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
New Hampshire requires lamp on the front emitting a white light visible from a distance of at least 300 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 300 feet to the rear when directly in front of lawful lower-beam headlamps. a red rear lamp visible from 300 feet may be used in addition to the reflector. The rule applies whenever it is dark. See RSA 266:86 (Lamps and reflectors on bicycles).
The cheapest way to stay legal in New Hampshire 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.