Dependence of the spectral intensity ratio of N III on electron density. The double-dot-dashed line represents the ratio of the transition intensity from 2s¹2p^{2 4}P_1/2 to 2s²2p^{1 2}P_3/2 to that from 2s¹2p^{2 4}P_5/2 to 2s²2p^{1 2}P_3/2 (R1). The dashed line represents the ratio of the transition intensity from 2s¹2p^{2 4}P_3/2 to 2s²2p^{1 2}P_3/2 to that from 2s¹2p^{2 4}P_5/2 to 2s²2p^{1 2}P_3/2 (R2). Different colors correspond to different energy distributions.