In night-time auroras the intensity of highly excited (n≥3) NI line emissions is much less than 1% of the red and near-IR N21PG as well as N2+MΔv=3 band emissions, while in mid-day cusp auroras the ratio is greater than 10%. These observations point to electron impact on N (rather than on N2) as the main source of some of the mid-day auroral NI line emissions. To produce the measured level of NI 6945-51 and 6979-82A emissions, by cusp electrons impacting on N, requires the daytime polar thermospheric density of atomic nitrogen, above 200 km, in excess of 107 cm-3.