LEDUP LED Holiday Light Strings have many features and benefits not found on other LED Christmas string on the market. The most noteworthy aspect of LEDUP LED strings is a new INTERCHANGEABLE bulb feature combined with our balanced circuit design. For example: A customer can buy 1 BLUE string and 1 WHITE string and switch every second bulb to get the custom look of a BLUE/WHITE combination they could never find in a retail store. The special stay lit circuit design ensures continuous operation even if a LED bulb prematurely fails. Simply remove the burned out bulb and replace with one of the two spare bulbs included in the box.