Busch & Müller IQ Cyo RT (= Cyo Nahfeld with daylight running lights)

Tested: From 17 Nov. - 6 Dec. 2010

I've never been a fan of the Cyo for technical reasons, and only the Cyo-R (Nahfeld = near-field) seemed somewhat useful to me for its near field light when I first made my bicycle lighting web page. I also never liked the fact that B&M made 4 different versions of both the standard and Nahfeld version and since August 2010 5, with the daylight running-light versions, so 10 Cyo versions in total, which just seems ludicrous and confusing if you want to know which one to order. In August 2010 I tested the Philips LED bike light and it was such a huge jump in good usable light despite not a huge jump in claimed light output compared to an Edelux, that I started considering testing the Cyo Nahfeld just to see how dim its beam would be... So, here's a test of the near field version of the Cyo with daylight lights, and you can now see how good or bad these headlamps are:


B&M IQ Cyo RT packaging

Mass: ca.109 g.
Size: width: ca. 51 mm, height: ca. 65 mm (without mounting bracket), length: ca. 66 mm.
LED: Cree XR-E cool white
On/off: There's a rotating knob at the rear with which you can select on, of or automatic (switch on when it gets dark).
Price: €95,-


Mounted on a bicycle it looks like this:

B&M IQ Cyo RT mounted on bike, front view B&M IQ Cyo mounted on bike, side view B&M IQ Cyo mounted on bike, top/rear view

The Cyo RT is the daylight running lights version of the Cyo Nahfeld (Cyo with near-field illumination). These running lights consist of 4 small LEDs beneath the reflector.

I always thought the Cyo's were pretty ugly but the Cyo RT looks ok. I'm not particularly fond of the general Cyo design: The housing is plastic, from which an aluminium cooler for the LED sticks out. There is an advantage of a partly plastic housing though, as it saves weight. The lamp mount is stainless steel, with a stainless steel bolt/nut using torx (a torx key is included). Torx allows more force, and is sometimes used to prevent theft (security by obscurity), but don't count on this: you should note that a torx bolt can be also be unscrewed simply with a regular screwdriver (of the right size)... The lens on this lamp does let light go directly upward, but the aluminium cooler extends over the top of the lens so blocks that from your view.


The beam shape is a weird trapezium shape, I'd seen it before on a forum but thought it was due to having set the angle of the lamp such that it aims far too low and thus projecting this shape onto the ground (similar to what happens with a shot of a light beam on the wall). That wasn't it. The beam shape as shown on Busch & Müller's website is not quite what I see, or due to the way they photographed in the tunnel it doesn't appear as such, as the beam flares out much more at longer distances, with very sharp corners. I don't like this beam!

From talking with someone about this, who made some interesting points about beam shape of lamps at home, and that your attention would go to the shape if e.g. a lamp pointed a triangular beam upwards to the ceiling, it could be that those sharp corners in the beam of the Cyo are a big problem causing my annoyance as my attention often goes to how far to the left on the green bits beside road the left point is, etc. So after thinking about it, it seems likely to me that the problem is with those sharp corners in the beam, which, just as the bright spot in the center of the beam, attract attention.

I had seen some comments on forums about the Cyo (here are some more examples from a year after my review of the Cyo RT of people who feel the same: recent messages on rad-forum.de (in German)), that these lamps give a feeling of being trapped in a tunnel of light, and after experiencing the Cyo RT, I understood this very well. What may not be apparent unless you give it much thought and/or have experienced lots of beam shapes/artefacts, is that the lack of other artefacts outside the trapezium that the Cyo R/RT lights up, is helping this feeling. Artefacts such as the old version of the Edelux has and that the Philips SLD has, are not necessarily bad. They help avoid this feeling of being trapped in a tunnel of light. The only beam shape where this is not an issue is a wide beam shape. Examples are the E3-pro-StVZO, and in battery lamps the QL-269. If the Philips LBL didn't have artefacts it wouldn't matter as it has a wide and very long beam.

