Bike reflectors reflect light that shines on them from particular angles. They are typically found on the front and back of the bicycle frame, on the wheels and on the sides of platform pedals. Bike reflectors are not an adequate substitute for bright bicycle safety lights. Always use bike lights when traveling at night.
Materials
Most bike reflectors are made of hard plastic and metal or metallic plastic. Some riders use plastic reflective tape instead of or in addition to the standard reflectors; however, BikeWebsite notes that reflective tape does not meet US state legal standards for bike reflectors.
Reflection
Most objects reflect light like a mirror or by diffusing it in all possible directions. Bike reflectors send light back in the direction it came from; making the reflector appear extremely bright to someone in the same direction as the light source. However, bike reflectors also have an extremely small angle of reflection. Consumer Product Safety Commission-approved reflectors place the reflective surfaces at 90 degree angles to each other; this reflects light back in the same direction from which it came.
Reflector Types
CPSC-approved bike reflectors, required on all bikes sold in the United States, use cube corner reflectors. The 90-degree angles of the reflective surfaces form small cube shapes. Glass bead reflectors and reflector tape contain thousands or millions of tiny glass beads.
Reflector Patterns
Glass bead reflectors have a wide reflector pattern, while cube corner reflectors can have a wide or narrow pattern. A wide pattern reflector is visible from more angles and is less bright than a narrow pattern, though making the reflector larger will compensate for this. The reflectors required by the CPSC as of 2010 are small and have a narrow pattern, visible from only a few degrees of either side of the light source hitting the reflector.
Brightness
A reflector is brightest when the light shining on it hits at an angle perpendicular to the reflector. Reflectors do not work well outside just a small angle of vision. For example, a driver in a large truck or bus is several feet above the bicycle and above their vehicle's headlights. The closer the driver gets to a bicycle, the higher above the visible angle the driver is, and the less able she is to see the reflected light. Cube corner reflectors are not as bright as glass bead reflectors.
Solutions
To adhere to local laws, place reflectors on the front and/or back of your bike, but also use headlights and taillights when traveling at night. Wheel reflectors are useful only for vehicles approaching you from the side, when you are stopped. If they come loose, they can catch in your spokes and cause you to crash. Bikexprt.com's John Allen recommends using reflective ankle bands or reflective tape on your bike instead.
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