The intricacies of these requirements vary quite a bit from state-to-state; here are Arizona’s…
there is an enormous variety of opinion in “the community” about what works best for safety (“like a christmas tree”, strobe lights, etc)… this article just lays out what is required…
Here is the statute:
§28-817. Bicycle equipment
A. A bicycle that is used at nighttime shall have a lamp on the front that emits a white light visible from a distance of at least five hundred feet to the front and a RED REFLECTOR ON THE REAR of a type that is approved by the department and that is visible from all distances from fifty feet to three hundred feet to the rear when the reflector is directly in front of lawful upper beams of head lamps on a motor vehicle. A bicycle MAY have a lamp that emits a red light visible from a distance of five hundred feet to the rear in addition to the red reflector.
nighttime is defined elsewhere as “the period between sunset and sunrise” — §1-215
other notes: nobody really knows what “of a type that is approved by the department [of transportation]” means.
Note that the CPSC all-reflector system requirements apply ONLY to sale/sellers of new bicycles, and have nothing to do with state operating requirement. Notably, the CPSC requires pedal and wheel mounted reflectors, while AZ has no side or pedal requirement.
Arizona requires only a white light of certain specification MOUNTED ON THE BICYCLE. A head-mounted lamp alone does not meet the requirement.
Arizona’s statute does not address blinking or pulsing; as such it’s not clear if other than steady white light is allowed, or meet the requirement.
A red rear reflector is required! Taillights are great, but please protect yourself legally; if riding at night you are required to have a red rear reflector irrespective of having a taillight.
You can debate if that makes any sense or not– but in any event the law is the law and it will be used against you if at all possible.
Not only that, if the light fails for whatever reason, a typical reflector is quite bright; also a (not legally required but nice to have) pedal reflector can provide additional visibility advantage because of the motion.
In the pic, there are two taillights (that are off) up by the seat; down lower left is a standard CPSC red reflector, and center-right can see the amber pedal reflector… the pic was taken in a dim light, from pretty far away illuminated only with the little led on my camera/phone (it’s so grainy because it’s zoomed in, and the flash is weak).
The reflectors are highly visible so long as something is casting even a little of light their way (like headlights from an approaching vehicle).
as mentioned above, Arizona has no side requirement (even though CPSC mandates bikes be sold with side/wheel reflectors); Side reflectors are of little practical use since by the time a vehicle’s lights would illuminate a bicyclist at a right-angle threat, it would be too late for the motorist to react. (This is why a front LIGHT, and not just a reflector, is required).