- ▁and ▁emer gency - pan els , ▁signs , ▁mark ings ▁ ▁A im ing ▁posts ▁ ▁Vari ous ▁other ▁parts ▁ ▁These ▁types ▁of ▁ph osph ores cent ▁p ig ments , ▁often ▁called ▁l ume , ▁operate ▁like ▁a ▁light ▁battery . ▁After ▁sufficient ▁activation ▁by ▁sun light ▁or ▁artificial ▁light , ▁they ▁g low ▁in ▁the ▁dark ▁for ▁hours . ▁Lar ger ▁mark ings ▁are ▁visible ▁for ▁the ▁whole ▁night . ▁This ▁activation ▁and ▁subsequent ▁light ▁emission ▁process ▁can ▁be ▁repeated ▁again ▁and ▁again , ▁and ▁the ▁material ▁does ▁not ▁suffer ▁any ▁practical ▁ag ing . ▁Str ont ium ▁al uminate – based ▁p ig ments ▁have ▁to ▁be ▁protected ▁against ▁contact ▁with ▁water ▁or ▁mo ist ure , ▁since ▁this ▁de gr ades ▁the ▁light ▁em itting ▁quality . ▁ ▁Altern ative ▁for ▁after g low ▁p ig ments ▁T rit ium - based ▁devices ▁called ▁" g ase ous ▁tr it ium ▁light ▁source " ▁( GT LS ), ▁that ▁are ▁an ▁alternative ▁for ▁after g low ▁p ig ments , ▁have ▁the ▁advantage ▁of ▁being ▁self - power ed ▁and ▁producing ▁a ▁consistent ▁lum inos ity ▁that ▁does ▁not ▁fade ▁during ▁the ▁night . ▁However , ▁they ▁are ▁radio active ▁and ▁have ▁a ▁half - life ▁of ▁slightly ▁over ▁ 1 2 ▁years . ▁ ▁This ▁means ▁the ▁intensity ▁of ▁the ▁tr it ium - power ed ▁light ▁source ▁will ▁gradually ▁fade , ▁generally ▁becoming ▁too ▁dim ▁to ▁be ▁useful ▁after ▁ 2 0 ▁to ▁