Christmas lights (also known as fairy lights ) are lights used for decoration in celebration of Christmas , often on display throughout the Christmas season including Advent and Christmastide . The custom goes back to when Christmas trees were decorated with candles , which symbolized Christ being the light of the world ; these were brought by Christians into their homes in early modern Germany . Christmas trees displayed publicly and illuminated with electric lights became popular in the early 20th century . By the mid- 20th century , it became customary to display strings of electric lights as along streets and on buildings ; Christmas decorations detached from the Christmas tree itself. In the United States , it became popular to outline private homes with such Christmas lights in tract housing beginning in the 1960s . By the late 20th century , the custom had also been adopted in other nations, including outside the Western world , notably in Japan and Hong Kong . Throughout Christendom, Christmas lights continue to retain their symbolism of Jesus as the light of the world .In many countries , Christmas lights , as well as other Christmas decorations, are traditionally erected on or around the first day of Advent . In the Western Christian world , the two traditional days when Christmas lights are removed are Twelfth Night and Candlemas, the latter of which ends the Christmas -Epiphany season in some denominations. Leaving the decorations up beyond Candlemas is historically considered to be inauspicious.