Transmitting and receiving

A suitable light transmitter and receiver are necessary to transmit data with light. The light transmitter must have a light source which is able to supply light within the specific wave length of 650 nm. A light bulb does not even come into consideration; it emits light with various wave lengths. This mixture of colours is perceived by humans as white light.

Special light diodes (LED = light emitting diode) are able to supply the desired light. They convert the electrical energy into light energy. The light receiver must meet similar requirements. It must be sensitive to the correct range of wave lengths.

There are special photodiodes which are suitable for this which change their electrical resistance depending on the intensity and wave length of the incidental light. If a voltage is applied, it can be controlled by the photodiode: