Phosphorescent materials are those that can absorb energy when excited by solar, fluorescent and other artificial lights. In particular, when these materials are excited by ultraviolet light, they deviate from their initial equilibrium states, and convert the absorbed energy to visible light after they return to the equilibrium states so as to continue to glow after the excitation has stopped. Material which can maintain a long glowing time is referred to as a "long afterglow phosphor".
Luminous paints applied on watch dials and safe marks have usually been formed by admixing phosphorescent material, using zinc sulfide mixed with copper (ZnS:Cu) as an activator, into paint, ink and the like. The sulfides can absorb energy when excited by ultraviolet light with certain wavelengths and then release the energy in theI’ve witnessed the self-assured superiority of Paris, the imperial arrogance of Washington, the capitalist decadence of New York’s Manhattan, parliamentary elections in Germany, and my fair share of elections in Britain. In none of them have I encountered a democratic political culture as profound as Venezuela’s.

In Venezuela it’s hard to avoid politics at the best of times, but during election campaigns signs of political struggle and debate become, quite literally, wall to wall. In the small Andean city of Merida, with a population of under 300,000, a walk across the city centre gives an idea of the intensity of the campaign being waged ahead of the 7 October presidential election. With socialist President Hugo Chavez seeking a third term in office against right-wing challenger Henrique Capriles Radonski for