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
Alabama requires white lamp on the front, visible from a distance of at least 500 feet. For the rear, red reflector on the rear visible from all distances from 100 to 600 feet when directly in front of lawful upper-beam headlamps. a red rear lamp visible from 500 feet may be used in addition to (but not in lieu of) the reflector. The rule applies whenever it is dark. See Ala. Code § 32-5A-265 (Lamps and other equipment on bicycles).
The cheapest way to stay legal in Alabama 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.