The technology behind them has also improved. Glow stick necklaces should now last up to 12 hours (there is some variation according to colour – some colours such as green tend to be more efficient at emitting light from the chemical reaction inside). They are particularly popular with children, for obvious reason, but adults find them attractive too.
Most people will immediately think of entertainment when it comes to glow stick necklaces – bonfire night, concerts in the dark and other events. And yet, their origins were very different, and they have many other applications. They came out of the famous Bell Laboratories; founded by the inventor of the telephone, Alexander Graham Bell, the labs were formally associated with American telephone company AT&T, but more or less gave its inventors free rein to develop new ideas and technologies as they wished. The transistor, the laser and important programming languages such as C have all been amongst Bell’s outputs.
Bell’s developments in chemiluminescence – the production of light by chemical means – was quickly taken up. The earliest patent for a luminous device (the earliest forerunner of glow stick necklaces and other products) was filed in 1965. The mid-1970s saw further inventions which started to look more and more like modern glow sticks, including one that used the characteristic sealed glass vial within a plastic tube – meaning that when the glass was broken the chemicals within would mix with those outside, starting the vital chemical reaction. This device was intended, amongst other things, to be a replacement for the roadside flare. It included a stand that meant it could be thrown from a vehicle and would remain upright and at its most visible. As a flame-less technology, it was far safer than traditional flares.
Most of these inventions were associated with the US military. Further refinements took place over the next few years. One of these was a steel ball within the tube, which helped to break and mix the contents of the glass ampoule when the plastic tube was shaken. However, by the end of the 1970s the technology was essentially complete and the results were very similar to the modern glow stick. Necklaces, bracelets and other accessories would quickly follow as it was realised that there was a market far wider than the military and emergency services.
Recreation turned out to be the biggest market for chemiluminescent devices. They are still widely used by the military and in other ‘serious’ applications – such as lighting devices for divers (a sealed, flame-less light is very useful underwater). Similarly, if there is any danger of gaseous explosion then a traditional light using an incandescent filament is not safe, whether battery or mains powered. Thus glow sticks are often used after disasters as they are completely safe. They will also keep for months or even years before they are needed, and there is no danger of corrosion, as with batteries.