A standard string of incandescent Christmas lights uses 40 watts of electricity. LED lights are more efficient, so a standard string uses only 4.8 watts.
A typical house decorated with incandescent Christmas lights uses 635 watts of electricity or 96 watts if decorated with LED lights. This includes one lighted wreath, one lighted garland, 10 strings of lights and two outdoor decorations. A heavy decorator may use up to 6799 watts when decorating with incandescent lights or 903 watts with LED lights. This includes a 500 foot c9 string, a 200 foot c9 string, 45 standard strings and one wreath.