Simultaneous filter photometer and backscatter radar measurements during RF heating of the ionosphere (ionospheric modification) at Arecibo, Puerto Rico, in 1975 are used to relate 630.0-nm nightglow intensity modifications to F region changes. The observed ohmic heating of the F region electrons accounts for the measured 630.0-nm intensity suppression resulting from reduced 0(1D) production by 02 + ion-electron recombination. The 630.0-nm intensity enhancements caused by impact excitation of oxygen atoms by fast electrons are associated with the presence of strong plasma instabilities, as is manifested by large backscattered power from the heating wave absorption region. The variability in the RF heating wave-ionospheric plasma coupling is demonstrated by observations of suppression, no change, and enhancement of 630.0-nm nightglow intensity during similar heating cycles over a 2-hour period.