B&M IQ-X dynamo headlight review

You may remember, dear reader, that back in March 2016 I mentioned I’d taken ownership of the new Busch and Muller dynamo headlight – the IQ-X. After ten months of the worst Scotland can throw at it, let’s see how I got on.

(Bit of testing context: my other good lights are a dynamo Busch and Muller IQ2U and a battery-powered Exposure Strada Mk2, and I’ve previously owned a Supernova E3 pro. My dynamo is a SON delux in a 622mm wheel, which produces a bit less power – and drag – at lower speeds than a standard pairing.)

The B&M IQ-X headlight

As we discussed last time, the B&M light lineup is now forked at the top. The Luxos IQ2U (they’re really not great at names) that I reviewed here remains at the top of the range despite a slightly lower output thanks to its cache battery, remote switch, USB charging and general electric fanciness. The IQ-X (this light) feels more like a direct challenge to Schmidt’s Edelux lights – something to go for if you’re only interested in the light output rather than any bells and whistles.

B&M IQ-X - what's in the box

Two bonus points before we get started – as the light meets German road regulations it’s one of the few options that meets the letter of the UK lighting regulations (very few UK lights bother getting the kitemark, which technically means they don’t count as far as the Road Traffic Act is concerned). That little optional reflector will also tick another Act box.

And before I forget – £110.

The light output

Yup, it’s very bright. B&M claim 100 lux, which in useful terms means you can comfortably trundle along at 30kph in pitch darkness (in the dry – nothing soaks up bike light illumination like wet tarmac). However, the useful beam is very narrow. More on that later.

There are three gills on each side (within the dotted rubber bit in the photo below) which leak light horizontally to give some side illumination. It’s better than nothing, but nowhere near as impressive as the wraparound lenses on some other B&M lights. On the plus side, if you’re on a recumbent you’ll get very little foot flash.

IQX side view

When it’s not dark, the main beam dims down and a pair of daytime running LEDs in the brow of the light illuminate for more power-efficient being-seen-ness. The ambient light sensor controlling this works as you’d hope; instantly powering up the main beam when it gets gloomy (say, you pass under some heavy tree cover), but not switching back to daytime running until a good few seconds of higher illumination have passed. This is much better than the IQ2, which regularly ends up toggling between modes if you’re stopped next to a car with a bright indicator flashing.

B&M IQ-X rear spades

The light is powered on and off by a switch on the back, surrounded by a blue-glowing flexible ring. That ring is brighter when the light is in daytime mode, and dimmer when under normal beam. Note that the switch is a toggle with no set positions (it doesn’t stay depressed when on, for example), and only works when there’s some power in the light. As there’s no cache battery, this often means you can’t turn the light on without spinning the dynamo wheel to feed it some power. Not a light for cargo bikes…

Finally, the standlight is a very weak. It lasts for long enough, but the output is pants.

Construction and the mount

B&M make a lot of the anodised aluminium housing for the light, but it feels a little cheap in the hand. It scratches easily (the gash below is where I caught it on the bottom of the garage door).

IQ-X showing scratch

There’s no cache battery inside (the standlight is powered by a capacitor), so it’s lightweight.

Rather than a standard B&M metal loop (compare and contrast below), the IQ-X mount is a more complex hard-plastic and metal thing, with freely rotating joints at either end of a short strut. Whilst this allows a lovely range of positions, it’s challenging to get the joints tight enough to prevent the light position moving if it’s knocked. I’d have liked to see some ratcheting to really lock the position.

B&M IQ-X and Luxos - side on

On the plus side, you can remove the strut and merge the two joints into one. On most bikes, I reckon that’s your best bet, as it makes a very solid unit.

Inputs and outputs

The IQ-X has a fixed cable (presumably to improve waterproofing) to connect to the generator (the cable is stripped at the non-light end for you to wire-up your generator connector of choice). This is 60cm long, which is fine for most uprights, but is going to be on the short side for recumbents – you’ll need to add in some connectors and another piece of wire. I’d prefer spades directly on the light, but it’s not a major thing.

Output to the rear light is by a pair of spades on the back of the light.

Three good things

The moving light output really is impressive

There’s no arguing that B&M have managed to squeeze a huge amount of photons from this little light. So long as you’re moving above 5kph, you’ll be impressed. It’s noticeably brighter straight ahead than the IQ2.

It’s a compact, single-purpose unit

Whilst I liked the extra features on the IQ2, they definitely reduced the reliability – it took three versions of the light before B&M sorted the water ingress faults.

The IQ-X just does light, and wraps that up in a small package that would suit any bike. If illumination is all you want, then that’s a good thing. The light weight also helps with stability on the mount – it bobs up and down a little less that the IQ2.

I’ve had no waterproofing or reliability problems

and am therefore pleased to award the coveted Waterproof In Scotland badge to the IQ-X.

Three bad things

The beam is too narrow

In focussing all the output from the LED directly ahead to hit that magical 100 lux figure, B&M have made something akin to a laser… If it’s outside a narrow degree arc from the front, it’s going to be near invisible.

