System for controlling light in dependence of time of flight signal

1. A lighting system comprising:

a lamp arranged to transform electricity into a light beam having properties including intensity, colour, colour temperature, direction and beam cone angle;

a light control system arranged to adjust said light beam properties;

an ultrasonic transmitter arranged to transmit ultrasonic signals;

an ultrasonic receiver arranged to receive reflected ultrasonic signals; and

a processing system arranged to derive a time-of-flight signal representing the time differences between said transmitted and received ultrasonic signals and to send control signals to said light control system in dependence of said time-of-flight signal,

wherein said processing system is further arranged to perform a sound pressure level calibration step wherein an amplitude of the received reflected ultrasonic signal of the receiver is measured and wherein an amplitude of the transmitted ultrasonic signal of the transmitter is adjusted such that the amplitude of the received reflected signal approximates a predetermined threshold value.

2. The lighting system of claim 1 , wherein said processing system is arranged to perform said sound pressure level calibration step in a short period, preferably within first few seconds, after the lamp is switched on.

3. The lighting system of claim 1 , wherein said processing system is arranged to start deriving said time-of-flight signal and sending said control signals after said sound pressure level calibration step.

4. The lighting system of claim 1 , wherein said processing system is arranged to repeatedly perform said sound pressure level calibration step while it is deriving said time-of-flight signals and is sending said control signals to a light control means.

5. The lighting system of claim 1 , wherein said processing system is arranged to start said sound pressure level calibration step with a first calibration cycle wherein the ultrasonic transmitter is caused to send an ultrasonic pulse with a predetermined amplitude and wherein the amplitude of the received reflected signal is measured, and to repeat said calibration cycle with a transmitted amplitude that is increased in each subsequent cycle with a predetermined value as often as necessary until the amplitude of the received reflected signal is equal to or higher than said predetermined threshold value.

6. The lighting system of claim 5 , wherein said processing system is arranged to cause a warning signal of a flickering of said lamp, if the amplitude of the received reflected signal is lower than said predetermined threshold value after a predetermined maximum number of calibration cycles.

7. The lighting system of claim 1 , wherein said processing system is arranged to analyse the dynamic behaviour of said time-of-flight signals and to send said control signals to said light control system in dependence of said dynamic behaviour.

8. The lighting system of claim 1 , wherein said ultrasonic transmitter comprises a horn for reducing the beam cone angle of the light beam.

9. The lighting system of claim 8 , wherein said beam cone angle of the light beam is smaller than 15°.

10. The lighting system of claim 1 , wherein said ultrasonic transmitter and receiver are arranged to transmit and receive ultrasonic signals in a direction extending within the light beam of the lamp.