Thinking Outside The Box

On 3/12/2012 8:32 PM, Sepp Ruf wrote:
Peter Cole wrote:
On 3/12/2012 2:59 AM, Sepp Ruf wrote:
Peter Cole wrote:

I think that's what I said. You can can convert lumens to candelas if
you know the beam angle (and it is uniform), from there, you need to
know the target area and distance to compute the illuminance in lux.

Sure. However, at least in the small world beyond toy manufacturing,
passing beams are not at all uniformly angled, and the relation between
source lumens, and a bunch of target illuminances at specified beam
angles is more complicated.

Sure, but if you specify the candelas in a diagram with isometric
contours, by angle, as is commonly done, then distance doesn't enter
into it. Giving the light output in lumens doesn't tell you anything
about beam pattern or incident illumination, but it gives you a rough
comparison.


I struggled through what might have been a poor translation. As I recall
10 lux was the minimum for illuminance of the target area. That seems
dim for "seeing", more adequate for "being seen".

The tarmac at 10 meters' distance is sort of immobile, and not
interested in "seeing" you. One needs to consider the differing angular
intra-beam differences between "seeing" and "being seen" parts in a
passing beam.

I understand, but that doesn't answer the question of whether 10 lux is
adequate, or if 2 lux (or whatever it is) is overly strict.


But here's news, or quite the contrary: The vertical "being seen"
minimum above cut-off is not defined anywhere in the German bicycle
lighting standard. Some disinfo "experts" will never, ever, grasp this,
of course.

I thought the maximum was, I could understand having no minimum value,
but that's not particularly relevant.


From
http://swhs.home.xs4all.nl/fiets/tes.../index_en.html

Well, the guy is really good at boosting Philips LED lamps, recording
his rides, putting up a website, and all that, but he tends to jump to
conclusions rather quickly.

"studying the StVZO requirements for car and motorcycle headlamps, it
all becomes clear.

Bicycle headlamps may only put out a light density of 2.0 lux above 3.4
° above the brightest spot in the beam.

"light density" - not.

Not a technically accurate term, but reasonably expressive of the principle.


With cars and motorcycles, the
measurement is not at 10m, but at 25 m, and their lamps are allowed to
be 1.0 lux maximum above the cutoff. Well, this means cars can blind
oncoming traffic with a light density at 10m of 2.52 x 1.0 lux = 6.25
lux!

Seems like he didn't look up the "car" standards that tend to be a bit
more complicated, even above cutoff. And maybe he missed that cars tend
to employ two of these lamps - which might have helped his argument.

So, all that aside, does he have a point?


This is more than 3 times what bicycle lamps may put out in that
region! (actually, what they are probably supposed to put out at maximum
there, see the section StVZO's requirement about how bicycle headlamps
should be aimed)

questionable logic, maybe a language problem. As mentioned above, in
German bicyle lamp standards, there is no minimum anything above cutoff.

No, but there is a maximum, which I think is the point.


Also note that bicycle lamps are since several years in
StVZO required to be at least 10 lux.

20 lux for higher rated source flux levels

I don't follow.


This is the intensity of the beam
measured at 10 m, not the intensity of what the cyclist will see from
what's reflected back to him! So it's clear why a halogen lamp that puts
out 10 lux at 10 m on a wall is useless to see the road on parallel
roads, because you're going to get far less than 10 lux back to your
eyes, and yet you're getting up to 6.25 lux into your eyes from car
lamps.

overly simmplifying the visual process; not employing real-life glare
illuminances at eye level. Okay, he also rides an incumbent, and thus
is prone to getting hit by much more than 6 lux.

Why are the rules so much less strict for cars? (again, when assuming
the rules for bicycles were meant to allow only 2.0 lux or less above
the horizon, not when taking what they really imply, see the section
StVZO's requirement about how bicycle headlamps should be aimed) And did
the StVZO people really expect cyclists to see anything on parallel
roads?

ranting.

Do the StVZO people actually ride bicycles?

As far as I know, some of them once tried, but somehow, the whole thing
didn't quite work out. Might have been the mandatory helmet law that
backfired:
https://upload.wikimedia.org/wikiped...fahrtruppe.jpg

On 3/12/2012 8:48 PM, Phil W Lee wrote:
Peter considered Mon, 12 Mar 2012
14:26:42 -0400 the perfect time to write:

On 3/12/2012 5:36 AM, Phil W Lee wrote:

The German standard is also successful, in that the rate of night
collisions between cycles and motor vehicles is very low.
Presumably you prefer to operate within a system that accepts a far
higher level of cycle/motor vehicle collisions?

