Early Home Use

• Romans used lights to decoratively illuminate their homes during the winter solstice, according to the Christmas Tree Farm Network. The particular solstice celebration was the Saturnalia, a festival in honor of the agriculture god Saturnus. In addition to decorative lights, Romans bedecked their homes with greenery and also exchanged gifts. A common gift was a lamp, to symbolically illuminate the recipient's path through his life.
  
  

Tree Use

• German priest Martin Luther was the first to put lights on Christmas trees, according to the Christmas Tree Farm Network, after he saw snow-covered evergreens reflecting the moonlight one night in the 1500s. Of course, his lights were candles, which he placed on an indoor evergreen he set up to delight his children after viewing the moonlit evergreens.
  
  In 1882, Thomas Edison's assistant Edward Johnson was the first to put electric lights on a tree, according to the University of Illinois Extension.
  
  

Early Mass Production

• Although mass production of Christmas lights started in 1890, no one but the very wealthy could afford them when they first appeared, according to Wired. It took nearly 30 years for lights become affordable---and acceptable---into less wealthy homes. People were not readily willing to trust electricity inside the home at first, even though candles on trees started fires and urban department stores used Christmas lights in window displays.
  
  

Popularization

• Mass produced lights finally became popular when Albert Sadacca, who worked for his family's New York City novelty business, started selling them in 1917, according to Wired. He decided to sell the electric lights after reading a tragic story of a fire caused by candles on the Christmas tree. By that time the public was ready to trust electricity inside their home, and on their trees, and he and his brothers were behind a trade association that ruled the Christmas lights market for 50 years.
  
  

Modern Types

• Christmas lights today come in a wide variety of sizes, shapes and colors. Types include lights shaped like candles, lights clustered like garland and even tree wraps or netting speckled with dozens of lights. Strings of lights include blinking, twinkling, chasing, non-blinking or strips that feature more than one option with the flip of a switch. Large or mini bulbs are options, as are light powered by batteries rather than an electrical outlet. Novelty lights come in the shape of snowflakes, stars, chili peppers and more. Rope lights are another option, with strips of plastic roping filled with small white lights. Don't forget icicle lights that hang down like icicles from a single strand, and musical lights that play a tune as they illuminate.