The northern European custom of the candlelit Christmas tree is derived from the belief that it sheltered woodland spirits when other trees lost their leaves during winter. The tradition of Christmas lights dates back to when Christians were persecuted for saying Mass. A simple candle in the window meant that Mass would be celebrated there that night. Electric Christmas tree lights were first used in 1895. An American, Ralph E. Morris, wanted something safer than the traditional candles.

	Why do all your Christmas lights stop working just because one is broken?
	Turn your Christmas lights on. Do they all work?
	Turn your Christmas lights off and unplug the plug. Gently remove one of the bulbs from your string of lights. Now plug the string of lights back in and turn them on. Do they still all work?
	If not, here’s why. Electricity needs a complete circuit to flow. If you make a break in any part of the circuit then the electricity can't flow and the lights won't work. A broken bulb is essentially the same as breaking the circuit - no electricity can flow along the wire. This means none of the lights can work.
	If they do still work, here’s why. Electricity needs a complete circuit to flow, but your lights have been specially made so that a broken bulb won't break the circuit. These lights work by giving the electricity an alternative route past each light. It's as though each bulb has a bypass around it - if the bulb is broken, the electricity can still get to the other lights.
	When you have finished, remember to turn the lights off at the wall, unplug them and gently replace the bulb you removed.
	For loads more information: http://www.cvc.org/christmas/electric_xmas.htm http://www.howstuffworks.com/christmas-lights.htm