This guide is for general information only and is not legal advice. Laws change — verify current rules with your state DOT or a licensed attorney before relying on this for any legal matter. Read full disclaimer.
The rule
Maine requires lamp on the front emitting a white light visible from a distance of at least 200 feet to the front, required from one-half hour after sunset to one-half hour before sunrise. For the rear, red reflector on the rear visible from at least 200 feet when directly in front of lawful lower-beam headlamps. a red lamp on the rear visible from 200 feet may be used in addition to the reflector. The rule applies whenever it is dark. See 29-A M.R.S. § 2068 (Equipment required on bicycles).
The cheapest way to stay legal in Maine is a USB-rechargeable front white light and a rear red light or reflector that meets the spec above. A $30 light set covers it.