[Legless]

Hi all
I had a search and couldn't find any info on this but didn't want to start a thread on it. I was removing a few bits from the back of my car and was wondering about the reflectors..... are they an ADR requirement and if so what is the authorities justification for requiring them? I've got a few vehicles and none of them have reflectors. I'm guessing most probably fall off at some stage.

cheers
Legless