You can tell the holidays are approaching when customers call with this question: Will holiday lights make my bill go up? The answer is yes. Or no. Or maybe so. It depends on how many lights you're using, and for how long. Just for fun, here's a sample calculation:
So a few lights won't have a big impact. But a big-impact lighting display may nudge your costs up a bit.
Note that LEDs are more expensive to purchase but cheaper to operate. They also last longer and are cool to the touch. As more and more people switch to LEDs, the energy savings add up.