BICYCLE LIGHTS LAW REQUIRMENTS IN Montana
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.
61-8-607. Lamps and other equipment on bicycles and mopeds. (1) A bicycle or moped when in use at dawn, dusk, or nighttime must be equipped with:
(a) a lamp on the front emitting a white light visible from a distance of at least 500 feet to the front. In lieu of a lamp affixed to the bicycle [or moped], a bicyclist may use a lamp with equal intensity and visibility affixed to the cyclist's helmet and facing forward.
(b) facing the rear, either a lamp emitting a red light visible from a distance of at least 500 feet to the rear or a red reflector visible from a distance of at least 500 feet to the rear when illuminated by low-beam motor vehicle headlamps; and
(c) reflective material large and reflective enough to be visible from the left and right sides from a distance of at least 500 feet when illuminated by low-beam motor vehicle headlamps.
(2) A bicycle or moped must be equipped with a brake enabling the operator to stop the bicycle [or moped] within no more than 25 feet from a speed of 10 miles an hour on dry, level, clean pavement.