Ratio of the integrated intensities in the H_α region at 656 nm to the silicon doublet Si II–2 at 634–637 nm as a function of meteor velocity. The different showers are marked in different colours. The circles mark the cases with clearly detectable hydrogen and silicon lines. The triangles mark the upper limits of the ratio when the hydrogen line was either weak, at the noise level, or invisible and only the level of noise was measured. The line ratio corrected for afterglow contamination in one Lyrid meteor is shown as a blue cross (see Sect. 4.2).