As a kind of new electric light source, electrodeless discharge lamps (EDL) are based on high-frequency electromagnetic induction and nonpolar gas discharge. Visible light is emitted as a result of Hg 253.7 nm resonance spectrum line inspiring phosphor. The influence of indium net position on the Hg 253.7 nm resonance spectral line was studied experimentally by atomic emission spectral analysis. It was found that the relative intensity of Hg 253.7 nm resonance spectral line is strongest when the indium net is located at both ends of coupling coil, weaker at middle and weakest when far away from coupling coil. It was inferred that there is an optimum indium net position for EDL, and the corresponding lighting effect is maximal. The results were qualitatively analyzed from the standpoint of gas discharge theory, combined with the finite element simulation of Maxwell 3D, which has instructive value for pattern design and parametric optimization of EDL.