BICYCLE LIGHTS LAW REQUIRMENTS IN Virginia
In US the bike lights die required by Law if you reading in low light conditions, The light can be attached to either the bike or to the cyclist but must be visible at least 500 feet to the front of the bicyde, so be careful how you position the light. Additional lighting must be consistent with the law specifying required lights and reflectors, so a rear light must be red.
2006 Code of Virginia § 46.2-1015 - Lights on bicycles, electric personal assistive mobility devices, electric power-assisted bicycles…
A. Every bicycle, electric personal assistive mobility device, electric personal delivery device, electric power-assisted bicycle, moped, and motorized skateboard or scooter with handlebars when in use between sunset and sunrise shall be equipped with a headlight on the front emitting a white light visible in clear weather from a distance of at least 500 feet to the front and a red reflector visible from a distance of at least 600 feet to the rear when directly in front of lawful lower beams of headlights on a motor vehicle. Such lights and reflector shall be of types approved by the Superintendent.
In addition to the foregoing provisions of this section, a bicycle or its rider may be equipped with lights or reflectors. These lights may be steady burning or blinking.
B. Every bicycle, or its rider, shall be equipped with a taillight on the rear emitting a red light plainly visible in clear weather from a distance of at least 500 feet to the rear when in use between sunset and sunrise and operating on any highway with a speed limit of 35 mph or greater. Any such taillight shall be of a type approved by the Superintendent.