Hi ---I found this in UK law.???
Type
Position
Specification
Side retro reflectors
Vehicles first used before 1 April 1986 and trailers manufactured before 1 October 1985 require two side reflectors positioned:
not less than 350 millimetres from the ground;
not more than 1,500 millimetres from the ground;
so that the front side reflector is towards the centre of the vehicle, and the rear one within one metre of the rear of the vehicle.
Vehicles first used on or after 1 April 1986 and trailers manufactured on or after 1 October 1985 require side reflectors to be positioned so that one reflector is within 4 metres of the front of the vehicle, one within l metre of the rear of the vehicle and so that there is no gap of more than 3 metres (4 metres if this is not practicable) between any two adjacent reflectors.
Side reflectors must be:
amber (red if within one metre of rear of vehicle);
in accordance with specified angles of visibility for new vehicles, otherwise plainly visible to the side;
not triangular in shape.
Frank