Two major scientific research studies into the causes of motorcycle accidents have been conducted in North America and Europe: the Hurt Report and the MAIDS report.
Hurt Report (Extract)
The failure of motorists to detect and recognize motorcycles in traffic is the predominating cause of motorcycle accidents... Conspicuty of the motorcycle is a critical factor in the multiple vehicle accidents, and accident involvement is significantly reduced by the use of motorcycle headlamps-on In daylight."
A New Zealand study supported the Hurt Report's call for increased rider conspicuity, daytime headlights may reduce motorcycle injuries and death. The study found that riding with headlights on reduced the risk of a crash injury by 27%.
On most new motorcycles in USA, the headlights turn on as soon as the bike is started as a legal requirement.