| http://www.w3.org/ns/prov#value | - The self-luminous light sources 2 are of the type described above; i.e. they each comprise a glass or other transparent shell coated with radioluminescing phorphor and filled with tritium gas or other radioactive material, e.g. as shown in the Clapham, U.S. Pat. No. 3,409,770.
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