What a joy to live in a time when we can debate the 'best' bicycle lights. For most of the last 140 years, lights for cycling were abysmal, and any debate would have been about which light was least worst. A look at the illustrations of Daniel Rebour is 'illuminating':
tiny generators,
strap on flashlights!
Your "refined" optics for generator lights are a relatively recent development. Not too long ago (less than 15 years), the Union headlamp was the light to use for generators. It was a simple round parabolic reflector that was as sophisticated as 1965 Chevrolet Impala headlamp.
The Union 100 actually had a pretty good lens that herded up its feeble collection of photons and threw a usefully shaped beam.
My favorite optics from the bad old days, though, was the BEREC Ever Ready Frontguard II, with its lens designed by the Department of Opthalmic Optics at London University.
"
We feel it is quite the best lamp on the market.' - International Cycling Guide, 1982.
Can you imagine: a headlamp with a 3W filament bulb and twin D-cells being the best on the market? How did we survive?