A bubble light is a decorative device consisting of a liquid-filled vial that is heated and lighted by an incandescent light bulb. Because of the liquid's low boiling point, the modest heat generated by the lamp causes the liquid to boil and bubble up from the vial's base. The liquid is almost always methylene chloride, but some early bubble lights used a lightweight oil. The light from the lamp illuminates the bubbles from underneath, causing them to shine.