Do you have any data on the comparative differences in MV-bike
collisions for US, UK, DE, NL, night vs day? I haven't seen any.

I've seen them, but don't have a copy or link.
One of the strange facts I noticed is that in the UK, unlit cyclists
apparently have a lower collision rate than legally sit ones, which
seems to imply that the British standard does more to inspire
confidence than confer visibility.
The UK also has one of the worst rates in the EU for MV-cycle
collisions (all times of day), which isn't very inspiring.
One thing that I suspect may be a factor (although I've never seen
data to confirm or confound my suspicion) is the lack of enforcement
of motor vehicle lighting standards in the UK - it's far too common to
see motor vehicles with misaligned headlights, abuse of foglights or
main-beams, which dazzle other road users, and would render a cyclist
invisible. That may make more difference than cycle lighting itself
does.

I'm sure it's even worse in the US, where after-market illegal mods are
all the rage. Which is kind of the reason to argue that the German 1 lux
above cutoff standard for bikes is too strict for conspicuity sake.

When I look at my typical 3W, ~200 lm LED lights, and see the typical
"spot + spill" beam pattern, and the spill area is over 1m square at 1m
distance, means I've got ~2 lux at 10m if the beam was uniform, which it
isn't, the spot being much brighter, probably has less than 1 lux in the
spill. Even my new 500 lm light probably has less than 2 lux in the
spill, which is the limit for German cars, I've been told. That doesn't
seem all that excessive, particularly when some motorists are running
2x3,000 lm around here. I find the 500 lm light to be decent, the 200 lm
light to be barely adequate for seeing. As for being seen/dazzling, I
find the claims to be a little overstated, provided you can keep the
spot out of oncoming eyes (other than when you deliberately use it to
warn), something that's not to difficult with proper aiming.

On 3/12/2012 9:12 PM, James wrote:
On 13/03/12 10:44, Peter Cole wrote:

The beam shape is conical, the intensity is what it is, but the
efficiency usually isn't state of the art, they're not all that cheap
(compared to other power LED devices), they're much larger than they
need to be, mounting is problematic and they're not weather tight
generally.


Another reason I don't like the idea of electronics on a bike. The
record to date is that lights are generally poorly sealed. My headlight,
which is 4 CREE LEDs with lenses arranged as a full bridge rectifier,
uses no weather protection at all. It may corrode in a heavy salt
environment, granted, but I can spray water on it all day and it
continues to work just fine. Interconnecting wires are 1mm enamel coated.


I dropped one of my battery powered LED lights off the boat one night in
about 10 feet of salt water. It was cheerfully shining on the bottom as
I sadly rowed away.

The deal for water proofing lights is mostly to keep the reflectors &
lenses from fogging. I had another LED light that didn't react well to
being soaked with brake fluid -- the lens got distorted. LED lights
aren't nearly as delicate as cell phones.

On 3/13/2012 12:06 PM, Peter Cole wrote:

When I look at my typical 3W, ~200 lm LED lights, and see the typical
"spot + spill" beam pattern, and the spill area is over 1m square at 1m
distance, means I've got ~2 lux at 10m if the beam was uniform, which it
isn't, the spot being much brighter, probably has less than 1 lux in the
spill. Even my new 500 lm light probably has less than 2 lux in the
spill, which is the limit for German cars, I've been told. That doesn't
seem all that excessive, particularly when some motorists are running
2x3,000 lm around here. I find the 500 lm light to be decent, the 200 lm
light to be barely adequate for seeing. As for being seen/dazzling, I
find the claims to be a little overstated, provided you can keep the
spot out of oncoming eyes (other than when you deliberately use it to
warn), something that's not to difficult with proper aiming.

There are numerous sites that compare the illumination of different
lights. The Magicshine is about the best in terms of the beam pattern
because it illuminates not just directly in front of the bicycle, but
sufficiently off to the sides but at a lower intensity so you're not
blinding on-coming traffic.

It'd be interesting to see the beam patterns of the Magicshine clones
like the one you bought. It's rather ironic that some of the older
bicycle lights with their attempts at beam shaping end up being far
worse for cycling than a symmetrical beam.

On 3/12/2012 9:18 PM, sms88 wrote:


On 3/12/2012 4:44 PM, Peter Cole wrote:
On 3/12/2012 3:43 PM, SMS wrote:
On 3/12/2012 9:01 AM, Jeff Liebermann wrote:

Ok, I'll concede the point. With a generator, which acts as its own
voltage and current regulator, a PWM regulator is not necessary.

