This work introduces a novel Physically Unclonable Function (PUF) based on the characteristics of Light-Emitting Diodes (LEDs) and Light-Detecting Resistors (LDRs) as long as these are combined. Specifically, we profit from the variations in the optical output of an LED caused by process variations, as well as from the variations in LDRs. In this way, our work allows for providing a PUF based on optical components, whose electrical response is a function of the used components. Notice that the electrical response refers not only to the static but also to the dynamical behavior. This way, a unique, double-component system can be easily constructed.