Reflectors to the linear smoke detector
Light rays arriving are reflected parallel. Any extraneous light is also reflected in its own direction and
consequently does not reach the receiver.
The retro reflecting prism in the DLR1191 has the shape of a pyramid that's lateral faces are formed by
isosceles orthogonal triangles. Light beams entering through the base are completely reflected twice on
the lateral faces and reflected back through the base. In principle, the reflector foil has the same effect
(function) as the prism.