Two examples. Take a standard lane-in-each-direction road, in complete darkness. If you’re cycling in the centre of the left-hand lane with the IQ-X, you may not see a road joining on your right as almost no light will reach the opposite verge. Or, take a winding single-lane road. As you lean the bike to take a right-hand bend, the right side of the beam dips too, and you cycle into complete darkness.

I’ve often praised the way German light manufacturers make the best use of every photon by focussing the output into useful areas. With the IQ-X, B&M have gone too far.

The switch doesn’t work if you’re not moving

Bit of idiocy this – because the switch appears to be electrical rather than mechanical, if the light has no power then you can’t use the switch. Most of the time this isn’t a problem – just leave the light on the entire time. When you stop, the capacitor will run down and shut eventually off the light. Come back to the bike, and the light kicks in as soon as power starts feeding in from the dynamo.

However, if the light is switched off (say you’re in a station where they take a dim view of bright white lights on platforms, or someone helpfully turns your light off in the parking racks at work) and then the capacitor runs down, you can’t turn it back on again without spinning the wheel to feed the light some juice.

This is an inconvenience on an upright, but on a recumbent it’s a pain, and on a cargobike might be impossible without help (particularly on front-loaders, where you can’t reach the light when moving).

The standlight isn’t good enough

A bit more picky when compared to the issues above, but the lack of oomph to the standlight would make me nervous if I was sat in a junction waiting to turn across traffic. All dynamo lights without a cache battery are going to suffer from similar problems, but with the IQ-X it’s particularly bad.

I’d supplement with a battery light if I was doing a lot of urban riding in the dark. Or buy the IQ2, which has that cache battery to keep the light bright when stationary.

Would I buy it again?


Not in any way because it’s a bad light, but because if I was just after a very bright dynamo headlight I’d buy the Edelux 2. That uses B&M optics and is as bright, but also bundles in some legendary Schmidt reliability and comes with a proper switch. It’s £20 more, but I reckon you get your money’s worth.

If I was instead after something that really shows off what a dynamo can do or I wanted a commuting light, I’d stick with the IQ2 I reviewed previously. That’s £25 more, but you get better side visibility (both to see with and be seen by), a much more powerful standlight, and the occassionally useful remote switch with USB charger.


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“However, if the light is switched off (say you’re in a station where they take a dim view of bright white lights on platforms, or someone helpfully turns your light off in the parking racks at work) and then the capacitor runs down, you can’t turn it back on again without spinning the wheel to feed the light some juice.”

Your light is probably faulty. The capacitor should not discharge while the light is switched off, so I’m informed by people who know about these things. This does seem to be a common fault on these lights – mine has it, and several other people have mentioned the same thing – but if you contact the retailer, you should be able to get it mended or replaced.

Thanks for the tip. I’ve noticed a long thread on the yacf forum about similar issues, so I’ll update the review to summarise! Possibly my claims about improved reliability were somewhat optimistic…

Having had my IQ2 since 2013 (using silicone to stop it leaking) the cache battery has now given up the ghost and this makes the light noticeably worse. The standlight is now very feeble, and I have to ride for several minutes before it works at all. The “high power mode” no longer works and neither does the USB charger. While I agree that the cache battery made the IQ2 a really good light, it doesn’t last forever.

Hy, i did use IQ-X in combination with B&M Toplight Flat Plus LED with parking light and a Shimano DH-3N72 hub dynamo…
It was good for only one month. IQ-X got faulty. I did replace it by the previous B&M Lumotec LYT B Plus LED, 20 Lux with parking light (which was delivered with my VSF T300 bike). I also noticed that i couldn’t turn off light with dedicated button.. and the capacitor always had to discharge completely.. Got used to that annoying and unexpected fault.
The german seller did replace it within a month… 6 month later… still not installed…
And i agree with you about the too narrow beam: I’m used to start cycling between 5/6 AM for a 60 to 100 km journey. And i’m happy to use a GPS with road/turn indication. It’s a pitty, you can’t read road indications/panels even if they’r installed at one meter from the road border.
I’ve also been thinking bout using a secondary lamp (DC) for panels reading…
The IQ-X light output is perfect… housing and waterproof are good enough…
But i seriously think about a DC front light with more than 6 hours capacity. They are so much powerfull.

Would be possibile to power this front light by a USB power bank ? Could it work ?

My idea is to solder a female USB to the light wire and power it via a power bank stored in my handlebar bag. Nice, clean and not to heavy,

Strange none is producing such a front light … ?


I’ve owned both and have to say that the Luxos U’s beam pattern isn’t exactly wide either at close range – the beam pattern up close has two clearly distinct shapes: one is stronger which projects all the way for you to see further out; the other two are on either side which are both weaker. Once your eyes adjust to the light used to see further out, you already know what happens when you look to the sides with a light output that is inconsistent. The IQ-X isn’t without problems as well: there is a distinct black spot right in between the light project out to infinity and the light put out in from of you. Ignoring the lights to the sides, the Luxos U has a much smoother beam pattern compared to the IQ-X

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