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IN THE 1850s, glass-makers in Bohemia invented a new type of glass by adding small amounts of uranium ore. Not only was the glass a striking greenish-yellow colour, it also appeared to glow in the evening sun. It became very fashionable, and was used in all manner of glassware from jewellery to fruit bowls (see picture). What no one knew at the time was that it was radioactive, and the green glow was caused by fluorescence.

Fluorescence is an optical phenomenon that occurs when light absorbed by a material excites the molecules in it and causes them to emit light of a longer wavelength. In the case of a strip light, for example, ultraviolet light from the bulb is converted into the white light that we see by a fluorescent powder that coats the inside of the glass. Many common substances fluoresce under UV light: teeth, cheese, amber, quartz, chlorophyll, some vitamins, quinine in tonic water and the cuticles of scorpions, to name a few.

You can see examples of all this at AfterImage, an exhibition exploring the science of colour perception at the Hayward Gallery in London. It is part of a retrospective of the works of Dan Flavin, the New York artist best known for making extraordinary and beautiful installations from everyday fluorescent strip lights. The exhibition runs until 2 April (see ).

One of the aims of AfterImage is to show that there’s a lot more to fluorescence than strip lighting, and to illustrate its many uses. For example, it helps jewellers identify poor-quality diamonds by showing up any impurities, and mail companies use fluorescent barcodes to help them sort the post. White paper is treated with fluorescent compounds to make it appear whiter, and the isolation of a compound found in jellyfish called green fluorescent protein has revolutionised the field of molecular biology. Genetic engineers now routinely use it to monitor gene activity in cells.

Meanwhile, fluorescent strip lights – like uranium glass – could soon be a thing of the past, superseded by LED technology. Enjoy them while you can.