BICYCLE LIGHTS LAW REQUIRMENTS IN Texas
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.
2005 Texas Transportation Code CHAPTER 551. OPERATION OF BICYCLES, MOPEDS, AND PLAY VEHICLES
Sec. 551.104. SAFETY EQUIPMENT.
(a) A person may not operate a bicycle unless the bicycle is equipped with a brake capable of making a braked wheel skid on dry, level, clean pavement.
(b) A person may not operate a bicycle at nighttime unless the bicycle is equipped with:
(1) a lamp on the front of the bicycle that emits a white
light visible from a distance of at least 500 feet in front of the bicycle; and
(2) on the rear of the bicycle:
(A) a red reflector that is:
(i) of a type approved by the department; and
(ii) visible when directly in front of lawful upper
beams of motor vehicle headlamps from all distances from 50 to 300 feet to the rear of the bicycle; or
(B) a lamp that emits a red light visible from a distance of 500 feet to the rear of the bicycle.