Moss that glows at night

I was out in the garden one evening with a head torch on, and noticed that the lichen or moss on the rocks was reflective, why? Johnny Crockett replies…

Q I was out in the garden one evening with a head torch on, and noticed that the lichen or moss on the rocks was reflective. I can’t find anything about it on the internet, so wondered if Crockett had any ideas.

JONNY CROCKETT replies: Different lichens contain different variations of chemicals. These chemicals can combine to either reflect or absorb different wavelengths of light. This is also known as chlorophyll fluorescence. The reason why these lichens do this is a contentious issue, but, in northern climes, it is thought that it is to reflect UV light, which could be harmful to its existence. It would be worth experimenting with different coloured filters to see which colours are reflected. I would expect blue light to be reflected more than red light.

It is also thought that by reflecting light of various wavelengths, it puts off potential browsers, and so prevents itself being eaten.