The bigger issue isn't whether your lights are on - its whether your lights are in fact are effective.
The question every geek in this forum should be asking is: What does a driver make of me from a 100 meters back?
After riding for my entire life - and this is not so much a boast - as much a fact - I've ridden over 200,000 miles and I never realized that I would be could be struck by an automobile in the afternoon's day bright sun light.
In my case I was hit by a driver looking "right through me" - and watching for other automobile traffic.
So as far as posing questions about a tail light somehow being a big part of your safety - remember a very important contribution to your safety comes from a continuous vigilance regarding not just your visibility - but all the elements that contribute to your situation. Among them , the choice of your route, and your ability to avoid a collision or contact with an automobile up to the last possible second.
Don't let a working tail light lull you into paying less attention.