Science At Work: How Does A Lava Lamp Work?

Over the past several hundred years, we have seen how Science and its special fields of Physics and Chemistry have led to the improvement of modern living by leaps and bounds. Arguably, one of the most unique items that show science at work is the popular lava lamp.

So, how does a lava lamp work?

The lava lamp consists of a tall glass vessel (which is usually in the shape of a cylinder) containing water (with glycerol derivatives and other additives) and wax, which can be transparent, translucent or opaque. The wax is often mixed with carbon tetrachloride or other chemical substances.

The underlying scientific principle behind the lava lamp is the Rayleigh-Taylor Instability. Following fluid mechanics, you have an unstable interface that separates two fluids of different densities. Because of this instability, the fluid with the lighter density is accelerated toward the heavy fluid.

While you may initially think of wax as a solid, remember that heat causes the wax to melt. A good example is candles. What happens inside a lava lamp is that you have a standard incandescent bulb or halogen lamp of 25 to 40 watts which heats up the blobs of wax that are at the bottom of the lamp. The heat causes the wax to melt (decreasing its relative density), so that blobs begin to ascent to the top of the glass cylinder. As they near the surface, the wax blobs start to cool thereby increasing their relative density. As the wax solidifies, it once again sinks to the bottom of the cylinder where it is again reheated.

A metallic wire coil found at the lamp bottom helps to break the surface tension to allow for recombination of the cooled wax blobs. The various shapes – ranging from blobs to ropes to entrails – that the wax takes as it rises and descends greatly resemble pahoehoe lava, from the name of the lamp has been derived.

If the lava lamp is placed in an ideal setting in the home, it will usually take 45 to 60 minutes to sufficiently warm up the wax so that it begins to rise. However, if it has been placed in a cold, air-conditioned room and has not been used for some time, it may take 2 to 3 hours to heat it up. Inadequate heating may cause the wax blobs to just simply float at the bottom of the cylinder, creep up along the sides, or break up into very small globules.

Because lava lamps utilize an unstable fluid mechanics system, you should be extra careful that it does not be knocked over or, worse, shaken. These two “accidents” can cause the water/fluid and wax inside the lamp to emulsify, so that your lava lamp becomes cloudy.

Lava lamps have a “cousin” lighting fixture in the form of the Glitter Lamp. Unlike the lava lamp, the Glitter Lamp is so named for the glitters that are placed inside the glass cylinder in place of wax. Instead of rising up and down, these glitters move in a circular motion inside its glass vessel.

See Science at work by doing research on the topic, “How does a lava lamp work?”