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Note: I get questions from time to time about acquiring StVZO in English, well, it's only published in German (you can buy it here: Kirschbaum Verlag, StVZO), if you want it in English you need to get it translated (which is a lot of work), and then you need to interpret the rules which are unclearly written, even sometimes contradictory, and incomplete (not including some rules that have been made), and containing old rules that should have been taken out (but haven't because nobody bothered to sort it out and publish it in 'Verkehrsblatt'). I can do this, of StVZO (traffic rules for end users but also some stuff of important for manufacturers and dealers), TA (rules for the design/build of bicycle lamps/dynamos), FzTV (rules for the approval process, samples to be provided, production checks, etc.) and more. Email if you are interested. But note that the approval process also takes time and money, I heard that that costs about €2500,- and takes at least 3 months, for example. These issues of the rules and the approval process and costs for those, may be one reason why there are not that many manufacturers making StVZO approved headlamps/taillamps.
I have StVZO updated to 2015-4-1 + fixes from other sources. The changes since the first version that I got hold of (2010-9-2) are slight, and don't influence the analysis here.
In the updates up to 2015-4-1 not much has changed since 2010, really just small stuff in StVZO.§67 and not all of it was strangely in StVZO itself as published by Kirschbaum, but an addendum that I got from another source. Also, as to deviating from the rules and/or rule changes, I heard in 2014 that 1.5W dynamos were really allowed, but it was unclear how. It is not in the StVZO/TA rules and later it became clear that it was done via an exception in StVZO/TA, to allow other rules. In this case it is StVZO + DIN33958. There are as of end of 2015 a few new lamps for such low power dynamos (at least, low power at low speed, the Velogical dynamos for example are high power at high speed!), a B&M headlamp and a new taillamp from Herrmans, the H-trace. I will check out that taillamp, but the headlamp and the whole concept of 1.5W lighting seems pointless to me. Cyclists can lose a few more Watt of power to lights, this is not a problem!
StVZO is the German rulebook for vehicles on the road, including bicycles. TA (Technische Anforderungen) is the more precise set of rules and descriptions of testing methods used. Apparently StVZO will eventually be split up further (such as has been done with some sections already), but I'm describing the current rules that will probably be of large influence what will be in later versions whatever they may be called, even though they may be changed due to European harmonisation.
The problem with StVZO, apart from needing a lot of time to decode it, the bad numbering system which makes you wonder if something is a section, paragraph or list element, the language which is bureaucratic which means you need time to get used to it (and until that time you will also be wondering about the strange or unfamiliar use of words, for example the 'lichtmaschine' which literally translated is a 'light machine', but which is the power generator, i.e. the dynamo or dynamo hub) is that there are too many bad rules. The power requirements for example are in a sense pointless (I have elaborated on this further on): there should only be light brightness requirements, both minimum, to ensure reasonable illumination of the road, and maximum, above the cutoff, to prevent blinding oncoming trafffic, and some way to guarantee a headlamp + taillamp working with approved dynamos (this latter fact of guaranteeing that components work with each other is I think a large part of the reason of the power requirements for headlamps (and to a lesser degree taillamps) in StVZO/TA, but as I will describe, that choice could have been made differently).
The most important parts of StVZO and TA for bicycles:
LED lamps are apparently not a "bauartgenehmigte" light source (bauartgenehmigt = approved for the given use), and for such lamps the rule is the light source must be fixed in the headlamp. The requirements then go on to say for such lamps with 'non-replaceable' bulbs, that they must be 2.4 W for 6V, or 5.0 W for 12V/13.5V (both within a range of 0.80 x to 1.10 x (-20% to +10%), so for 6V a LED headlamp can be 1.92 W - 2.64 W, and for 12V a headlamp can be 4.00 W - 5.50 W.
