To determine traces of oxygen as impurities, existing in conventional incandescent lamps, we investigated the emission of light caused by electric discharges. The total pressure of the gas mixture was 93000 Pa, which consists of approximately 90% of Ar, 10% of N
2, and less than 250 ppm of O
2. The spectrum decay time of Ar and N
2 did not significantly depend on the O
2 concentration, while that of O(
1S)Ar excimer formed in discharges showed a remarkable dependence; i.e., at the O
2 concentration lower than 50 ppm, R (decay constant, [1/sec]) of the excimer was proportional to the O
2 concentraiton. The measured decay time well fit the calculation using the Welge and Atkinson equation.
5) At O
2 concentrations of 50 ppm or higher, R increased with the third power of the concentration. The production of O
3 may have accelerated R. Determination of time-dependency of the excimer spectrum enabled determining O
2 in conventional incandescent lamps without destroying the envelope.
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