Modulation system and modulation method

A method for modulating an input signal in a system, the system including:

• (i) a first modulator configured to (i) generate a control signal, (ii) modulate an input signal according to the control signal, to control luminance of a first light source and (iii) output the control signal to one of second modulators;
• and
• (ii) the second modulators configured to arrange in a predetermined order to form an array, each of the second modulators configured to (i) acquire the control signal, (ii) modulate the input signal according to the control signal, to control luminance of a second light source, each of the second modulators outputting the control signal, the method comprising:
• generating, by the first modulator, as a light information signal, the control signal for transmitting a visible light signal by change in luminance of the first light source;
• acquiring and outputting, by each of the plurality of second modulators, the light information signal in accordance with the order in the array of the plurality of second modulators, such that the light information signal output from the first modulator is relayed from a top to an end of the array;
• acquiring, by the first modulator, as an input light information signal, the light information signal output from an endmost one of the second modulators in the array;
• and
• determining, by the first modulator, whether or not at least one of the plurality of second modulators has failed based on the input light information signal.