ECE regulation for retro-reflector
III.Requirement of illuminating surfaces
a.Class IA and Class IB
The illuminating surface itself shall be limited to 100 cm2 though the surfaces of the retro-reflecting optical units need not necessarily attain this area.
b.Class IIIA and Class IIIB
The illuminating surfaces of retro-reflecting devices in Classes IIIA and IIIB must have the shape or an equilateral triangle.
The outside edges of the illuminating surfaces of triangular retro-reflecting devices in Classes IIIA and IIIB shall be between 150 and 200 mm long. In the case of devices of hollow-triangle type, the width of the sides, measured at right angles to the latter, shall be equal to at least 20 per cent of the effective length between the extremities of the illuminating surface.
The light emitting surface of the retro-reflecting device must be at least 25 cm2 .
“E /ECE/324/Add.2/Rev.4− E /ECE/TRANS/505/Add.2/Rev.4, Uniform provisions concerning the approval of retro-reflecting devices for power-driven vehicles and their trailers”