But aren't all dynamo systems 6V you may then ask? Well, a dynamo is usually nearly a current source with variable voltage. There were and are some different dynamos not based on claw-pole design such as the Lightspin (no longer made), and the Sunup 3 phase generator. In terms of the measurement system of StVZO/TA which is done with resistors, StVZO approved dynamos are 6V systems, or more accurately, such dynamos must provide 6V at 3W when using resistors of 15Ω (headlamp, 2.4W, 6V at 0.4A; R=U/I=6/0.4=15Ω) and 60 Ω (taillamp, i.e. 0.6W, 6V at 0.1A) parallel, or a total resistance of 12 Ω (3W, 6V at 0.5A) when riding at 15 km/h. However, there's a rule that the 'light machine' (= the dynamo/generaot) must be at least 3W, with a nominal voltage of 6V. It also says that lamps can have suitable electronics to change the voltage to requirements... Can you guess now what this means in terms of what's possible? Of course, perhaps I've made a mistake in deciphering (and that's really what it is!) StVZO/TA.
All right. As you can find out elsewhere (esp. on the forum of mtbr.com and candlepower forums, see esp. the postings by Ktronik, e.g. candlepowerforums.com: Dyno-powered-triple-cutter-R2 and candlepowerforums.com: 3-Cree-R2-dyno-light-circuit-re-drawn-for-newbies), with suitable use of capacitors it's possible to coax more than 0.5 or even 0.6 A from in particular a dynamo hub. Even more than 0.70 A... (but not over the entire range of speeds when cycling) Using a current doubler and a single LED it should then be possible to drive the LED at more than 1.23A assuming a Vf (voltage at which the LED fully lights) of 3.25V, i.e. more than 4.0 W. Then say the headlamp is a 12V lamp, include the 'Vorschalt Elektronik' (adapting electronics) to use it on a 6V dynamo hub. This 'Vorschalt Elektronik' is actually not needed (i.e. a null circuit), as long as you make sure the lamp's electronics will work ok on a 12V source as per the TA measurement method. I think this will work, if the TA measurement method for the headlamp uses a power source similar to a dynamo hub. This is apparently so from a brief read in the various sections but I'll have to check some more.
Note: A just introduced StVZO compliant headlamp from Supernova (early September 2010 it was listed on their website but it will probably not actually be available until some while later) claims 305 lumen from a Cree XP-E R3 which can only be done at more than 1.15 A (note that the light output is obviously not measured but a datasheet value which is sometimes overly optimistic by Cree; this is so esp. for the XP-G, see http://www.mtb-news.de/forum/showpost.php?p=6895756&postcount=1089 where the XP-G R5 is measured at 275 lumen instead of 350 that Cree claims in their datasheet, and the XP-G R4 was measured a while before that, which was similary below the datasheet value). This means the LED gets more than 3.74 W (assuming a Vf of ca. 3.25V) which is very close to 4 W, and including losses in the electronics this means it almost certainly uses more than 4 W (or is only the power through the 'bulb', i.e. the LED in this case, of importance in the StVZO determination? I'll have to reread the text). I think this lamp was approved using the same idea as mine above, i.e. to say it's a 12V lamp and let it be tested as such.
Alternative explanation (added 4 December 2010): perhaps it's just a 2.4W lamp and they're producing fairy tales. Note that the latest E3 pro was measured at just 140 lumen at 20 km/h (http://www.enhydralutris.de: E3 pro (in German)), so I'm estimating it will never get above say 240 lm maximum even at high speed, also the E3 triple which they're advertising at 800 lumen was measured at just ca. 330 lumen at 30 km/h and 345 lumen at 40 km/h (http://www.enhydralutris.de: E3 triple (in German)).
Update: I was right with my latter idea: Supernova produced fairy tales again. See below for more.
Here's a bit on what I'd like to see in a LED driver for use with dynamo:
As LEDs have been getting more powerful and more efficient at high current, soon 1 or 2 LEDs will be enough for road use, enough in the sense that more light will probably be overkill (running 2 x XM-L LEDs at 1.0A should give about 700 lumen, 2.5 times what the Philips LED bike light produces). Note that on www.pilom.de you can find with a standard circuit you can extract about 7 W from a dynamo when using 4 LEDs in series (current ca. 0.55A). With 2 LEDs this method will only give about 3.5 W. What would be needed to extract the same power from the dynamo but using 2 LEDs? Well, a current doubler. Transform the input voltage and current from the dynamo as follows: Halve the voltage, double the current, this will give (taking into account the ca. 10% losses in the regulator) instead of ca. 12.8 V at 0.55 A ( 4 LEDs), ca. 6.4 V at 1.00 A, i.e. it would be possible to drive the Philips LED bike light using a dynamo, at even higher power than when it's running from the batteries!
