In order to develop an economical pest-control lighting system for two noctuid species, Helicoverpa armigera and Mamestra brassicae, we investigated the daily activity of these two species with illumination at night. The compound eye spectral sensitivity of the two moths showed peaks at 360 nm and 500—550 nm. We selected green LED peaking at 535 nm for the lighting device, because this wavelength has little effect for plants. The light intensity was 2.5×1017 photons·m-2·s-1 at a distance of 10 cm from the light source. We recorded the activities of moths using an actograph, and compared the activities at night with and without the green illumination. Continuous illumination at night reduced the activities most effectively in both species. While a 0.2 Hz flickering condition (0.5 sec ON and 4.5 sec OFF) significantly suppressed the activity in H. armigera, no significant effect of flickering light was detected in M. brassicae.