Abstract: A message transmission system comprises a transmitter and receivers, the transmitter comprising a generator for generating a digital data signal representing a message, and an encoder for encoding the digital data in a serial code having a first and second frequencies representing respectively digital data signal first and second logic states. A modulator is connected to at least one source of visible light for modulating the intensity of light emitted by the light source with the serial code. The light emitted by the light source has two distinct intensities when the light intensity is modulated with the first and second frequencies. Each receiver comprises a detector sensitive to the visible light emitted by the light source for converting visible light emitted by the source into an electrical signal having two states depending on the intensity of the visible light detected. A decoder reconstructs the transmitted message from the electrical signal.