Fluorescence is luminescence caused by a natural pigment molecule; pigments are molecules that absorb some colors of light while reflecting others. For example, green pigments (like those in leaves) absorb red and blue wavelengths of light but reflect green wavelengths. After being energized by photons (units of light energy), the electrons of some pigment molecules actually give off light as they fall back to their normal state. Chlorophyll molecules that play a role in photosynthesis have this ability, as do molecules found in several organisms, such as certain jellyfish. The body of the insect Photinus pyralis, better known as a lightning bug, has the enzyme luciferase, which generates the chemical reaction that leads to a drop in the energy state of electrons—a reaction similar to that which occurs in a chlorophyll molecule—allowing the insect to “glow” on and off during its mating season.