Phosphorescence or fluorescence?
Phosphorescence and fluorescence are processes of light emission at low temperatures. In both processes, energy is absorbed and re-emitted in the form of visible light.
Phosphorescence
Phosphorescence occurs when a substance is able to absorb light produced by some external source, re-emitting it in the form of visible light, even after the lighting has been stopped . Substances of this type continue to emit a faint glow for time intervals ranging from seconds to hours.
A common example of a phosphorescent body is those residential switches that can easily be found in the dark. See the figure below, it shows a phosphorescent compass:
Fluorescence
Unlike phosphorescence, fluorescent substances emit light only while receiving energy from some external source , just like ultraviolet lamps. That way, when the energy source ceases , the fluorescence process is stopped immediately .
A good example of fluorescent objects are white lamps . These lamps contain an ionized gas inside that, when accelerated, produces ultraviolet light . On the inside of these lamps, there is a powder that contains phosphorus. This powder absorbs ultraviolet radiation and immediately re-emits it in the form of all wavelengths of visible light, producing an intense white glow that features all wavelengths of visible light (also called polychromatic light).