On my hybrid I use two lights up front, the second light isn't necessarily a spare but could be I guess, for day time riding I have the Bontrager Ion 100R in service and at night I switch to my Bontrager Ion 800R......my road bike has just one light up front, the Bontrager 100R, I rarely ride this bike at night but on occasion my ride time has extended into darker hours and the 100R has performed the task.