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.
Massachusetts requires white headlamp on the front visible from at least 500 feet, required from 30 minutes after sunset to 30 minutes before sunrise. For the rear, either an approved red rear reflector visible from 600 feet in motor-vehicle headlights, or a red rear lamp visible from 600 feet. reflectors or reflective material are also required on each pedal (or on the rider's ankles) and on each side of the bicycle, all visible from at least 600 feet — massachusetts has the strictest side- and pedal-conspicuity rules in the country. Side and/or pedal reflectors are also required. The rule applies whenever it is dark. See Mass. Gen. Laws ch. 85, § 11B (lighting subsection).
The cheapest way to stay legal in Massachusetts 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.
Massachusetts also requires reflectors beyond the core front and rear lights. New bikes from a US shop will already meet this; if you've stripped the reflectors off, replace them or add reflective tape on the frame and pedals.