Five things to know about EMF requirements for lighting products
The objective of IEC 62493 Ed. 1 is to establish a standardized evaluation method for the electromagnetic fields emitted by lighting devices, in order to comply with the basic restrictions given in the ICNIRP (International Commission on Non-Ionizing Radiation Protection) publication “Guidelines for Limiting Exposure to Time-varying Electric, Magnetic and Electromagnetic Fields.”
What lighting products are covered?
The standard’s scope encompasses all general lighting equipment and auxiliaries. Some equipment is specifically exempted. Exclusions include the use in vehicles, built-in components for luminaires and all lighting products without electronic control gear. It is possible to read the scope of the standard free of charge at the IEC Webstore.
What is to be measured and how?
IEC 62493 Ed.1 takes a shortcut to measurement requirements by observing that lighting products already are subject to the radio interference suppression requirements of CISPR Publication 15 (Limits and methods of measurements of radio disturbance characteristics for electrical lighting and similar equipment).
Having noted this, the standard analyses in depth the frequency ranges covered by CISPR 15 and its corresponding emission limits. The CISPR 15 requirements for conducted power line emissions, magnetic field emissions below 30 MHz and radiated electromagnetic field emissions above 30 MHz are analyzed for their effect in the electromagnetic field (EMF) assessment. In addition, the specific characteristics of lighting equipment are considered, for example, the fact that the frequencies used in power converters are higher than 20 kHz in order to avoid audible noise. The conclusion of this analysis is that if the lighting device complies with CISPR 15, the only physical characteristic that needs to be measured to prove compliance with the basic restrictions of the ICNIRP publication mentioned above is the induced current density due to the electric field. The measurement is performed in the frequency range 20 kHz to 10 MHz.
Details on measurement techniques and related test equipment
Electromagnetic labs are already known for their use of test fingers and artificial hands, but now a test head will also enter into service. The EMF standard for lighting devices calls for a test head, or more accurately, a van der Hoofden Test Head. The device resembles a human head in size, but is simply a round metal sphere that is connected to an EMC test receiver through a protection network that has a tightly specified frequency-dependent insertion loss (see Figure 1).
FIGURE 1: Test Setup
The test head is placed at a specified distance from the device to be measured and a scan is performed with the EMC receiver using a specified bandwidth (see Table 1). The resulting array of data is then processed with software that first converts the measured voltages into current density Jcap(fn), taking account of the transfer function of the protection network and the dimensions of the test head, and then compares the current density at each frequency to a limit value Jlim(fn). Finally, a summation is made to obtain the final result F as:
The final result is therefore conveniently expressed as a single figure, which is easy to compare with the specified limit of F=0.85.
The ICNIRP basic restrictions that relate to current density in head and trunk are shown in Figure 2.
FIGURE 2: Limits for current density
Table 1. Receiver settings