Results of the continuous measurements of O I 630.0-nm dayglow from Mount Abu (20¿ 20' N dip latitude), a station in the region of equatorial ionization anomaly (EIA) by means of a recently developed ground-based dayglow photometer are presented. The measurements on magnetically quiet and moderately active days reveal that there are strong noontime bite-outs in 630.0-nm intensities. the temporal variabilities in the intensities show a good correlation with those in electron densities in the lower F region over Ahmedabad (18¿ 23' N dip latitude) with a time delay of 1 hour. Theoretical estimation of the intensities indicates that the dissociative recombination of O2+ with ambient electrons is mainly responsible for the observed temporal variability in the dayglow emission. The time delay between the theoretically evaluated and the measured noontime bite-outs is discussed in the context of the development of the EIA. ¿ American Geophysical Union 1992