Actually the dynamo voltage continues to go up with increased speed.
That's why with the older incandescent bulbs you needed a protection
circuit to prevent burning the bulbs out.

Depends on the load. Incandescent filaments increase resistance with
current, so you basically get thermal runaway.

Yes, what I was referring to was the older incandescent bulbs which were
a resistive load. With LEDs (diodes) once they are forward biased the
current flows through and the voltage is determined by the voltage drop
across the diode(s). That's why you often see multiple LEDs in series or
in series/parallel, to raise the forward voltage to something more
practical for the battery voltage.

The beam shape is conical, the intensity is what it is, but the
efficiency usually isn't state of the art, they're not all that cheap
(compared to other power LED devices), they're much larger than they
need to be, mounting is problematic and they're not weather tight
generally.

Quite weather tight actually. The size has an advantage because of the
larger reflector (or multiple micro-reflectors). Mounting is indeed an
issue. Not difficult to overcome fortunately, and once you do fabricate
an appropriate mount it's much more secure and better protected than the
typical mass market plastic light.

I hear you, but my days of hacking LED lights may be over. I mounted one
(3W MR-16) on a gooseneck to use as a reading light. It came out very
slick indeed, but I spent one whole frickin' day on it. Not efficient,
not when I can get the whole shebang (bike light) for under $40. I'd
wire my dynamo to a Lion charger and be done with it, even if I had to
breadboard the electronics. Anything beats metal work.

On 3/12/2012 9:58 PM, Jeff Liebermann wrote:
On Mon, 12 Mar 2012 15:18:40 -0400, Peter Cole
wrote:

Still all sounds complicated. When will you be joining the electronic
gear shifting crew?

http://en.wikipedia.org/wiki/Electronic_gear-shifting_system

"Electronic_gear-shifting_system" Er, that's an electro-mechanical gear
shifting system. Big difference.

Is there some some technology that I've missed which shifts gears
without doing anything mechanical?

No, that was my point.

On 3/13/2012 3:24 PM, sms88 wrote:
On 3/13/2012 12:06 PM, Peter Cole wrote:

When I look at my typical 3W, ~200 lm LED lights, and see the typical
"spot + spill" beam pattern, and the spill area is over 1m square at 1m
distance, means I've got ~2 lux at 10m if the beam was uniform, which it
isn't, the spot being much brighter, probably has less than 1 lux in the
spill. Even my new 500 lm light probably has less than 2 lux in the
spill, which is the limit for German cars, I've been told. That doesn't
seem all that excessive, particularly when some motorists are running
2x3,000 lm around here. I find the 500 lm light to be decent, the 200 lm
light to be barely adequate for seeing. As for being seen/dazzling, I
find the claims to be a little overstated, provided you can keep the
spot out of oncoming eyes (other than when you deliberately use it to
warn), something that's not to difficult with proper aiming.

There are numerous sites that compare the illumination of different
lights. The Magicshine is about the best in terms of the beam pattern
because it illuminates not just directly in front of the bicycle, but
sufficiently off to the sides but at a lower intensity so you're not
blinding on-coming traffic.

It'd be interesting to see the beam patterns of the Magicshine clones
like the one you bought. It's rather ironic that some of the older
bicycle lights with their attempts at beam shaping end up being far
worse for cycling than a symmetrical beam.

I think the "spot & spill" is pretty common with the cheap power LED
lights. The LED devices typically have a molded lens, which provides a
"Gaussian" beam (the spec sheet usually has profile). When you add that
to a parabolic reflector, you get a spot from the parabola, except for
the light from the LED lens which doesn't hit the reflector, which gives
you the spill (at least that's how the ray tracing looks to me). So it's
a combination of the size and shape of the LED integral lens and the
reflector. Some reflectors are textured, mine aren't. The cylindrical
lens I put on it spreads the beam in the horizontal direction by about a
factor of 4, which seems about right. At perhaps 10-15m distance, the
spot spreads to street (narrow residential) width, the spot seems to be
about 10 degrees by 40 degrees.

Many of the reviewers of the particular light I bought said they found
the beam too narrow. I can believe that, but the spreader made a
substantial difference. The spot is pretty artifact free, while the
spill has slight vertical bars from the cylindrical lenses. I don't
think it will suffer from the "tunnel vision" effect, nor do I think it
will be irritating, provided I keep the spot out of other's eyes, which
is pretty easy with a head mount, the acid test being when you encounter
another person on a 4' bike path.

