The answer to this question depends on the type of Christmas lights. Some energy-efficient LED Christmas lights are designed to run on lower voltage, including 12 volts.
However, most LED and virtually all traditional incandescent Christmas lights typically require a standard 120-volt line.
If you plan on using Christmas lights in a 12-volt system, check the packaging or specifications of the lights to ensure they are compatible. Using lights that require a higher voltage of 12 volts could damage them, cause them to be less bright, or even pose a safety hazard.
We do carry a line of 12-volt light strings manufactured with accessory plugs. They run on a DC current and can be plugged into any accessory outlet. This makes them easy to use in cars, RVs, and golf carts. We love them for the Holidays - think parades and lighting wreaths on car grills. We also enjoy them all year "plugged" into marine batteries using accessory socket to clips adapters.
Customers have successfully used 12 DC lights when the ends are clipped in AC applications. Remember that since our strings are tailored to be used with a DC source, they will flicker. If the lights are stationary, that's not so noticeable but when they move, it's more visible to the eye. (They only flicker when connected to a 12-volt AC source. Under regular operation, they are purely steady with no electricity-related variation in appearance. Installing a filter on the input line can mitigate the waveform variation when used in AC systems.)