The easiest way to dim LED Christmas lights is to use a dimmer switch. Most dimmer switches are compatible with standard LED bulbs, but it's best to check the manufacturer's specifications before purchasing. If you don't want to use a dimmer switch, you can also use a dimmable LED strip controller or dimmable LED bulbs with a dimmable lamp. Just make sure the dimmer you use is compatible with your bulbs and lamps. Alternatively, you can try using a dimmable LED driver, which is a device that allows you to adjust the brightness of the lights.