The Reason Tonic Water Glows in the Dark

If you were to look at a gin and tonic (or vodka and tonic, or anything with tonic, for that matter) under ultraviolet light, you might be surprised to see it glow — and you might naturally wonder what produces the eerie effect.

The answer is surprisingly simple: Tonic water actually contains the chemical quinine, which fluoresces under certain light and makes tonic water glow.