On 14/03/12 01:30, Jay Beattie wrote:
On Mar 12, 7:35 pm, wrote:
On 13/03/12 12:55, Dan O wrote:
snip

Mostly because it adds weight that I do not need to have, and it costs
me a minute to remove. I would remove a battery powered light for the
same reason. Our racing club now mandates rear red blinkies for winter
road races, so not all lights come off.

Mandates blinkies for road races? Why? A road race in daylight is
pretty unmistakable to traffic, particularly with all the brightly
colored riders, follow cars, lead cars, signs, corner marshals, etc.,
etc. Spring racing in Oregon is challenging because of all the rain,
but even with getting blasted in the face with wheel spray (and
wearing glasses), I never ran in to the guy in front of me. Not that
blinkie weight is a big deal. It just seems weird to require one.

Yup, a lot of us find it a bit weird, but our club safety officer is a
little zealous about keeping us safe. Whether it helps or not is
another question. I guess in the middle of winter, the sun is quite low
by the time the race is over, and if it's overcast and raining as well,
visibility for a driver could be judged poor. A blinkie through the
raindrops should stand out better than nothing at all.

--
JS.

On 14/03/12 02:50, Sepp Ruf wrote:
James wrote:
On 13/03/12 11:12, Phil W Lee wrote:
considered Sun, 11 Mar 2012 13:28:47
-0700 (PDT) the perfect time to write:

If the Germans have outlawed the use of a flashing light on a bicycle,
I think they're backward, and I don't care how many ex-spurts I have
just disagreed with.

Accident stats seem to indicate otherwise.
Maybe you are facing the wrong way?

Haha, you're funny.

I seem to notice flashing lights on bicycles from a long way away, that
I think would otherwise be lost in the noise.

Authorities and advocates here recommend flashing lights.

Ohhhh, "authorities" and "advocates" - and who's that, exactly? Where
were their methods and findings published?

I interpret your tone as you have bee in your bonnet.

http://www.bicyclensw.org.au/files/u...Queensland.pdf


"Flashing tail-lights are highly effective. Observers have
difficulty in seeing bicycle headlights, partly because they had
difficulty in identifying them as
bicycle lights."

So you copied from the summary, great. Where are the facts?

A wasp in your bonnet, perhaps?

Where can we look up the demonstration of a necessity to identify
bicycle lights as pedal-bicycle lights, as opposed to being mis-
identified as motored-two wheeler lights?

To which straw man are you addressing that question?

Since that document was released, this has become part of the law, and
not just a recommendation.

Thanks a lot for the crappy user survey, here's a link:
http://www.austlii.edu.au/au/legis/v...9208/s259.html

That says the same thing. You're not doing well, are you?

"a flashing or steady white light (arguably then, the blue lights which
are becoming more popular as front lights offend this rule) that is
clearly visible for at least 200 metres from the front of the bicycle;
and
a flashing or steady red light and reflector that is clearly visible for
at least 200 metres from the rear of the bicycle; and"

So they got around implementing vehicular-type norms, instead using
late-19th century categories such as "clearly visible for x metres."
Where is the Australian Plastic Toy Importers' and Manufacturers'
Association supposed to send the cheque to?

Boy, you really got out of the wrong side of bed, didn't you?

Is the flash cycle specified anywhere? Otherwise, bad luck if the
off-period of the flashing cycle happens to coincide with with a
driver's gaze duration.

Your first serious question. Well done.

The answer is, not that I have found. And yes, I agree, an extra
ordinarily long off time between flashes may be a concern. I have
noticed one or two headlights that could be considered, IMO, to have too
long off time. But I guess it's up to the law makers to rule on that one.

--
JS.

On 14/03/12 03:25, Peter Cole wrote:
On 3/12/2012 11:42 PM, Ralph Barone wrote:
Peter wrote:

No, it's typically a switching regulator, which modulates duty cycle,
AKA PWM.

The use of a switching regulator does not necessarily result in the LED
being switched ON and OFF at a high rate.

I think it does, by definition.


I haven't analyzed any, so I
can't comment on how many bike light current regulators PWM the LED,
versus
more sophisticated control methods.

As an EE, I can't think of any more "sophisticated" method, unless
you're modulating it to send data or something. FWIW, I've designed a
few PWM circuits for lamp (arc) control, a few switching power supply
regulators and a motor controller or 2.


Then consider a constant current source implemented as a buck converter
where the inductor current doesn't fall to zero.

The average current is kept constant by PWM, and the current is never
zero. It's operating in continuous conduction mode.

--
JS.