The lights can be dimmed by adjusting the brightness setting on the light controller. Most light controllers have a brightness setting that can be adjusted either by a knob or a button. Some controllers may have a dimmer feature that allows you to adjust the brightness of the lights. If you don't have a controller, you can also dim the lights by using a dimmer switch. A dimmer switch is a device that can be attached to the light string and allows you to adjust the brightness of the lights.