Bubble Christmas lights are decorative items that consist of a plastic tube of liquid that rises from a base with a light bulb inside. They can come on a string of several lights or separately as a tube and base that can be snapped over a regular Christmas light. Traditionally, the liquid was something with a low boiling point such as a light-weight oil or methylene chloride. The heat from the light bulb would cause the liquid to bubble, hence the term bubble lights. Modern versions typically use LED light to duplicate the effect of the bubbling liquid.
Early versions of bubble Christmas lights usually had a clear light bulb and colored liquid in the tube. There were also some versions with colored lights and clear liquid. More modern variations include glitter in the liquid, decorative bases, and lights for other holidays such as Halloween.
The color of the plastic base can also vary. Early versions of the lights usually had plastic parts that were green, red, blue, and amber. Modern bubble lights come in an even wider array of colors.
Most modern versions of Christmas bubble lights do not contain liquid, but rather have bubbles etched into the sides of the tube. The lights may be stationary or have LED elements in them that change the color in a way that imitates the way bubbles once appeared in the tube. There are also now larger bubble lights filled with distilled water that are made to be able to stand on their own.
Bubble Christmas lights have consistently existed in some form since they were first created in the 1940s. They were first made in Manchester, England, but quickly spread to other countries as their popularity grew. Bubble lights were most commonly used as decorations throughout the 1950s and 1970s, at which time they were essentially replaced by the smaller variety of light most popular throughout the rest of the century. They have since had a resurgence in popularity as a retro Christmas decoration.
The lights have been available in several sizes, voltages, and configurations over the years. Early versions of bubble lights came eight lights to a string with 15-volt light bulbs. The bulbs were screwed into a base. There are two kinds of base used for modern versions of bubble Christmas lights: a wedge base into which a 12-volt light bulb can be snapped into place or a candelabra-style base that accepts 120-volt light bulbs.