Light-emitting diode (LED) lamps have been widely introduced in clinical settings for energy conservation and cost reduction However, LED lamps radiate electromagnetic noise and they cause poor reception of broadcasting and wireless communications. In this study, we investigated the effects of LED lamp use on the electromagnetic environment surrounding wireless medical telemetry systems and discuss the safe installation of LED lamps in a clinical settings. Streszczenie. Oświetlenie LED jest szeroko stosowane w klinikach medycznych, pozwalając na oszczędność energii i redukcję kosztów. Źródła światła bazujące na diodach LED emitują szum elektromagnetyczny powodując pogorszenie komunikacji bezprzewodowej. Artykuł przedstawia badania wpływu lamp LED na elektromagnetyczne środowisko obejmujące bezprzewodowe systemy telemetrii medycznej i omawia zasady instalacji lamp LED w obiektach medycznych. (Kompatybilność elektromagnetyczna medycznych systemów telemetrycznych i oświetlenia LED).
To evaluate the electromagnetic interference (EMI) in a wireless medical telemetry system (WMTS) caused by LED lamp emission, the statistical characteristics of noise and its impact on the receiver sensitivity of the WMTS were investigated. Noise from LED lamp is generally wideband owing to high-speed switching, but the WMTS employs narrow-band reception of 8.5 kHz. The amplitude probability distribution of band-limited noise from LED lamp agrees well with that of Gaussian noise with average power equal to that of band-limited LED noise. The increase in the required signal power of the WMTS for critical reception, caused by LED noise, was almost the same as that in the case of purely Gaussian noise with equal power. The above results indicate that LED noise interfering with a WMTS channel can be well modeled by Gaussian noise, and that the interference effect can be simply represented by the reduction in the receiving carrier-tonoise ratio (CNR), enabling easier evaluation of the impact of interference in the WMTS by using the CNR.
Switched mode power supplies built in LED lamp radiate electromagnetic noise (LED noise) and may interfere with wireless medical telemeters (WMTs). We conducted research on statistical characteristics of LED noise and its effect on the receiver sensitivity of the WMT. We measured timedomain waveform of LED noise. At the wideband reception, LED noise has impulsive characteristics due to high-speed switching, but this impulsive nature is difficult to identify when the narrow bandwidth. Additionally, this noise is to be approximated as Gaussian noise, because the WMTs use a narrow reception bandwidth of 8.5 kHz and LED noise was limited to this bandwidth. We investigated the required signal power of the WMTs for critical reception under interference by LED noise and for comparison with Gaussian noise. The LED noise and Gaussian noise induce similar degradation in the WMT, confirming that the Gaussian approximation is promising for the evaluation of interference in the WMT caused by LED lamps. Moreover, we showed an experimentally investigation of spatial distribution of LED noise around an LED lamp and its power line under the basic configuration. The spatial variation caused by a standing wave of the disturbance current was observed in the parallel direction to the power line, and the noise amplitude was decreased away from the power line in the perpendicular direction.
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