Since there is an inverse square law at work here, and no industry standard for reporting the useful output of bicycle lamps (say lux at x meters distant, y meters wide, one meter high, overspill ignored), you're stuck in these comparisons until some reliable party offers side by side comparisons, and even then it is usually more persuasive to listen to the reasons behind the reviewer's own choice than to look at the photographs. The photographs are good for reporting the negatives, like hotspots and a beam shape for blinding pilots and a lack of side throw that is important in narrow ways, but not for telling much about the quality of the light (except the beam shape) because you're looking at ideal conditions which you will never meet riding.
I think it is far more useful in choosing among the IQ BUMM lamps, and near competitors like the Herrmans, to give a pretty high value to reporting by actual longterm users whose bicycling purposes and circumstances are near yours. In addition, there may be practical functional differences, for instance the BUMM lamps, even the most expensive, are notoriously not waterproof, or even well protected against water, from below; is the Herrmans waterproof? Another instance: BUMM IQ lamps are widely praised for the top cutoff, which is said not to irritate oncoming motorists; well, the hell with oncoming motorists: on my bike I'm taller than a Range Rover and I ride in Irish lanes where I want low-flying branches as thick as my arm to be lit up before they hit me in the face, and I want to see high roadsigns warning of country crossroads before a truck barrelling across the junction hits me.
I have formed a subjective opinion that the Luxos has been reported broken too often for comfort and, even though I could use the USB output, have thus not replaced my trusty first series Cyo with a Luxos despite the fact that I have no bikes without mudguards and my bikes all have stands and thus the lamps are not unduly exposed to wet.
Herrmans, by the way, is considered by the German baukasten (custom houses) to be a high-class purveyor of excellent, good-value bike components. My Utopia, for instance, came with the standard fitting of Herrmans grips, and very agreeable they were too.
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Even if the Herrmans and BUMM lamps were measured under exactly the same conditions with the same parameters, there will be no practically observable difference between 100 and 90 lux discernible with your bare eye. You can therefore choose according to other parameters important to you without later regretting the decision.
