No one is claiming that having lights is going to prevent all accidents. Doesn't matter what you do you can't control fate, accidents happen. This doesn't mean you throw out all preventative measures. Forget looking for data or someone who did a study. Cars have full lights and get in accidents all the time. On the other hand they are more exposed to accidents because there are more cars on the road and they are all "IN THE ROAD". Bikes are usually on a shoulder when available but do ride directly on the road on occasion when they have no choice.

Just the other day I was approaching an intersection on a gloomy overcast day. I had my 80 lumen front blinkie on and flashing on my handlebars. I also had/have a torch ( XP-L LED ) set for fast flash that I have on standby sitting on my helmet. My main front lamp was not on. As I approached the intersection I slowed, reached up to turn on the torch ( no shoulder on this road ) and slow rolled toward the cars that were already at the light. No cars were in my lane in front of me. Just before I got to the white line the light turned green and I started through the intersection. When I entered the intersection I noticed that a car on the opposite side of the road was already in the intersection trying to make a left in front of the on-coming traffic. I think I saw him the same time he saw me. Both of us came to a stop. Did the high power flash of my torch being aimed right at him make him stop? I have no idea. I just know that if someone aimed a high power flashing torch directly at me that there's probably a good 95% chance that I'm going to see it as long as I'm looking where I'm driving. I'm just glad I didn't get mowed down. Why didn't the guy see me sooner?...maybe because I slow rolled up to the light and was blocked from his view by the other traffic beside me (?). Nope, lights won't prevent all accidents but given the right circumstance/situation they can help the cyclist get seen and getting seen ( sooner rather than later ) is the first step in preventing accidents.