Originally Posted by
bhdavis1978
[...]I.e it’s dark out. On top of that the start of my ride proceeds through rural roads or along major highways without lights. Consequently I am a little bit obsessed with bike lights and bike tech in general.
[....]
But I am getting tired of always charging batteries. I want to get a dynamo light. The thing is, there is very little information around comparing the relative brightness and utility of battery powered lights (measured in lumens) and dynamo lights (measured in lux). I understand the technical reasons for it. The dynamo lights use mirrors and lenses to focus the light where you need it, instead of blasting it everywhere like most battery lights. But as a consumer that doesn’t help me figure out if the dynamo light will meet my needs.
If you are tired of charging batteries, maybe take a look at the
pedalcell system, if you like your current lights. unfortunately those lezynes can't be charged while using. There are other bike harvesting systems for hub dynamos available as well.
Best available dynamo light: B&M IQ-X. With a hub dyno you could operate two of them in series, no issue for the hub dyno to deliver this power. Then you'll have at least 500 lm on the road....
on lux (and lux requirements) and lumens
For all those that wonder: the lux values given for dynamo lights are due to the (german...) road traffic authorization regulations (StVZO), which have very strict rules on bicycle lighting. (i.e. a car headlight is allowed to be three times as bright above the cutoff than a bike light....). For any driving/dipped beam, the beam pattern is defined in spots on a vertical screen 10 (bike) or 25m (car) distance from the light. So for bike lights, the brightest spot is given in lux, and that brightest spot has to be just under the cut-off line.
Here are those measurement points (HV: horizontal/Vertical crossing= brightest point, O= above/upper L=lower) (sorry in german, i don't know any english source with that information). So this minimal requirements from the StVZO are pretty low and only a very tiny area (~0.4 mē) on that screen has to be at least half as bright as the max brightness (in lux), the other points are just minium requirements (above 2 lux, moonlight is ~0,5lux...).
tldr: those single point lux numbers don't help much, unless you compare a bunch of lights at the same spot, with the same camera settings and you ideally compare wall shots of those lights as well. e.g.
here (PDF, see page 6 (51); sorry german again...)
The lumens on the other side don't help much either, since the don't tell you where the light goes. A good 500 lm from a B&M Ixon Space (150 lux) is equivalent in beam distance and width to a >1500 lm conical beam...
Examples:
1.
Here is a wallshot of a 40 lux StVZO approved light (
here on a bikeway), and here is a
wallshot of a 150 lux StVZO approved light (and here the
same light on a bike path). Both wall shots seem to be taken roughly from the same distance (don't know whether camera settings were identical, but just look at the vast differences in beam width, a information which is not given by lux value or StVZO certification, as this gives you only throw in a tiny area...)
2.
500 lm/150 lux cut-off beam (supernova m99 mini pro 25) vs
1800 lm conical beam (Lupine Blika), both pictures taken with identical camera settings, the third marking is at ~60 m
Originally Posted by
Koyote
How did you shoot the photos? Unless you used a camera set manually to the same exposure value for each set of comparison shots, the camera’s autoexposure will render the comparisons meaningless.
True true..
edited, took out DrIsotopes quote, it is discussed anyway in the next post