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
Kentucky requires lamp on the front emitting a white light visible from at least 500 feet to the front, required between one-half hour after sunset and one-half hour before sunrise. For the rear, red reflector on the rear of a type approved by the kentucky transportation cabinet, visible from all distances from 50 feet to 300 feet to the rear when directly in front of lawful lower-beam headlamps. a red rear lamp meeting the reflector's distance test may be used in addition to (but not in place of) the reflector. The rule applies whenever it is dark. See 601 KAR 14:020 (Bicycle equipment and operation).
The cheapest way to stay legal in Kentucky 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.