It's fairly stupid to rely on lights, with the attendant troubles of running out of battery power and astonishingly common failure rate under heavy use, as the sole method to keep you safe. It's even dumber to assume that you can rely upon reflectors to keep you safe.
In order to actually understand reflectors, you need to understand how they work. Reflectors do not create light, they merely bounce it in a particular direction as efficiently as possible. For normal materials like a bike frame or the fabric of a jacket, not much of the light from a car's headlights will bounce in all different directions. A bike reflector will serve to focus the light from a car's headlights directly back at the vehicle. To do this, it's a cast plastic structure that acts as a set of prisms to force light into a 180 degree turn.
Reflectors work only in certain fixed circumstances that coincidentally happen to occur fairly frequently while riding at night. They work because most motorists remember to turn on their headlights (or have automatic headlights), usually have both of them working, and therefore usually benefit from having one or more bright spots in their vision to notice that a cyclist is present.
The Consumer Safety Products Commission serves to regulate what bikes are allowed to be sold as "safe" in the US. Most of their safety guidelines were created in the 1970s and haven't been updated ever since. They created a specification for a reflector that was, at the time, the best they could come up with and haven't touched it ever since. The key part of the design is that it has three surfaces at different angles, such that, on a winding road, one of the three surfaces will have enough of an angle to be seen by the driver.
On the other hand, in varying degrees, these reflectors can be rendered useless. The big two cases are fog and when a driver's headlights are not within acceptable safe tolerance. Even though cateye reflectors on the ground are just the thing to keep drivers from riding off the road in the fog, the light has two opportunities to be absorbed by the fog instead of one, such that a normally bright reflection might be dim and away from the driver's field of view. Furthermore, and the passenger-side light being broken while overtaking a cyclist is a big example of this, a car's headlights can be bright enough to see by but not pointed right to properly light the reflector back at the driver.
The problem with plastic reflectors like a bike reflector is that you have to actually mount them correctly and in the right place. Plenty of riders unscrew the rear reflector that came with the bike so they can put a saddle bag on... and then don't bother putting anything on the saddle bag.
There's also a wide variety of micro-reflective materials. They look like tape or plastic sheeting or fabric, but if you look at them with a powerful enough microscope, they've got little coated beads or prisms. These often have different optical and mechanical properties than the plastic bike reflectors. The nicest part about them is that you can unobtrusively wrap various surfaces with reflective tape to increase the reflective possibilities of a bike. They even make black reflective tape that looks black in the daylight but reflects brilliant white back at cars.
The CPSC, even in the seventies, wasn't under any particular illusion that reflectors were actually going to make it safe to ride at night. Just that it was better than nothing and something that wouldn't add much to the cost of a bike. And, like I said earlier, it's stupid to assume that just one or the other is sufficient. Even cars are required to have reflectors as well as lights.
I tend to think, in this modern era, we could make some similarly inexpensive improvements to bike safety. I am a huge fan of the combination of a CPSC reflector and a light. See, if you remove the plastic prism of a bike reflector from the mounting, you quickly realize that the plastic on the back is just there for structural support and you can shine light through the reflector. Similarly, a few strips of reflective tape wrapped at various points around the main tubes are inexpensive and lightweight.
On the other hand, it's a political problem because the stricter you are about what bikes are allowable to be sold, the more likely people are to assume that the safety kit that comes with a bike is sufficient.
Copyright 2007, Ken Wronkiewicz