A line light source according to the present invention is provided with a plurality of external electrode rare gas fluorescent lamps, and a fixing member fixing the plurality of external electrode rare gas fluorescent lamps such that the center lines thereof are aligned. In some embodiments, multiple tests may be configured to run orthogonally within user experiences without affecting the results of one another. Other embodiments are described and claimed. The alloy thin film of the catalytically active metal and the metal capable of displacement plating has a composition comprising 5at% to 40at% of the metal.