Measurement and modeling of electromagnetic noise from LED light bulbs

The characteristics of broadband noise radiated by LED light bulbs were investigated. According to the measurement results of the noise waveform in the time domain, LED noise can be categorized as intermittent type or non-intermittent type, in accordance with the operation of the switching power supply installed in the LED bulb. Intermittent-type noise is emitted by some LEDs supporting dimmer operation, and its repetitive bursts are synchronized with the AC mains frequency. For both types, the noise is a sequence of short pulses, each of which is generated at the instant that the power-supply circuit of the LED bulb is switched on or off. Hence, an "on pulse" and an "off pulse" are alternatively emitted. The interval of the pulses varies with time in general. A time-domain noise model representing the time-varying pulse interval and amplitude was developed by applying amplitude and frequency modulations to a regularly repetitive pulse train. As a statistical property of LED noise, amplitude probability distribution (APD) was also measured with various resolution bandwidths of the receiver. When the bandwidth was larger than the switching frequency of the power supply, Middleton's class-A model gave a good approximation of the APD. For narrower reception bandwidths down to 1 kHz, the noise can be regarded as Gaussian for non-intermittent type or intermittent Gaussian for intermittent type, respectively.