This fungus, the saprobe Panellus Stipticus, is displaying the type of bioluminescence known as foxfire. Foxfire is a natural form of phosphorescence.
Ylem, public domain
Foxfire is a type of luminescence displayed by certain types of fungi that decay wood. Foxfire usually is a greenish light, though reports exist of a reddish glow being emitted from some species of fungus.