A lighting system (100), a light source (110), a device (150), and a method of authorizing the device (150) by the light source (110) are provided. The lighting system (100) comprises a light source (110) to emit light (116), a device (150) to control the light source(110), a first communication channel from the light source (110) to the device (150), and a second communication channel from the device (150) to the light source (110). The first communication channel is formed by modulating information in the emitted light (116) of the light source (110). The light source (110) comprises a challenge generator (118), a light source transmitter (112), a light source receiver (122) and an authorizing means (120). The challenge generator (118) generates a challenge with a cryptographic function receiving an argument comprising a first cryptographic key. The light source transmitter (112) transmits the challenge via the first communication channel. The light source receiver (122) receives a response from the device via the second communication channel. The authorizing means (120) authorizes the device (150) to control the light source (110) by matching the received response with a reference, and if the received response matches the reference, the device (150) is authorized. The device (150) comprises a device receiver (152), a response generator (154) and a device transmitter (156). The device receiver (152) receives the challenge via the first communication channel. The response generator (154) generates the response with the cryptographic function which receives arguments comprising the received challenge and a second cryptographic key. The device transmitter (156) transmits the response to the light source via the second communication channel.