Ripe bananas glow blue in ultraviolet light.
Like many fruit, unripe bananas are green because they're still full of chlorophyll. In bananas, that chlorophyll breaks down into a UV reactive pigment.
Some birds and insects are tetrachromats, and can see UV light. To them, bananas which are ripe and ready to eat are super obvious, and easy to see from the air.
@InvaderXan I appreciate the wavelength being given in nanometers in that pic, because "blacklight" and "UV" are very broad categories. For example, the UV lights I use to cure 3d prints wouldn't make these bananas glow like in that photo.
@bunny_jane Yes, very true. I think it's easy to not realise what a broad category "ultraviolet" is. I mean, seeing as you can't see it and all.
Though in fairness, with things like this, you only have a useful range of around 300-400 nm. Anything shorter than 300 gets absorbed rapidly by the atmosphere.
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