Part Four of our "Christmas Explained" series deals with lights on the house. Why do we go out in the cold and in the wind to put strings of lights up on our house?

The simple answer is Edison. To be more specific, it was Edward Johnson who was working with Edison at the time.

Edison started off working for Johnson. When Edison left that job to start his own company, Johnson went with him.

When Christmas started to roll around in 1880, Johnson had the "bright" idea (pardon the pun) to replace candles on trees with Edison's light bulbs. The candles were an obvious fire hazard, and the light bulbs could be used as a better alternative.

He strung about 80 of them together and placed them on a tree before calling reporters to come see. The lights were red, white, and blue. The tree was placed in a window and everyone had to stop and see the display.

It would take some time for the trend to catch on. The bulbs were expensive and not everyone had access to electricity.

In 1894, President Cleveland put electric lights on the White House Christmas tree. The price would come down in 1914 enough to be affordable. By the 1930s, Christmas lights were everywhere.

The lights would make a jump from being just on trees to being wrapped around pretty much anything.

I guess you could say that this tradition is one born out of necessity, and then competition. Nothing gets neighborhood rivalries going more than Christmas displays. They're the winter equivalent to having the nicest lawn on the street.

So this year when you're stringing lights, thank Edison. Or better yet, thank Edward Johnson for making you pull out the ladder and staple gun.