Cat on my Lap

It's luciferase--an enzyme that converts chemical bond energy into light: bioluminescence. The big difference between fluorescence, which is what's occurring here and (chemi)luminescence is the source of the energy. In fluorescence, a shorter wavelength of light is absorbed and some energy is re-emitted at a longer wavelength (eg., UV light from a blacklight giving rise to blue light). With luminescence, chemical energy gives rise to the photons. This is the same process by which glowsticks work, although they use hydrogen peroxide and a chemical called luminol to provide the light.