the neon billboards in the night are rather nostalgic. These billboards were very popular decades ago, and now most of them have been replaced by LED and various large screens, but this unique style is still familiar.

how do neon tubes glow? In essence, it is similar to the principle of aurora.

some kinds of thin gases, such as neon and helium, are sealed in neon glass tubes with electrodes at both ends. To make traditional neon lights, it is necessary to heat the glass tube into various shapes according to the drawings:

when the neon tube works, it is necessary to add a high enough voltage between the two electrodes (thousands of volts). Some originally neutral gas atoms will be ionized into separate electrons and positively charged ions. Under the action of high voltage, these charged particles will also be accelerated to obtain higher kinetic energy and collide with other atoms. One of the results of

collision is that the collided atom is not completely ionized, but the electrons are excited and enter the excited state with higher energy. What happens next sounds familiar: excited electrons can go back to the ground state and release the extra energy in the form of photons, so neon lights initiate light. The color of this light depends on the type of gas excited. For example, neon lights with neon gas are beautiful orange-red:

if you add fluorescent material to the inner wall of the lamp tube, you can further adjust the color of the light. Fluorescent tubes adopt the same idea.

the aurora is actually a similar process: some gas atoms in the atmosphere are hit by charged particles, enter the excited state, and emit light of the corresponding color after being excited. Only this time the charged particles come from the sun.

A relatively ugly diagram:

it just so happens that there has been an aurora burst recently. I wonder if anyone has the condition to watch _ (: ∠) _

reference: https://www.scientificamerican.com/article/how-do-neon-lights-work/

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