I'm with John on this one. Bright clothes -- yellow, blaze orange, high-vis green, or a bright red -- are going to be noticed well before a puny light. (And be-seen lights are generally pretty puny!)
The exceptions might include riding in fog, rain, or heavy overcast. Even there, bright clothes beat a be-seen light in my experience.
Note that you need to beware of confirmation bias if you're judging how soon other drivers can see you. (When you decide to test out flashing lights, you'll weight drivers slowing down much more than drivers that don't.) It's much better to note how soon you see other riders under those adverse conditions. My experience is that bright clothing and/or panniers beat lights during daytime, period. Often I'll see the bright clothes two or three times further than even the best flashing lights.
Not true, I've been saved plenty of times by my light, but mostly because it's mounted on my helmet and I can shine it back and forth directly over the drivers face.
At night you can't really make eye contact, and if they're entering the street you're on from a side street, their headlights don't pick up your reflectors or bright clothing colors until it's too late, but if you make a point of shining a light at them, the odds are much better that they'll notice.
I know this because they start to go but stop when the beam of light hits them. A blinking rear light does draw attention, and so does the reflective safety vest... The difference is that drivers have come to associate that blinking red tail light with cyclists, whereas there's all kinds of reflective things along the road. The blinky light also is visible whether or not a car's headlights are shining on you or not, whereas a reflector DEPENDS on being shined on by the headlights.
Even so, the blinky lights I've gotten seen to always break or disappear and and so do rear mounted and pedal reflectors. So I count on my reflective safety vest and the headlamp the most. I figure, from the rear, as long as I'm where I'm supposed to be, and the driver of the rear-approaching vehicle is paying attention, I won't get hit. If they AREN'T paying attention and drift onto the shoulder, I'm toast anyway, and having had a light won't have helped prevent that at all. From this perspective, I concentrate primarily on the main source of danger that I can prevent, which is cars entering the roadway from the side.
As pointed out, for any of this to work at all, the driver has to be paying attention.
I can't tell you how many times, even with my bright safety vest during the day, I've almost been hit because even though they were looking, and I thought I made direct eye contact, they still didn't SEE me.
I think, primarily, it's because they're looking for cars, not bikes, so their brain skips over a bike. Especially somewhere or at a time of day, where bikes aren't commonly seen, like a busy traffic circle.
Light or not, I ALWAYS err on the side of them NOT seeing me... Slow down to see what they do, prepared to brake or go behind them if they go, or, I time when I pass the intersection to coincide with when a car does, counting on the fact that they will see the car, even if they don't see me.
Safety aside, there's plenty of uses for a light on a tour. I also carry a little keychain light, but its not very bright if I need a light for anything serious
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