people so much joy, he said.
"Everyone who sees the lights, they're smiling, everyone is just happy."
- RNZ
