In reply to cliff shasby:
I have two on the front and two on the back - each pair is a main and a reserve/
The main front is a Lezye Macro drive (about £60) - good for up to 26mph on unlit roads - above which it just shows me the hole I'm about to hit.
The subsidiary is a tiny Bontrager flickery thing - about £12 - very good amd sparkly bright and runs off 2xCR2032. Needs a turn of self amalagamating tape around it to really keep the water out.
Back - some Cateye thing - no idea what, but about £30 worth. Bright. The reserve is a Lezyne Femto (i think - the smallest cylindrical thing that they do). Another 2 x CR2032 offering, but pretty crap really, and definitely in the 'reserve category and not as good as the Bontrager one.
The Bontrager one used to give up in the rain eventually, but not now its got the extra tape around it.