A bubble light is a decorative device consisting of a liquid-filled vial that is heated and lighted by an incandescent light bulb

Incandescent light bulb

The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process...

. Because of the liquid's low boiling point

Boiling point

The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

, the modest heat generated by the lamp causes the liquid to boil and bubble

Bubble

-Physical bubbles:* Liquid bubble, globule of one substance encased in another, usually air in a liquid* Soap bubble, a bubble formed by soapy water * Antibubble, a droplet of liquid surrounded by a thin film of gas-Arts and literature:...

 up from the vial's base. The liquid is almost always methylene chloride

Dichloromethane

Dichloromethane is an organic compound with the formula CH2Cl2. This colorless, volatile liquid with a moderately sweet aroma is widely used as a solvent. Although it is not miscible with water, it is miscible with many organic solvents...

, but some early bubble lights used a lightweight oil

Oil

An oil is any substance that is liquid at ambient temperatures and does not mix with water but may mix with other oils and organic solvents. This general definition includes vegetable oils, volatile essential oils, petrochemical oils, and synthetic oils....

. The light from the lamp illuminates the bubbles from underneath, causing them to shine. As Christmas lights, bubble lights were very popular during the 1950s through and including the 1970s, before miniature "fairy" lights became popular.

Bubble lights were being manufactured by the Telsen Electric Co.(1935) Ltd

Telsen Electric Company Ltd

Telsen Electric Company was a British electronics company formed in Birmingham in 1924 by Mr A. Macnamara at 207 Aston Road.In 1930 they moved to 56 Miller Street and shortly after moved to their new factory at the corner of Philips Street and Thomas Street....

, in Manchester, England, possibly as early as the late 1920s. Bubble lights for Christmas

Christmas

Christmas or Christmas Day is an annual holiday generally celebrated on December 25 by billions of people around the world. It is a Christian feast that commemorates the birth of Jesus Christ, liturgically closing the Advent season and initiating the season of Christmastide, which lasts twelve days...

 decoration were patented in the United States by Carl W. Otis in 1944 and introduced to the US in 1946 by Noma

NOMA (company)

NOMA was an American company best known for making Christmas lights. It was once the largest manufacturer of holiday lighting in the world, but since 1967 has existed only as a licensed trademark...

, one of the largest American manufacturers of Christmas lights. While Noma was the largest company to make these lights, other manufacturers included Sterling, Royal Electric Company and Good Lite.

Bubble lights of all kinds operate best when the top of the tube is significantly cooler than the bottom, thus increasing the pressure gradient

Pressure gradient

In atmospheric sciences , the pressure gradient is a physical quantity that describes in which direction and at what rate the pressure changes the most rapidly around a particular location. The pressure gradient is a dimensional quantity expressed in units of pressure per unit length...

. The tubes must be kept upright, and occasionally need to be tapped or even shaken to begin bubbling after warming up.

Bubble lights have been made in two different base sizes: E10 (C6) 15 volt, and E12 (C7). The original design used a miniature screw base (E10), such as those used on C6 cone Christmas lamps. These early designs were nominally designed to operate with eight on one string, in series, at 15 volts each. However, they were often packaged with a nine-socket string to extend the life of the bulbs. Bubble lights could also be purchased individually for use in an already-owned light string. Modern incarnations either use candelabra

Candelabra

"Candelabra" is the traditional term for a set of multiple decorative candlesticks, each of which often holds a candle on each of multiple arms or branches connected to a column or pedestal...

 base (E12) 120-volt bulbs, or push-in wedge base

Wedge base

A wedge base is a type of electrical connector used as a fitting for small light bulbs. It is similar to the bi-pin connector, except that the two "pins" are the same wires that extend into the bulb , and the wires are bent up onto the sides of the base, where they make contact with the socket...

 "midget" size miniature bulbs (most commonly ten 12-volt bulbs wired in series).

The clear light bulb is enclosed in a plastic base made up of a "bowl" and a "cap", usually of different colors. Bubble lights are manufactured in just about any color, including the liquid in the tube. The plastics used are most commonly semi-opaque red, yellow, blue, and green. Liquids are generally amber, red, blue green ,and rarely purple and pink. Uncolored liquid is also available, being lit with colored bulbs instead.

In recent years, bubble lights have become more elaborate in appearance. Glitter

Glitter

Glitter describes an assortment of very small pieces of copolymer plastics, aluminum foil, titanium dioxide, iron oxides, bismuth oxychloride or other materials painted in metallic, neon and iridescent colors to reflect light in a sparkling spectrum...

 is sometimes added to the vials for extra sparkle, most commonly on specialty types such as those used in decorative night-lights. Bases are now often made to look like objects such as Santas or snowmen, rather than the plain ribbed plastic. Like many other Christmas decoration

Christmas decoration

A Christmas decoration is any of several types of decorations used at Christmastime. The traditional colours of Christmas are pine green , snow white, and heart red. Blue and white are often used to represent winter, or sometimes Hanukkah, which occurs around the same time. Gold and silver are...

s, they have been converted for Halloween

Halloween

Hallowe'en , also known as Halloween or All Hallows' Eve, is a yearly holiday observed around the world on October 31, the night before All Saints' Day...

 use, usually with orange liquid and a base that looks like a jack-o-lantern, or the head of a black cat

Black cat

A black cat is a feline with black fur. It is not a particular breed of cat and may be mixed or of a specific breed. The Bombay, known for its sleek black fur, is an example of a black cat. The all-black pigmentation is equally prevalent in both male and female cats...

 or witch, among other Halloween symbol

Symbol

A symbol is something which represents an idea, a physical entity or a process but is distinct from it. The purpose of a symbol is to communicate meaning. For example, a red octagon may be a symbol for "STOP". On a map, a picture of a tent might represent a campsite. Numerals are symbols for...

s.

Modern imitations of bubble lights are made from acrylic or other clear plastic rods, with permanent bubbles deliberately manufactured into them, lit with fixed-color or color-changing LED

LEd

LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....

s. Other bubbling lights are much larger and sit on a table or floor, occasionally with fake fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

 which "swim

Aquatic locomotion

Swimming is biologically propelled motion through a liquid medium. Swimming has evolved a number of times in a range of organisms ranging from arthropods to fish to molluscs.-Evolution of swimming:...

" up and down in the changing buoyancy

Buoyancy

In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...

. These tubes are filled with distilled

Distillation

Distillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....

 water and have one or more airstone

Airstone

An airstone, also called an aquarium bubbler, is a piece of aquarium furniture, traditionally a piece of limewood or porous stone, whose purpose is to gradually diffuse oxygen into the tank, eliminating the noise and large bubbles of conventional air filtration systems, and providing other benefits...

s at the bottom, and normally a light, along with the air pump

Air pump

An air pump is a device for pushing air. Examples include a bicycle pump, pumps that are used to aerate an aquarium or a pond via an airstone; a gas compressor used to power a pneumatic tool, air horn or pipe organ; a bellows used to encourage a fire; and a vacuum pump.The first effective air pump...

.