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	A '''lava lamp''' is a ] typically used for decoration rather than illumination. The gentle flow of randomly-shaped blobs of wax suggests the flowing of ]. The lamps are available with a wide variety of container styles and colours of wax and liquid.
	==How it works==
	The lamp consists of an illuminating bulb which heats up the lamp's contents, a glass bottle containing a transparent oil and ] wax (although other combinations may be used), alcohol, and a metallic wire coil. The glass bottle sits on top of the bulb. The metallic wire coil is hidden in the base of the lamp, on which the glass bottle is sitting.

	The wax is slightly ''more'' ] than the oil at room temperature, and slightly ''less'' dense than the oil under marginally warmer conditions. This happens because the wax expands ''more'' than the oil when both are heated.

	When the lava lamp is turned on, the light bulb heats the bottom of the glass bottle which in turn heats the contents of the glass bottle in this vicinity.

	Wax at the bottom heats until it melts, and eventually becomes less dense than the liquid above it. At this time, a portion of the wax rises towards the top of the container. Near the top, away from the heat source, the wax cools, contracts, and as its density increases it begins to fall through the liquid towards the bottom of the container again. This is a ], visible form of ] heat transfer, although it also occurs on a molecular scale within the liquid itself. The difference in temperature between the top and bottom of the globe is only a few degrees.

	One mass of wax may rise as another falls. The metal coil at the bottom helps to overcome the ] of the individual wax droplets, causing the descending blobs to ] into a single molten wax mass at the bottom of the container. The cycle of rising and falling wax droplets continues so long as the bottom of the container remains warm and the top of the container remains cool. Operating temperatures of lava lamps vary, but are normally around 60 ] (140 ]). 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 all rising to the top (too hot).

	] behavior makes the movement of the wax unpredictable—hence lava lamps can be used as a physical ].

	==History==
	{{main article\|Edward Craven Walker}}
	An Englishman, ], invented the original and best-known lava lamp in the ]. His U.S. patent 3,570,156 for "Display Device" was filed in ] and issued in ]. He named it the "Astrolight" or "Astro Lamp" and presented it at a ] trade show in ], where the entrepreneur Adolph Wertheimer noticed it. Wertheimer and his business partner Hy Spector bought the ] rights to the product and began to produce it as the "Lava Lite" via a corporation called Haggerty Enterprises and trading under the name .

	The lava lamp became an ] of the ], where the constantly changing, brightly-coloured display has been compared to the ] hallucinations of certain popular recreational ]. In the ] Mr. Walker sold his rights to Cressida Granger whose company ] continues to make lava lamps and other related products.

	Lava lamps were also featured in an episode of the TV show '']'', in which it was ] that heating a lava lamp on a stove could cause the lamp to explode, and injuries sustained from such an explosion could be fatal.

	==See also==
	*]
	*] a patent for generation of random numbers using lava lamps

	==External links==

	{{Commons\|Lava lamp}}
	* Extensive lava lamp fansite which includes discussion forums, history, formulas, and vintage lamp gallery.
	* referenced above.
	*
	* How to take care of and fix common problems with a lava lamp.
	* (from ])
	* (from ])
	*


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Revision as of 17:49, 18 June 2007