This could be done for speeds more than 20 km/h using a general purpose driver such as the b2flex, which will regulate the current as long as there's enough power coming in (at high enough voltage). The problem is low speeds. At 20 km/h and more this should work as the 7 W output with 4 LEDs is reached from that speed on. But lower and the voltage will drop, and the driver will go into direct drive, but this means the current will go down to what the dynamo can supply (ca. 0.5 - 0.6 A), which means the voltage will rise and go above where the driver starts regulating again, so it will oscillate between direct drive and trying to drive the LEDs at 1 A (assuming the LED drive current has been set to 1A in the b2flex). For even lower speeds the driver will stay in direct drive so if the driver can handle direct drive for a long time that's no problem. Will the mid-speed oscillation be a problem? (For the driver or that you will get flickering light) I'm not sure, I haven't tried it yet. Perhaps a special driver that takes this into account is needed, perhaps at low voltage it should do a current-halving to get more light at low speed? Certainly for more than 2 LEDs this would be beneficial.
There are various datasheets for driver ICs on the net suggesting how make a LED driver. I'm tempted to try this myself to make a dynamo driver, as the programming won't be a problem and cost of the ICs and the development boards is actually pretty low. If I do this I will make a separate page describing it.
(10) In den Scheinwerfern und Leuchten dürfen nur die nach ihrer Bauart dafür bestimmten Glühlampen verwendet werden
So lamps may only use light sources that belong in it (i.e. it was designed for a certain light bulb, then such a light bulb must be used again when replaced), but what about LEDs? Well, these are a 'nicht bauaurt genehmigte' light source. You can interpret the above quote as meaning that "if a lamp uses an incandescent bulb, then only those types that it was designed for may be used". This interpretation is confirmed by reading TA where the 'nicht bauaurt genehmigte' light sources (non-standardized light sources as it were) are listed as an alternative which are required to have a fixed (not easily changeable) light source, which is the LED, and these lamps are then tested as a whole for which there are also power limit rules.This rule that the light source must be fixed in the lamp is understandable as when using a different source (different LED type for example) the beam pattern on the road will change which means the beam may no longer satisfy the StVZO/TA requirements. The power limits however (2.4W/5.0W as mentioned earlier) are ludicrous. Note that incandescent bulbs used in other lamps ('bauart genehmigt') must be of certain standardized types, and such bulb types are approved separately from any lamps they may be used in.
more to be added...
StVZO or rather TA4 sets power limits for the headlamp at 2.4W (6V (effective voltage), range: -20% to +10%) or 5.0W (12V (effective voltage), range: -20% to +10%). This is a measurement done at 6Veff voltage using a power source equivalent to a dynamo/dynamo hub. Note to keep in mind reading the following sections: This means it would be possible to extract more power by making sure the curve of the power through the LED is at 2.4W at 6V. So it would be possible to extract more power at higher speeds with a current doubler or tripler. In practice it looks like lamps such as the Edelux, Cyo, and others are fixed to give almost maximum output at 6Veff, which is equivalent to riding 15 km/h because the dynamos and dynamo hubs must produce 6V 3W at that speed. Perhaps this is done because it's difficult to make such a power curve work, for various current sources (dynamo, dynamo hub: they don't all act the same to non-resistive loads...). And an option of e.g. letting a current doubler/tripler kick in at 20 km/h is problematical because you don't know how fast a bike is going. Pulses won't work as these depend on the number of poles of the dynamo hub, and the pulses come much faster with a standard dynamo. Also, determining speed by the power that the dynamo can deliver is a problematical way to do it as what you can extract from the dynamo hub can vary depending on your circuit (this is not a simple resistive load, unlike a direct circuit with incandescent bulbs)... So what this means is that you would need to figure out from the power your circuit uses, what Veff would be, and then adjust the power if necessary. All in all these considerations are probably the reason (or another reason) why StVZO headlamps seem to be limited to 2.4W as limiting power to 2.4W is much easier. Actually, the power could be higher at lower voltage too! The only other point specified in TA4 is of 3Veff of which it is said that the lamp must light up...
