Why do neon streetlights glow

Neon lights are commonly seen on advertising hoardings, outside shops, restaurants, and cinemas. Their colour is so distinctive that to most people the word neon has come to mean a dark pink glow, although neon is merely an elemental rare gas (element number 10). 

This difference between absorption and emission is crucial, and underlies many of pivotal aspects of photochemistry. We will look in depth at the underlying photochemistry of neon in Section 9.3. 

At its simplest, photochemical absorbances involve the uptake of photons, so the number of photons leaving a sample will be less 

The word light here does not just mean visible light, but all wavelengths. 

The light striking the sample is called the incident light. 

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