Motorcycles didn't always have lights. They have them now and they run them day and night. When someone is looking ahead in traffic they are looking for things that can interfere with there travel. They easily Se larger objects like cars and trucks. This is what they expect to see and there brains are accustomed to this. Motorcycles, bicyclists and pedestrians are often missed when they are scanning the road. What gets people's attention, when they are driving there automobiles, is bright lights and movement. Noise can also work if the motorists is not playing there radio to loud and the emergency vehicle is close enough. There have been plenty of studies on this to prove lights are effective. When I started bicycling in the mid seventies I rarely had close calls with motorists passing to close. It has become all to common since then. I purchased my first tail flasher near 7 years ago. It had an immediate effect. Some People have better things to do while driving than drive. You can't always watch your back. Lights help with this problem.