Thinking about the 2.4W power limit for headlamps and the 0.6W taillamp limit (the latter within +10% to -50%, so a 0.3W taillamp is still ok), I came to the conclusion that these limits aren't there to limit power (and thus how bright bicycle lamps can be) but to guarantee interoperability... [ well, perhaps both interoperability and maximum brightness, see below ] I.e. with any given StVZO compliant dynamo, any StVZO compliant headlamp combined with any StVZO taillamp will work. This makes sense (and this is again something that should have been put into the rules, to prevent people thinking 'why?') and in retrospect obvious but only from a non technical perspective, i.e. if you don't know how a dynamo works this rule is more logical than if you do know how a dynamo works! I don't like these power limits as they restrict what you can do, esp. as it's possible to extract much more power from a dynamo. Esp. with current doubling circuits it's possible to extract a lot more power than 3W even using only 1 or 2 power LEDs in the headlamp. I think a better rule would be to take into account that a dynamo is a current source, so, put a 3W minimum on the dynamo using the resistor measurement (no tuning capacitor tricks to get more power from a dynamo), then put no limit on the headlamp as long as it can power a standard taillamp (perhaps less than 0.6W, wouldn't 0.3 W be plenty with current LED technology?). This assumes powering the taillamp from the headlamp which is the way it's being done with modern lighting anyway.
To get round the StVZO limits I came up with a few ideas to make a lamp run at more than 2.4W, but still be StVZO compliant. One is the 12V method as I mentioned earlier on this page, another is a trick I suggested to someone in lamp design a while back: Put a 2.4W regulated driver in the headlamp, but also include a separate 'special purpose' connector on it. This would go direct to the LED... So, when you use the normal leads you use the 2.4W regulator, but with an external box with alternate regulator you could extract all the power from the dynamo you want! I'm not sure if the StVZO people would allow this, but then again why not? I don't see in the rules that there may not be an extra connector...
Note about the 2.4 W limit with regard to maximum brightness: There is no upper limit to the brightness of the beam, except in the region 3.4° above the brightest spot (I will add a picture with explanation of brightness requirements soon) where the maximum brightness is 2.0 lux. This means, suppose a lamp is approved at 2.4W and has a brightness of 1.9 lux in that region (i.e. the region of light going upwards). As described above it is possible, but perhaps hard, to make a StVZO approved lamp that runs at higher power at higher speeds, because in particular sidewall dynamos and dynamo hubs don't act the same to non resistive loads and you don't know which type of power source StVZO uses exactly. But suppose you had figured out a way to do this and make the power curve go through the 1.92W - 2.64W window in the StVZO test setup. Then at higher power the amount of light going upwards, above 3.4° above the brightest spot, would become larger giving a intensity of more than 2.0 lux if light output was increased enough. Strict reading of the requirements only mentions the measurement of the lamp at 6Veff, so going over 2.0 lux wouldn't go against the letter of the regulations, but it would go against the spirit. So perhaps the 2.4 W limit was intended both as a guard against too much glare for oncoming traffic, and to guarantee interoperability.
When I got the E3 pro (StVZO compliant) on loan to review, it says on the bottom 6V~ and 2.4W. That got me thinking: It wasn't approved as a 12V lamp then, but what about that claim of 305 lumen? Did Supernova achieve a powercurve that goes through the 1.92-2.64W window at 6Veff on StVZO's testbed? Well, perhaps they did or alternatively as I suggested elsewhere, they may just be fooling people with their claims (Update 2011-3-18: This is indeed what's happening, Supernova did nothing clever, they just ridiculously exaggerated the light output of their dynamo lamps). It may also be that that window is broad enough to get through StVZO more easily than I expect. Or something else? To get through StVZO I came up with another method which is actually gaming the system: Take a bunch of lamps, each with slightly different electronics to give the 2.4W at slightly different points. Send all of them to StVZO for testing. One of them will get through as ok on the StVZO testbed, and you then take that particular lamp's electronics and use that for your StVZO lamp series...
