Firstly its a European standard for helmet design/manufacture; EN 1078. The claimant routinely offers a discount of 20% following Froom but as you will know Whitwood wanted that increased. I do know the CTC got 15% thrown out in the case of Millet.
Is there an assumption that helmets should be worn? In 1999 the TDF pelaton rode bareheaded, but to see a rider descending without a helmet during this years' tour would be unthinkable. Although I wouldn't wish it upon anyone, a judge in a contemporary case will provide the last word on whether damages should be reduced or not. I suspect that as time goes by, and it becomes less accepted to ride without a lid, the defence of contributory negligence will become the norm (where the lack of helmet is proved to have increased injury).
they are not just good in the dark they work well in poor visibility and can help you see a vehicle in which the numpty driver hasn't bothered to put any lights on to make them stand out from the mist drizzle etc. grey BT vans were an awful colour for merging into mist . silver cars are as bad. 
