Bicycle lamp size (comparison pictures and why a lamp needs to be a certain size)

Headlamp sizes compared in pictures

Here's a picture with a bunch of lamps to show their relative sizes:



Edelux and Betty compared:

Edelux, Philips saferide LED dynamo and Philips LED bike light compared:


Edelux compared to Cyo RT:


Edelux compared to E3-pro-StVZO:


Luxos compared to Edelux:


Luxos compared to H-diver:


Luxos compared to Trelock LS885:


Luxos compared to Dosun U1:


More comparison pictures to come of the Luxos and various headlamps taken with daylight.

Taillamp sizes compared in pictures


What size should a lamp be?

Fashion

In a recent discussion about the subject of lamps that are 'big', I was told a story that's quite understandeable, but it involves a type of reasoning I don't use. A woman has a choice of 2 lamps. One is big with a big reflector/lens, the other small, but it doesn't produce as much light and/or its beam is poor due to the small size (more on that further on). When the big lamp was recommended she said 'but look at how big it is'. No discussion of a tradeoff, no checking if she'd be happy with the light from that smaller lamp, no, how it looks was most important. For me the tradeoff is also there, I choose a lamp I like in beam but also design, but first and foremost stands its performance. This is of course partly due to the fact that I cycle a lot on unlit or poorly lit (country) roads, so I need good light and I know how annoying and dangerous having insufficient light on such roads is.

Reflector/lens size vs. LED die size

The smaller a reflector, the larger the problems become with manufacturing tolerances, esp. in combination with larger die sizes of newer LEDs (that also put out the light with a larger angle which exacerbates the problem). Lenses have been getting smaller and smaller resulting in e.g. the Ktronik Triple XP-G I tested (3 LEDs with a very small lens of just 20 mm diameter), but as the LED die size of the XP-G is much larger than that of the XR-E and XP-E, it's more difficult to focus with a small reflector or lens. In fact, there aren't small optics that tightly focus the XP-G's light. So you must choose what you prefer: Small reflector/lens and a not very tight beam, or a bigger reflector to give a tight beam or better cutoff beam. Esp. for beams with cutoff, making the optics too small is a mistake which means the beam won't get as good as it could be, or manufacturing tolerances will have an effect on how each individual lamp from a series performs, possibly with noticeable deviations compared to the design/reference lamp.

A note on the XP-G (and XM-L) in cutoff optics: Note that the StVZO rules demand the brightest spot be placed at a given line, and 3.4° above that the light intensity in lux may just be 2.0 lux. This is very very difficult to achieve with the XP-G (in relatively small lenses or reflectors) as I've been told by a light designer, and it is evidenced by the fact that there are no StVZO compliant lamps using the XP-G that have a high lux rating. The upcoming Dosun U1 & U2 also don't have a very high lux rating which means it's easier to get to below 2.0 lux, but the downside is that throw is not very far (ditto for their Dosun D1 which uses an MC-E which should produce more than 500 lumen, yet the lux rating they claim is fairly low at about 45). If you think about what a high lux rating means, then you will realise that the higher this number is, the more the throw of the lamp will be. I should say: the more the throw can be, because it depends on the light intensity being still high a bit below that point of maximum intensity. To give some examples: Cyo: ca. 60 lux (at 30 km/h), Edelux: ca. 80 (at 30 km/h), Philips LBL: claimed 80, but measured at 95 (Olaf Schultz). Supernova has put a piece on their website about what they call "the fairy tale of the lux" but they just do that because they can't achieve a high lux rating, not higher than that of the Cyo and certainly not the Edelux. It also means their lamps will not throw as far... I will get into more detail about all this on the StVZO page.

Space for connectors, switches etc.

The Edelux is an example of a headlamp that looks nice but it's too small because for the taillamp you need to use the lamp's mount for an electrical connection. This is bad as that can cause shorts with dynamos that have the earth on axis, but also, it can cause problems with electronics that use the dynamo for input (there is more chance of short circuits when it's wet for example). It's better to use fully insulated wiring. Frame wiring is something bad left over from the time of old citybikes until the 1980s. The other pole goes to a connector in the lamp's mount and that is too tight and the connector is thus surrounded by the other pole which means short circuits can happen easily. So, the Edelux should have been made a bit bigger with proper room for 2 taillamp connectors.

Future

2012-12-21: In November 2010 I made this page after lots of discussions about light design and lamp size, one argument was that the lamp sizes are dictated to some extent by fashion. My view was as I wrote above that headlamps were getting too small, and my advice (to someone wanting to develop a bicycle headlamp) was to go for a bigger lamp, irrespective of fashion. I think the Luxos lamps will mean other manufacturers will follow if they aren't/haven't been planning larger reflectors already. The advantages were always clear, and the reality of LED die sizes not shrinking but increasing in size, together with more light output that can and should be distributed over a large area, have more or less forced the issue that seemed clear to me in 2010 already. Also, nobody ever complained about old halogen headlamps being 'huge'... Of course, if LEDs can be made with smaller die size in future, then we could again see the best headlamps with quite small reflectors...

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