Illuminating surface of a signalling lamp other than a reflex reflector

A red catadioptric on the back that is not triangular.

The illuminating surface of the retro reflector may have parts in common with the apparent surface of any other lamp situated at the front.

Right Angle Prisms are used to re-direct a beam of light at 90 degrees from the incident direction or used as 180° beam retroreflector.

Retro‑reflector" means a device used to indicate the presence of a vehicle by the reflection of light emanating from a light source not connected to the vehicle, the observer being situated near the source.

But he is perhaps better known for inventing the catadioptric (reflective/refractive) Fresnel lens and for pioneering the use of “stepped” lenses to extend the visibility of lighthouses, saving countless lives at sea.

He is perhaps better known for inventing the catadioptric (reflective/refractive) Fresnel lens and for pioneering the use of "stepped" lenses to extend the visibility of lighthouses, saving countless lives at sea.