They're Christmas lights, dude. Jews don't string up lights. So while it's properly a "holiday party" at your office, and you wish people "happy holidays" (not knowing their religion), you just don't put up holiday lights. No such thing.
I was going to just let this go, but I decided I'd comment on it.
The celebration of Christmas as a Christian holiday is as an overlay over existing celebration that occured on December 25th. The Egyptians celebrated the birthday of Ra, the sun god, on that day, as it was just after the winter solstice. Many other societies have also had celebrations on the solstice, and December 25th only became a christian holiday by the declaration of pope Julias I in the 4th century.
So, as somebody who isn't religious, I'm going to stick with the term "Holiday lights". I think there's a good reason to celebrate the days getting longer (*beyond* the fact that it's the start of the good skiing, which is a reason of its own) even if you don't believe there's a deity involved.
I may switch to "Solstice lights", but I think that could be more bother than it's worth.