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
Utah requires lamp on the front emitting a white light visible from a distance of at least 500 feet to the front. For the rear, red reflector on the rear visible from all distances from 100 to 600 feet to the rear when directly in front of lawful lower-beam headlamps. a red rear lamp visible from 500 feet to the rear may be used in addition to the reflector. The rule applies whenever it is dark. See Utah Code § 41-6a-1114 (Bicycle equipment — lamps and reflectors).
The cheapest way to stay legal in Utah 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.