incredulous wrote:
No, motorcycles, scooters, ebikes, bikes, pedestrians and trikes all have
in common small apparent object sizes compared to automobiles and trucks.
I’m not current on effective conspicuity research. On crash research, I
respect, FK, that you refer to it, but as someone who did road safety
research in the past, I’m aware of challenging differential selection
problems, much greater now that ER care is so damned expensive.

Getting back to Subject, I doubt that steady DRLs of either kind do much
good for bicyclists.

It depends on the traffic and visual environment. Much of any conspicuity
effect possibly attributable to a bicycle DRL is already being taken care of
by sensor-switched bicycle lamps that, unless aimed too low, do a sufficient
job of marking the vehicle's front in dawn, dusk, and tree/forest
situations, when uneducated or unsuspecting riders are not aware they can
see much clearer than a windshield-impaired cager or a vizor wearer.

It may be worth pointing out for young ones that for
motorcycles, running lights were for use in German cities at night
instead of headlights in an era before motorcycles or scooters had turn
signals which could be steadily lit as Americans called ‘parking lights.’
My BMW R26 had a small 5w bulb in the bottom of and illuminating the
175mm headlight cone.

Checking (then contemporary) StVO paragraph 23, I doubt these were
officially meant for anything other than standlights / position / parking
lights in stationary use due to lack of generator power / battery capacity.
Driving with just position lights illuminated has been illegal in Europe for
quite a while, though it might still rarely get ticketed.

The position light regulation applied in recent decades would be UNECE
Regulation #7, stipulating a 4cd minimum (sic! -- and a 140cd maximum)
on-axis intensity. Whereas DRL intensity in UNECE DRL Regulation #87 is
400..1500cd or so on axis, and commonly higher luminance than a traditional
5W, 50lm position light's incandescent bulb mildly glowing away behind
scattering optics.

So, without looking up 1950's technical by-regulations, I'd assume the
domestic-market BMW R26's position light was not putting out close to 140cd
into most angles, twice the bicycle-specific 70cd glare-zone maximum
permittable in outdated former versions of StVZO (now 200cd) and ISO.

IOW they were the functional equivalent of what marketers of low light
output bicycle lamps sell for lit urban streets at night, ‘to-be-seen
lights’.

In 2019, are 5cd to-be-seen lights selling well? Maybe online ... when
labeled "5,000,000 µcd LED!"