Re: Do you use dinghy lights?
Good old fashioned common sense surely comes into it, albeit not in a legal sense.
Personally I think its simply silly to motor at speed, no matter what size of craft, without lights. Equally so to row across a channel unlit. Nevertheless rowing or motoring slowly from shore through a field of anchored or moored boats doesn't seem to pose a major risk presuming you have a light handy in case of the unexpected.
“Life is a trick, and you get one chance to learn it.”
― Terry Pratchett, Nation