The biggest thing you can do is to switch to LED lights. If you do, you’ll use up to 70 percent less energy than you would with traditional incandescent bulbs. Plus, you won’t need to replace lights as often. LEDs last about 10 times longer.

“If you want the lights, try to get the most efficient ones,” said Shahzeen Attari, an associate professor at Indiana University Bloomington who studies environmental psychology. “And when you’re not using them, turn them off.”

Eleanor Stokes, a research scientist at the University of Maryland who has worked with NASA to gather satellite data on our lighting habits, agreed. “I’m all about being festive,” she said, “but you don’t need to be festive at, like, 3 a.m.” Putting your lights on a timer can have a “huge benefit,” she said.

The Energy Department recommends leaving them on for up to eight hours a day, from dusk to around midnight. Not only will this conserve energy, but it’s better for wildlife. Heavy light pollution can be deadly for some animals by disrupting the daily cycle of light and dark.

Another tip: You can use an extension cord in places where you want to connect strings but don’t really need lights.