I told the author of this Outside Online article that this issue is a double-edged sword and we want to be careful about imposing even more non-law-required "requirements" on cyclists. Is riding with a light during the day time a good idea and does it help if you are hit from behind in your case against the motorist's insurance company? Sure. But do we want this to work against cyclists who choose NOT to use day time lights? No, we do not. We don't ask motorists to drive their cars with daylights running, so let's be careful insisting that cyclists must.
The law requires us to ride with lights on the bike from 30min before dusk through 30min after sunrise. There is no law that requires daytime lights. This is up to the discretion of each individual rider.
"“Anytime a cyclist can say they were doing everything right, such as riding in a bike lane, wearing bright colored clothing, bright helmet, reflective gear, it decreases the chances of blame or fault being apportioned to the rider,” says Megan Hottman, a Golden, Colorado-based attorney specializing in cyclists’ rights through her company TheCyclist-Lawyer.com. “So the addition of blinking lights in the daytime helps bolster the case for the cyclist.” Hottman cautions that daytime lights won’t determine the outcome of any case, but they could help. "
Complete article here.