I think they're the same as the ones I have on my cage:
They lasted a day before I cowled them - the glass was bringing light directly into my eyes through internal reflection and the beam lit up the road, the trees, the bonnet, the cage, the dashboard, the wipers, George's lovely smile...
They're the same diameter as heavy-duty plastic drainpipe, the full-round downpipe type, so I drilled three holes and screwed bolts in around the circumference of the light to clamp it. Wasn't sure if it'd work, but they're still there. So I guess that means I ought to tidy them up a bit.
Naah.