Strobist has some tips for photographing Christmas lights. They begin with this advice:
The problem with 98% of the photos of Christmas lights is that most people wait until way too late to start shooting. After it gets completely dark, you can either have the lights or the surroundings properly exposed. But not both.
Conversely, if you were to shoot the lights in the middle of the day, they would not show up at all. The trick is find the sweet spot (actually there is a whole range of sweet spots) where the ambient light and the Christmas lights balance.