Originally Posted by
cyccommute
While it is true that the reflector is more efficient than a mirror and light coming from the left won't be reflected to the right, the angle of incidence is still important and narrow. If the light source is too far off axis, it won't reflect back or even hit the reflecting surface. To use your analogy of a ball thrown into the corner, if you miss the corner, the ball doesn't rebound back towards you.
And reflectors are mostly useless during daylight hours. They still reflect light but the ambient light overwhelms it.
Don't think anyone has claimed that reflectors are at all effective during daytime. Main problem is again that they reflect light back to the source. If that source is the sun then the reflected light goes back in that direction. That's going to be up in the sky somewhere - not where a motorist is going to see it.
And sure, if the driver's headlight beam completely misses your reflector then there won't be any light for it to reflect. But reflectors are still much more effective than that article would have us believe. I'd never depend on them alone, but they make a very cheap and lightweight backup to active lighting systems.