Optical emission in 1:1 binary gaseous mixtures under high voltage displays a varying character depending on pressure, applied voltage polarity, and chemical nature of the mixture. Under negative polarity, in pure N-2 and 50% mixture of Ar, O-2 and CO2, emission stemming from N-2(+) is enhanced relative to emission from neutral N-2. On mixtures of N-2 with gases containing halogens (CCl4, CHCl3, CH2Cl2, CF3H, CF2Cl2 and SF6) a reversal is observed, i.e. the N-2(+) emission is suppressed. An enhancement factor is defined as the ratio of the emission under negative polarity to positive polarity to quantify this polarity dependence. This enhancement factor varies between 0.01 and 50 depending on the second component in the mixture.