Lava lamp

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A lava lamp is a novelty item typically used for decoration and ambience rather than illumination; the slow albeit chaotic rise and fall of the randomly-shaped blobs of wax is fancifully suggestive of the flow of lava, hence the name. The lamps are available with a wide variety of container styles and colors of wax and liquid. They rose to prominence in the late 1960s and early 1970s and are often associated with the hippie movement of that period.

1 How it works
2 History
3 Hazards
4 See also
5 References
6 External links

[edit] How it works

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The lamp consists of an incandescent bulb which heats the contents of a tapered glass bottle containing water and a translucent mix of wax and carbon tetrachloride (although other combinations may be used). A metallic wire coil which is hidden in the base of the lamp both furthers the necessary heat convection and suspends the falling blobs of liquid wax.

The wax is slightly denser than the water at room temperature, and slightly less dense than the water under marginally warmer conditions. This occurs because the wax expands more than the water when both are heated.

While common wax is much less dense than water and would float in it at any room temperature, a heavy, nonflammable solvent is added to tune the wax density to be just slightly higher than that of water.

Wax at the bottom heats until it melts, eventually becoming less dense than the liquid around it; portions of wax thus overcome their surface tension and rise. Near the top, away from the heat source, the wax cools and contracts, and as its density thus increases it begins to fall.

The lava lamp owes its classic shape to physics as much as aesthetics: at the tapered end there is more surface area per unit volume of liquid, hence the liquid in that area undergoes a higher rate of cooling than the liquid nearer the bottom. The whole process is a macroscopic, visible, form of convection heat transfer, although it also occurs on a molecular scale within the liquids themselves. The difference in temperature between the top and bottom of the lava lamp, as with a Galilean thermometer, is only a few degrees.

While the fluctuating wax spheroids frequently collide as they rise and fall, they do not cohere in transit insofar as they regain sufficient surface tension. The heat source at the bottom, most specifically the heat coil, overcomes surface tension of the individual wax blobs. This causes the descending individual blobs of wax to coalesce into the single liquid wax mass at the bottom of the container.

The cycle of rising and falling masses of colorful wax continues for as long as the temperature differential remains sufficiently great. Operating temperatures of lava lamps vary, but are normally around 60 °C (140 °F). If too low or too high a wattage bulb is used in the base, the "lava" ceases to circulate, either remaining quiescent at the bottom (too cold) or virtually all of it rising to the top (too hot).

Sensitivity to initial conditions renders the manifold characteristics of the wax blobs (their phase shifts, size, speed, number, currents, protean forms, varying viscosity, collisions, etc.) sufficiently unpredictable to serve as an excellent if fanciful example of chaos theory in action. The Lavarand system used this unpredictability as the basis of a notable hardware random number generator.

[edit] History

An Englishman, Edward Craven Walker, invented the original and best-known lava lamp in the 1960s. His U.S. Patent 3,570,156 for "Display Device" was filed in 1965 and issued in 1968.[1] Walker's company was named Crestworth and was based in Poole in the United Kingdom.

Walker named the lamp Astro and had various variations such as the Astro Mini, the Astro Coach lantern and presented it at a Brussels trade show in 1965, where the entrepreneur Adolph Wertheimer noticed it. Wertheimer and his business partner Hy Spector bought the American rights to the product and began to produce it as the "Lava Lite" via a corporation called Lava Simplex International, which is the origination of the use of the term "lava" in conjunction with this sort of lamp. Wertheimer dropped out of the development of the product, while Spector went on to manufacture and market the "Lava Lite" in his Chicago factory in the mid-60's. The lamps were a huge success nationwide throughout the rest of the '60s and early '70s.

The lava lamp became an icon of the 1960s, where the constantly changing, brightly colored display has been compared to the psychedelic hallucinations of certain popular recreational drugs, particularly LSD. Lava Simplex International also produced the "Wave Machine", the "Gem Light", the "Timette Wall Clock" and the "Westminster Grandfather Clock".

In 1986, Hy Spector sold Lava Simplex International to Eddie Sheldon and Larry Haggerty of Haggerty Enterprises. Haggerty Enterprises continues to produce and sell the Lava Lamp product line in the US, using the name of Lavaworld. "Lava lamp" has been widely used as a generic term for this sort of lamp, but Lavaworld has claimed such usages to be a violation of its trademarks.[2] Lavaworld has since closed their production facilities in the USA and have outsourced their lamps to mainland China.

In the 1990s, Mr. Walker, who has the rights to England and Western Europe, sold his rights to Cressida Granger whose company, Mathmos, continues to make Lava Lamps and other related products. Mathmos lava lamps are still made in the original factory in Poole, Dorset where they were first made.

[edit] Hazards

An episode of the TV show MythBusters demonstrated that heating a lava lamp on a stove could cause the lamp to explode, and injuries sustained from such an explosion could be fatal.^[1] The inspiration for that experiment came from a news story concerning a Kent, Washington, man who in 2004 died after a lava lamp that he was heating on a stove (in order to bypass the time delay associated with heating the wax) exploded, sending glass shards into his chest.^[2]