Get Some F**king Lights

Ah, didn't make myself clear. I meant what effect would it have on the helmet in the event of an impact...

I'm pretty sure every helmet manufacture has a disclaimer saying that under no circumstances should you attach lights to your helmet. Make of that what you will.

I'm still in two minds about them (both as a driver and cyclist). But I think overall I'm in favour of them.

I have decent non-flashing ones attached to the bike and then smaller, but still bright, flashing ones on my bag - so chest and back.