The system has an electrical receiving unit (10), and a light source unit (30) with a light source (36) e.g. lamp, and a light control device (35). The control device controls the amount of light guided to the receiving unit based on a comparison of a characteristic value of the receiving unit with a characteristic light source total value. The characteristic value of the receiving unit indicates a relative value of the amount of light guided to the receiving unit, and the characteristic light source total value indicates a relative value of the amount of light conveyed by the source.
