Which gas is used in most bright street signs?

Neon, which glows a distinctive orange-red when a current is passed through it at low pressure - and only that colour. Every other colour in what people call neon signage comes from a different gas or a coated tube: argon with a drop of mercury gives blue, helium pink, and phosphor coatings on the inside of the glass do the rest.

The technique is over a century old. Georges Claude demonstrated neon lighting in Paris in 1910 and the first commercial sign was a barber's in 1912; the craft of bending glass tubing by hand to form letters became a trade, and it is the reason old signs have the particular look they do. Every one is a hand-made object.

It has been almost entirely replaced by LEDs, which are cheaper, tougher and far more efficient - so the surviving tube signs are increasingly preserved as heritage rather than made new. Neon itself is also a by-product of liquefying air on an industrial scale, and a large share of the world's supply came from a small number of plants in Ukraine, which is why the semiconductor industry - which uses neon in the lasers that etch chips - had a supply scare in 2022.