The beam is pretty dim compared to other lamps (Edelux, Philips SLD, Trelock LS885). The Trelock LS885 seems brighter and despite patterns in the beam, I prefer that. The beam of the Cyo RT (which is the same as that of a Cyo-Nahfeld, i.e. Cyo with close-field illumination) is not very even as I mentioned earlier, as there's a quite bright spot in the middle (rough estimate: about 8 m from the front wheel) that I hadn't noticed on B&M's website but upon checking, you can see it there, but it's somewhat obscured in that tunnel shot, as that has been taken with partially wet ground. My attention while riding is continually being drawn towards this bright spot and where the sharp corners of the beam are. Very annoying.

Here's the picture on B&M's website:

The lamp has a switch at the back with 3 settings: 0, S, T. 0 = off, S=on/off via sensor, T=daylight mode. There's not much difference between the S & T modes: In S, 2 of the 4 daylight LEDs go on, on T all 4. I checked what opposing traffic would see from these daylight LEDs and they're pretty bad (at night, I've not yet checked during the day). B&M has chosen visibility through being annoying. The LEDs are very bright and nearly point sources of light which give the annoyance of sparkling in your eyes, as I described on this page. B&M should get a kick under their asses for not making this light diffuse.

The light colour of those 4 small LEDs is very bluish, actually they seem slightly purplish even, another thumbs down from me for that reason.

Here are some pictures of the running lights at night, from 20 metre away, and a second one also from 20 metre away but zoomed in which really shows the purple colour:

I even see this purple reflected off of white buildings I cycle past. The purple colour may be a result of the transparant plastic that covers the LEDs. With some types of HID car headlamps I get the same extremely irritating colour when cars pass me, so it could be due to diffraction or even absorption/emission in the plastic.

I showed this lamp on my bike to someone, didn't say anything about it, and she said: "The small lights are nice". I waited a bit, talked a bit but not about these lights so as not to give away what I thought of them, then she said: "They shine very brightly directly into your eyes though, can you set them less bright?". Well, I can switch them off, and so I did. Note that in the off setting, there's no standlight which is what function these small LEDs also perfom, similar to the Lumotec oval senso plus.


For background information on making beamshots see: Camera settings, lamp settings and roads used to make the beamshots.

The S and T modes don't seem to differ in main beam strength (at night), so I just took a picture of the S setting which should give the strongest light beam. Note that I mention the beam shape is trapezoidal, but it doesn't come across well in my beamshots. I think I need a longer exposure time to properly show that as the beam is pretty weak when aimed far as I do. Here's an example on the web of the newer version of the IQ speed (also uses the B&M IQ reflector) which is aimed close and on sloping ground, which means the beam is concentrated on a short distance. It shows exactly the beam shape I see, trapezoidal:

Road 2, camera height 1.65m, camera distance: -0.40m, camera aim: 50m on the road.

Busch & Müller IQ cyo RT
lamp on at 0.75m height
Camera: F3.5/ISO80/4s, h=1.65, d=-0.40, aim=50m
(Original 14 megapixel)

The pattern in the light beam near the front wheel:
lamp on at 0.75m height
(Original 14 megapixel)


I hate it (Note that I never felt that way before with any other lamp I used, LED or halogen).

I hate the daylight running lights.

I don't like the beam: What was good in the B&M reflector as used in the Edelux (with the original IQ reflector), is gone, partly because of the diffuser in the main beam which gives the near field light and the shape of the light beam with its very straight edges and sharp corners, but some of it apparently also because the IQ reflector was changed (since December 2008).

So, I was wrong with my original estimate: The Cyo Nahfeld, at least in the incarnation since ca. December 2008 with the second edition IQ reflector (the one with 5 sections instead of 4), is not perfect for people who don't want to cycle very fast in the dark, because the beam shape sucks.

Since the Philips Saferide LED dynamo became available I see no reason for buying any Cyo versions as the Philips Saferide's beam shape is much better and it's much brighter... Well, if you think an automatic on/off is important, that could be a reason to get the regular Cyo (not the T, not the R and not the RT).

B&M's IQ reflector versions

See this page for a description.

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