Gaming the system is not illegal and in this case not even immoral. I see it as entirely just to work around the unnecessary restrictions in StVZO...
There are apparently possiblities of getting something approved even if it's not legal according to a strict reading of the rules. One example is the SONdelux (which is not the same as the SON20R, but also provides less power than regular 3W dynamos) which was granted approval for use in wheels with 622 mm diameter rim in December 2009, but only in combination with an Edelux headlamp... Note that there are rules about a minimal frequency of the power output from the dynamo hub but especially a minimal power output at given speeds. The SONdelux doesn't fullfil all demands when it's put in a wheel with 622 mm rim (or even 559 mm rim as for mountainbikes). So I think this combination-approval was given because the Edelux gives enough light at low speed with the SONdelux. See also Schmidt's commentary on their news section:
Endlich ist es amtlich: Schmidts kleiner Nabendynamo SONdelux (früher SON 20 R) passt hervorragend zum LED-Scheinwerfer Edelux. Darum hat das Kraftfahrt-Bundesamt im Dezember dieser Kombination den amtlichen Segen gegeben, für alle Laufradgrößen von 16" bis 28". Wir bedanken uns für die Legalisierung des technischen Fortschritts!
So they are 'grateful for legalising this technical progress'. This indeed seems to indicate special approval was granted...
[ Update: Note that the way Schmidt writes it up above, implies that the SONdelux was the SON20R, so just a rename. This is not the case and I think it was intentional so they could remove the SON20R from the lineup and pretend to have the SON20R StVZO approved to make everyone happy: For those who want the least drag as possible the StVZO approval is advertisement, a sign of how good Schmidt hubs are as no other hubs are approved that have less power. For those who want/need a StVZO compliant system and the least drag this is the only option, at least when using an Edelux. I've clarfied this elsewhere on my site. ]
On Schmidt's website, an old page for the SON20R says:
Nach StVZO ist er für 16" bis 20" Laufraddurchmesser zugelassen.
So, only StVZO compliant when put in wheels of 40 to 50 cm diameter.
From Schmidt's newer SONdelux webpage:
Seit Dezember 2009 hat der SONdelux - in Verbindung mit Edelux - die StVZO-Zulassung für alle Radgrößen (16"-28").
So since December 2009 the SONdelux + Edelux combination is StVZO approved for all wheel sizes.
Another case which may be a special approval is the early version of the IQ Fly which used a current doubler and used ca. 3.2 W (See http://www.enhydralutris.com). At least I presume it was approved... Later versions of the IQ Fly have a current regulator limiting it to only using 2.4 W. The same is true for the Edelux which I first assumed also used the standard current doubler and thus more than 3 W, but no, it is regulated to 2.4 W according to measurements on http://www.enhydralutris.com (I'm assuming the measurements there are done on a dynamo; I think I'll have to start doing headlamp measurements myself to be sure of all conditions a lamp is measured under). Does this mean the Supernova E3-asymmetric with 305 lumen was also granted special approval?
Update: The answer is no, as you can read in updates of various sections of this page: Supernova did nothing clever, they didn't get special approval, they just lie about the output of their dynamo lamps.
StVZO doesn't demand a headlamp or taillamp having standlight. If a headlamp does have standlight, it must provide this function for at least 4 minutes... At first this may seem odd. Why demand 4 minutes when anything over 0 seconds is more than a lamp without standlight provides? This is again a case of 'why don't they just include an explanation?'. Thinking about it for a bit, I think this is the reason: If you have a headlamp with standlight, you are counting on being visible for a while, and your behaviour may change as you are depending on that. So, if you have a lamp with standlight you will rely on having that and then it's reasonable that the duration that standlight works is more than in typical situations where it's 'used', e.g. standing still waiting for a trafficlight.
