Bubble lights have been around since the end of World War II. Their appeal lies in their ability to heat up a small amount of colored liquid to produce a unique effervescent effect.
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Bubble lights consist of long, slender vials filled with a colored liquid, with an incandescent bulb beneath the vial to heat the liquid, causing it to boil. They work best when the vial stands upright and the top of the tube is cooler than the base, allowing for an increased pressure gradient that keeps the bubbles moving. Sluggish bubble lights occasionally require tapping, after warming up, to encourage bubbling action.
Shape, Color and Sparkle
The bubble light vials are usually clear, whereas the base is made from opaque red, yellow, blue or green plastic or may be shaped like Santa's elves, snowmen or other themes. Red, yellow, blue and green liquid fills the vials, though some contain liquid and are lit by colored bulbs. A more modern trend is to add glitter, which is stirred up by the bubbles and adds extra sparkle when the bulbs are lit.
The Bubble Light Liquid
Lightweight oil initially filled bubble lights. As of 2010, the vials contain methylene chloride, which has a low boiling point for obtaining rapid bubble action when warmed.