I've already got a Lezyne Femto front light for emergency to be seen by, but want something I could continue riding with.
...
" it's a long wait until dawn if you do have a failure" - well put, that's my thinking - to enable me to continue, if necessary at a slightly reduced pace.
I had a dynamo fail on me at the weekend on a 300. I always have a Femto rear light to give a gentle blink (they're not very bright) to remind cars behind that the big dynamo rear does not mean "motorbike". But I added a Femto front as I passed Evans in Norwich.
It was a half-moon night, so about 5% sunlight reflected, and another 5% from the Femto meant I could see where the edges and centre of the road were, and I could tell where most pot holes were, too.
I had a helmet light, but I knew that wouldn't last the five hours to home, so I used that only when absolutely necessary, like under trees.
It's a funny thing — we've become sooo used to having bright, bright lights on our bikes these days that we've forgotten what it used to be like. The Femto + moon were just bright enough to guide the bike steadily home, and the helmet light really helped in the dark bits. Reflective gilet and shoes meant I still looked like a cyclist.
Ironically, I had removed a spare helmet light from my Carradice the weekend before for a 200 completed in daylight. If I had had the spare with me then I would have had just enough between the two to not require the Femto, and I also carry the little velcro strap specifically so that I can attach it to the bars to be legal (as legal as any battery lights in the UK at the moment, anyway), i.e. my helmet lights are my backup lights.
I got home fine.
Several lessons learnt, but the most useful being that when you don't have much choice then you really can get away with very little light and still be okay.