In one inventive aspect, a transmitter is provided. In the transmitter, a modulator supplies an electrical current based on a digital transmission electrical signal to a white LED, which emits light including a plurality of wavelengths into the air. A light detector separates a light signal component having a blue wavelength from the emitted light using an optical filter and converts the signal component to a monitoring electrical signal. A waveform control circuit outputs a control signal so that the time delay of the waveform of the monitoring signal with respect to the waveform of the transmission electrical signal is less than or equal to a predetermined value. The modulator corrects the amount of the electrical current supplied to the white LED on the basis of the control signal. In another inventive aspect, a receiver is provided. In the receiver, an optical filter separates a light signal component having a blue wavelength and a light detector detects substantially only the light signal component having a blue wavelength.