A substantially planar light replication or re-transmission component having an incident light receiving surface and an opposed light emitting surface. The component comprises a substantially transparent planar substrate, one or more bipolar junction transistors provided on said substrate, the or each transistor comprising a collector region adjacent to said light receiving surface, an emitter region adjacent to said light emitting surface, and a base region between said collector region and said emitter region, and circuitry for biasing the bipolar transistors in use. The or each transistor is configured and biased in use so that said collector and base regions of the transistor operate as a photodiode whilst said base and emitter regions operate as a light emitting diode.