For taillamps there's an interesting demand if they are dynamo powered: They must shine some portion of their light upwards/forwards (towards the rider). I don't see that this will be of use when someone in a car is supposed to notice you, but I do myself often glance back at the taillamp when I start cycling to make sure it works (sometimes it doesn't, because a cable got loose for example). Could this be the reason for this rule? With battery powered rear lamps, you go to the lamp, switch it on, you know that it's on then (or if not you will start looking for the problem), and then you go off. So there you don't need to glance back while riding to see if it works. This makes sense. An aberration to this (i.e. not fitting this reasoning) is that there are taillamps that are battery powered but automatically switch on when movement is detected. But of of course they won't switch on if the battery's dead or there's a malfunction but you won't necessairly check for this. Perhaps that's something not taken into account by the StVZO rules? And what about the case where you ride on 2 bicycles, one with dynamo lighting, the other with dynamo lighting + battery powered rear lamp. In this case there's a lot of chance you forget to switch on the rear lamp because that's not required with the full dynamo setup, but when you glance back you may remember 'ah, I'm riding the bike with battery powered tail lamp'. You may or may not remember that you switched it on (such things become automatisms and are hard to remember if you performed them that specific time) so the cone forward would be as useful in this case as it is for full dynamo powered lighting. All in all I think this distinction in dynamo/battery powered rear lamps is a mistake.
As I said earlier on this page: LED lamps are apparently not a "bauartgenehmigte" light source (bauartgenehmigt = approved for the given use), and for such lamps the rule is that the light source must be fixed in the headlamp.
What was not clear was what this meant exactly, as you can still see from my speculation about this on various parts of my pages on bicycle lighting, i.e. how is this supposed to be interpreted? (This is again a case of "why don't they just explain that in the law itself?"). From analysing various lamps and using the information I got from someone who tried to open the E3-pro-StVZO, I can finally draw some conclusions as to how one must interpret this requirement. I will begin by listing 3 lamps:
Thinking about these different cases I came to the following conclusion as to how the 'fixed' requirement is interpreted by the StVZO people (or the StVZO testers, not sure):
This reasoning can explain why the Edelux, E3-pro-StVZO, Philips SLD are difficult to open, and why the Philips LBL, despite being easy to open, is still StVZO approved.
Update (2011-3-18): I got an email about the B&M Cyo which is apparently fairly easy to open (screw on the bottom) and then the LED on a star can be easily replaced. If this is true my reasoning may not be complete, or even wrong (oh, the horror! ;-)). Alternatively, it could be B&M changed the Cyo from the model that was approved. If that was different than the current version, they could get into trouble with the StVZO people... All speculation at this point, I will investigate this issue.
On my page about annoyances from lamps, there's a section about the problems cyclists have riding on roads parallel to a road for cars. When analysing the circumstances but especially after 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. 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! 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) Also note that bicycle lamps are since several years in StVZO required to be at least 10 lux. 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.
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? Do the StVZO people actually ride bicycles?
So it's no wonder that the Edelux which puts out ca. 80 lux at the top of the beam (where that hits the road depends on how far you aim the lamp of course) is just about the absolute minimum to see on an unlit parallel road without getting blinded by car headlamps.
Another piece of the puzzle is, I think, not just due to the light of car headlamps not being cutoff enough to the sides, but that if you're riding on the same road as an oncoming car, its headlamps will light up the road you are riding on enough for you not to be blinded, whereas that is not the case on parallel roads. This is comparable to the situation where I got blinded by the Magicshine, but not by the Lupine Betty because the latter lights up the road much better.
And then we have the asymmetry present in some car headlamps left-right. The right hand side can have a section pointing up. I first read about this a year or so ago (I think on rad-forum.de or perhaps mtb-news.de) that this is meant to read traffic signs, and in StVZO there's a provision for this but only for Xenon headlamps it seems. But I've seen a picture of this with non-Xenon headlamps. This would explain even more about the problems cyclists have on a road parallel to a road for cars, perhaps this is even the worst problem nowadays.
Example picture from mtb-news.de:
More discussion about this problem to be added...
