Abstract: A system for open space data communication comprising a transmitting device and an optical receiver using multiple varying levels of emitted radiation output. The transmitting device includes multiple emitter groups that are capable of being switched on and off and each of which can be activated in parallel to emit fixed, varying radiation outputs. A total radiation output emitted by the transmitting device is defined by a sum of the emitted radiation outputs of the emitter groups, wherein to transmit a bit vector (b0 . . . bn) an emitter group assigned to a most significant bit (b0) emits a maximum radiation output Pmax and emitter groups assigned to the less significant bits (b1 . . . bn) of the bit vector emit radiation outputs: Px=Pmax/2x where x=1 . . . n.