Originally Posted by
noglider
I agree with the principal of backup lights, but I'm curious. Have you ever had to bring in a battery light because a dynamo light has failed? I haven't, not once. I have had plenty of battery lights drain or fall off the mounts and fail in other ways that having backup would have been a good thing.
Once I noticed my dynamo tail light wasn't working. One of the wires had fallen out of the light. That's the only failure I have had.
I've only needed it as "backup" on classic bikes with vitage incandescent bulb dyno lights as a stand light, or when a bulb went out.
They're also useful to supplement functioning dyno lights with the flashing function in certain low visibility conditions.
I did have a bearing in a Sanyo hub go bad, ruining the hub, but I don't count that as a lighting failure per se.