I've been using a Lezyne mounted in an Exposure joystick bracket.
I got ours from on one , £1.99.
Both too large. 🙂
Needs to fit in a vent on the rear as there's a front light on top.
Have look on our Flickr Stu , they fit in the vents on fox flux .
I have an Ember light on my lid, one of [url= http://www.evanscycles.com/products/bontrager/glo-ember-light-set-ec036129 ]these[/url], neat, plenty bright enough.
Mr beanZ.
They look like what I'm after but can' find them on the on one site?
Bugger , no I can't find either . Cycle solutions have them but a bit more than a tenner .
https://www.cyclesolutions.co.uk/p23264/smart-micro-rear-led-light
Be aware, many helmet mounted rear lights are not visible when you are leant down on the bars, especailly combined front/rear where you might have it mounted further forward so it points forward correctly.
I saw 3 people (other than me) with rear helmet lights this morning on my commute, none of the rear lights were visible while they were riding, only when stopped at the lights and sat up away from the bars. Im sure they thought they were visible all the time.
[EDIT] also worth noting i was on a bike (and 6ft4) so was also much higher than the eyeline of drivers and still couldnt see the lights.
I've got one of these on the rear vent of my helmet. Works well for me.
http://www.decathlon.co.uk/vioo-100-rear-led-bike-light-black-id_8322808.html
i put the aldi moon copy on the back of my helmet and tilted it kinda down.
I also have a very sit up right bike so the lights visible
Exposure Micro RedEye if you're using a joystick?
