Originally Posted by CTAC
If you have a car nearby with tail lights on, producing 10W of light the reflector will not be seen.
Another point of view (from the CPSC's
BICYCLE REFLECTOR PROJECT):
The CPSC staff was not aware of any quantifiable correlation between photometric performance and a motorist's ability to see and avoid a hazard. Therefore, laboratory photometric testing alone could not be used to evaluate a bicycle reflector system. The most feasible evaluation would be to compare the relative performance of the reflectors that met the CPSC regulation to other types of bicycle conspicuity treatments through field-testing.