§67 (3): The middle of the beam (they say 'Lichtkegel' = lightcone) should at 5 m distance be at half the height of where it left the lamp. In an earlier version of StVZO (See for example Olaf Schultz' website) it was simply said that the middle of the beam should be on ground level at 10 m. Why did they reword it this way?
First of all let's look at this:
You may think this is obvious, but it's not. With a symmetric beam it's obvious (well, more or less, you can choose an intersection plane perpendicular to the beam or you can choose a vertical plane as obvious ways to determine the middle), with an asymmetric beam you can talk about the middle in various ways. For example, using the fact that the middle of the beam should be on the ground at 10 m, then you could argue, that with some of the light hitting the ground already directly below the lamp, the light may not extend more than 20 m from the bike! Which would suck for anyone who rides fairly quickly (I have the light of my bike lamps aimed so the cutoff is around 45 m, and for the Philips LBL I have it aimed at 70m).
But lamps always have stray light above the horizon, so that means if you take this into account as well it means you need to aim the lamp almost straight down into the ground!
So, let's assume they mean the light that gets above the cutoff requirement of 2.0 lux. How do you define the middle, i.e. what plane do you intersect with the light beam? A plane which gives you the closest and furthest (horizontal), or lowest and highest points (vertical)? You can also intersect the beam with any other plane in between those. Which should one take?
Also, do they mean the middle of the 'virtual' beam or the middle of the beam of light that is observed? Because the beam will hit the ground fairly quickly. Perhaps that's why they changed to 5 m, to avoid this, but putting it this way doesn't avoid this problem because many lamps shine significant amounts of light near the front wheel of the bike.
So, this is not well defined.
My conclusion is that some of the StVZO people (who wrote this about middle of the beam in particular) don't actually understand much about technical issues... (or at the very least they don't think things through). This text about aiming the headlamp in particular is just mind blowingly stupid. The only proper way to aim a headlamp is by looking at the cutoff and making sure that that ends on the road somewhere (I'd say 50-60m maximum), and not horizontal and also not going up into the air.
Now to the 3.4° rule in TA. What does this entail? Well, suppose I have a lamp with the maximum light intensity aimed at 50 m, then the angle downwards of that high intensity part of the beam, is 0.86° (for a lamp mounted at 0.75m) so the region from max +0.86 ° to max+ 3.4° in StVZO's test setup shines into people's eyes. TA doesn't limit the intensity in that region other than implicitly, i.e. it must be lower than the maximum intensity of the lamp because by definition of the TA test procedure, the maximum intensity will be aimed at the 0° line. So the following is possible: Suppose a lamp has a max lux rating of 80, and in the region of +0° to +3.4° it has a light intensity of 79 lux, and above 3.4° it is less than 2.0 lux. The cutoff transition region (+0 to +3.4°) should be part of how you aim, but as StVZO doesn't really regulate this in a proper manner, it's clear that pointing the maximum intensity at the longest distance you want light at, may not be possible without blinding traffic (with that 79 lux at 10m). In that respect, the cutoff as defined in StVZO for lamps that can light up the road at long distance, is not strict enough (assuming you want the maximum lux rating pointed far away, as that will give the throw), and the transition region in this example has a significant part in how well the lamp lights up the road at long distance. You could argue that there is no proper way to point the lamp with the StVZO requirements.
