Pests are more active at night and sometimes you are only able to check on your plants when their lighst are off. It is importat not to interupt the photoperiod of the grow which is where this green flashlight comes to your aid.
 
Plants only respond to a certain colour spectrum of light and green light falls outside of it. Check your plants during dark time with no fear of disturbing the light cycle. Make sure there are no light leaks from other sources when doing so however, it doesn't take much to throw it off.