Every year the Phoenix Zoo does a "Zoolights" fundraiser from about Thanksgiving until the end of New Year's week. The display changes each year and seems to attract bigger crowds each year. Perhaps going the day after Christmas was part of the reason for the massive crowds this year.
The big blue tree uses 30,000 lights which raised the question for how long it takes to set up for Zoolights. Research indicates it takes a crew of four 12 weeks to install the lights.
In addition to lighting the trees, there are a lot of animals shapes, many which appear to move. The monkey "swings" across a wire above the restrooms while birds "fly" in the trees nearby.
This year they added a light show in the lake with the trees, 12' floating tubes, and a 24' sphere changing colors and other effects in time to the music. I forgot the camera so all the photos are from my phone.
The Phoenix Zoo is a private non-profit operation that doesn't recieve any public funding. Zoolights is their largest fund raiser of the year and worth a visit if you're in town.