Ah, washing a Christmas sweater with lights requires a bit of extra care. The first step is to unplug the lights and remove any batteries. Then, you'll want to hand wash the sweater in a gentle detergent to avoid damaging the lights or the fabric. Be sure to gently scrub the fabric and avoid putting too much pressure on the lights. After washing, you can let the sweater air dry or use a low heat setting on your dryer.