Check your state's laws (Google for "Maine bicycle laws" and you should get what you need).
In my state, the stipulated visibility equipment is required from a half-hour after sunset to a half-hour before sunrise, and in conditions where "persons and vehicles on the highway are not clearly discernible at a distance of one thousand feet ahead." (RCW 46.61.780, RCW 46.37.020). The rest of the time, you could legally ride a bike that doesn't have the safety equipment at all (in the state of Washington).