White cats glow in the dark! But have you ever seen it?

News media are reporting on a study which says that cats are fluorescent and therefore they glow in the dark. But I don’t understand this report. It does not make sense to me at all. The study says that many animals emit fluorescent light. Fluorescence is the emission of light by a substance which has absorbed light “or other electromagnetic radiation”. You can see fluorescence if you illuminate an object with a UV light. In other words, fluorescent materials such as the hair of a cat emit visible light when exposed to ultraviolet light.

Note: a more interesting fact is that cat pee is fluorescent. The best way to detect if your cat has peed in your home is to shine a UV light (cheap on Amazon) on the floor or furniture at night when it is dark and the room lights are turned off. If there is urine there it will glow blue/cyan – see image below.

As I understand it, the fluorescence can only be seen with ultraviolet light. As there is no ultraviolet light at night, I cannot see the advantages of a cat being fluorescent. At night their coat will not be fluorescent. So, what are the advantages of the coat of a white cat being fluorescent? The study, by the way, says that black cats are not fluorescent and white cats are particularly fluoresecent.

The study title is: All-a-glow: spectral characteristics confirm widespread fluorescence for mammals (link). Many animals are fluorescent but have you ever seen it? The answer would be no, unless you are pointing a UV light at the animal at night and nobody does that. I have never seen my cat glow at night or in the daytime and I have never seen photos of wild cats glowing in the dark.

The scientists say that fluorescence is most common and intense in nocturnal animals, which would apply at least to a certain extent to domestic cats and the wild cat species of course. But nobody has ever mentioned before this study was published that they’ve seen a wild cat at night glowing in the dark. The point is the fluorescent quality of a cat’s coat is of no use to a cat at night because there is no UV light. That’s my understanding.

They say that 125 mammalian species are fluorescent. They decided that the lemur was not fluorescent but it requires further investigation. White fur is more fluorescent than other fur colour as mentioned. Teeth, whiskers, claws and some naked skin is fluorescent.

The scientists decided that animals are fluorescent by shining a UV light on preserved museum specimens such as a polar bear, wombat and armadillo.

They shone a UV light on a leopard skin which had been preserved and as you can see in the photograph it glowed – see photo heading this page.

During the daytime there is UV light but you’re not going to see the fluorescent effect because there’s too much white light in the daytime which masks the subtle emission of light through fluorescence.

The scientists tried to work out why fluorescence in many animals has evolved. The purpose of evolution is to allow the animal to survive more easily but it is hard to understand how fluorescence can make it easier to survive. They suggest that it might be a method of communication for nocturnal species. Or it might just be “an artefact of the structural properties of unpigmented hair”. Unpigmented hair would be white hair. I take that to mean that it just happens that some pieces of anatomy of an animal are fluorescent as a byproduct of the way they are created and that fluorescence has no particular use.

As I don’t see a use for it, I’d go along with the last suggestion.