One thing I have only recently noticed is that lights can be a very good idea on rural roads. In the Summer there can be a large change in ambient light between full sun and the deep shade of mature trees over a low traffic road. Without a light, a cyclist in the shade can be nearly invisible to a motorist in the full sun, and, of course, the lightly travelled road is just where the motorist is expecting little or no other traffic. Paradoxically, a bright, clear day makes it hard to see a cyclist.