As I mentioned above, shining your own light on retroreflective material of any kind will have an effect similar to that that you see when it is illuminated under indirect daylight. All of the light from your flashlight reflected by your vest will be aimed right back at your flashlight - not at approaching drivers. Please see John Allen's page on reflectors for a more detailed treatise on the subject.

Where this may have some effect is if you use something like a Class II construction worker's fluorescent safety vest, in which case your light may light up the fluorescent vest before the driver's own headlights under some circumstances.

If you want to see the effect that the light has on visibility, try having someone ride your bike away from you whilen wearing your vest and with the light on three times:

1. With you standing in darkness. This is to simulate the situation in which the driver's lights don't illuminate you at all, a situation I suspect is rarely going to be the case when they need maximum reaction time. Note that this should overstate the benefit of the light because your eyes will probably be much more dark adjusted than the driver's eyes.

2. With you standing next to a car with its headlights on and pointed at your retreating bicycle. You should be standing six feet (6') from the headlight nearest you. This simulates a car coming up behind you with its driver's side headlight out.

3. With you preferably seated in the driver's seat or a similar position relative to the headlight. This is what is going to be seen most of the time.

All this being said, if considering this you feel it is worth your time, money, and trouble, I think it is perfectly fine. I just think the proposed benefits I see in this thread overstate the real benefit.

Tor