Glowla

Meet Glowla, a fluorescent molecule who drinks in ultraviolet light and glows back in visible colour.

A fluorescent molecule absorbs a photon and jumps to an excited electronic state. Before it emits, it quickly loses a little energy to vibrations and its surroundings. It then drops back down, emitting a photon within nanoseconds. Because some energy was lost on the way, the emitted photon has less energy, and so a longer wavelength, than the one absorbed. George Gabriel Stokes described this in 1852, and the difference is called the Stokes shift.

So invisible ultraviolet can come out as visible blue, green or yellow. Highlighter ink and 'black light' posters glow this way.

Fluorescent lamps coat their tubes with phosphors that turn the ultraviolet from mercury vapour into visible light. White LEDs use a phosphor to turn blue light into yellow. In biology, fluorescent dyes and proteins light up specific parts of cells under the microscope.

Fluorescence stops almost as soon as the light is switched off. Glow-in-the-dark materials use a different, slower process, phosphorescence. Strong light can also bleach fluorescent molecules over time.