It's clear that opposing traffic should get less than 2.0 lux (at 10m) into their eyes. At least, that seems the intention of StVZO and seeing how annoying car headlamps often are, 6.25 lux at 10m is too much (laws should take into account mounting height and emitting light area, so that both are equally blinding, though perhaps technically it's not really possibly to do better?). Therefore, the aim should be such that the 2.0 lux region at worst starts at the horizon (from approximately the centre of the headlamp's lens). This means, using the 3.4 degrees below which the intensity increases up to the maximum, that the maximum is pointed at -3.4° which means for a headlamp at a height of 0.75 m (centre of the lens), the spot of maximum brightness will hit the ground at 12.62 m from the front of the headlamp! That's not a lot! This means in practice, all bicycle headlamps are aimed too far, and thus opposing traffic gets more than 2.0 lux into their eyes. This makes it really clear why the region from 0° to 3.4° in which the light intensity decreases from maximum to less than 2.0 lux, is of significant importance in how one should aim a lamp for best throw. It is also obvious that 3.4 degrees is actually a lot (a tenth of a degree makes a large difference) in throw, and the precise decrease in light intensity in that section is of significant influence on a lamp's throw. This means, even though bike lamp designers are having trouble meeting the StVZO requirements while achieving a high maximum lux rating, that actually, the requirements are not strict enough. This will become important when people start riding around with 600 lumen headlamps with cutoff! Note also that even though it seems the requirements for car headlamps are far lower than for bicycle headlamps, that after having done this analysis it's clear that this is not actually the case because with car headlamps, the aim is included in the testprocedure, so opposing traffic will get a maximum of 6.25 lux into their eyes, while with bicycle headlamps, in reality, there is no maximum!
After this analysis, I got the idea that the light coming above the horizon from the Philips LBL could be more than 2.0 lux, and that that is caused by the transition region from the brightest point, to the region where brightness must be below 2.0 lux. This I thought could be the reason that I felt the lamp was barely tolerable in annoyance when riding towards it (and why some of those in the group of cyclists I encountered thought the same thing; see the review of the Philips LBL). However, that might not have been it, perhaps even the 2.0 lux which most old incandescent headlamps won't get to I suppose, is already annoying. See the following for more on this problem.
Update 2011-12-13: On the page with the review of the Philips LBL I added a section on getting blinded. It could be actually due to artefacts above the horizon (see the wallshot of the LBL). I will investigate this further.
This section will be expanded with more calculations/examples/pictures.
Example: Take a bicycle lamp mounted at 1.05m, that's pointed with the cutoff at 70m (such as a Philips LBL).
1. The eye height of the driver of a car is at ca. 1.10m, so he gets the light at about 1.14° above the maximum intensity in his eyes at 10 m from the lamp. This is likely more than 6 lux.
2. An upright riding cyclist with eye height of ca. 1.80m gets les than 2 lux in his eyes (4.3° + 0.86° > 3.4° of StVZO, so in the 2 lux region).
3. Someone riding at eye height of 1.5 m (road bike) gets to about the 3.4° so it's marginal there.
At somewhat larger distance, say 15 or 20 m the cyclist will get more into his eyes from a region with higher lux rating, but at bigger distance which decreases the intensity, so it depends a bit how the light is distributed from 0° to 3.4° above HV. It seems the StVZO 3.4° region is sufficient in most cases to prevent more than 2.0 lux into eyes of cyclists, but car drivers can get a whole lot more into their eyes!
Note: I will start doing lux measurements of headlamps to check these issues and also what lux ratings the lamps that I have tested get and compare those with the manufacturer's claims.
2012-10-26: After a question on the legality of mountain bike lamps in Germany I added this section:
The only thing StVZO rules is use of bicycle lamps on public roads. It does not rule on what you may call a bicycle lamp nor on what you may do in advertising.
When mountain bike lamps (with circular symmetric beam or more generally any non-StVZO beam) are sold in Germany I suppose on the packaging there should be some notice that using these lamps on public roads is not allowed...
I remember reading on German forums about Lupine who got into some trouble at fairs where they advertised their lamps as bicycle lamps. After such issues they said these were e.g. for walking or other use in outdoor activity. I would have to look it up exactly how this went. But I think the problem they got into was some sort of advertising standards issue and possibly misleading buyers into buying lamps that they are not allowed to use on public roads though they might think so from the term 'bicycle lamps'.
Addition: StVZO §22a (Bauartgenehmigung für Fahrzeugteile), part 22, shows the result of a court case, which disallows offering for sale lights that are not approved, unless they are for vehicles not for use on public roads. So implicitly it's already clear that sale of non-cutoff lamps in Germany as a regular bicycle lamp is not allowed (because it would mislead buyers), but here it's made explicit, not as a rule, but as a court case.
See Legal use of lights on public roads
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Last modified: Sat Jan 25 16:03:29 CET 2014