Dentistry is undoubtedly one of the most visually demanding professions. For the most natural working environment in the dental office, balanced lighting of the entire room is also crucial, an indispensable part of which is the pendant light above the chair. However, this is kept close to the doctor's head throughout the day.

Every device operating with an electric current emits an electric and magnetic field. As an animal species, we have only been experiencing this artificial influence for a little over a hundred years, a very short time in terms of evolution. We have no specific receptors for this invisible field; we can perceive low frequency currents as nerve irritation, and at high frequencies only the thermal effect is officially recognised.

Examination of the brain using fMRI in subjects suffering from electromagnetic hypersensitivity showed activation of pain centers when presented with both a transmitting mobile phone and a non-functioning dummy. Thus, it has been shown that these people are indeed suffering, but that their pain is not related to the electromagnetic field. I. P. Pavlov might have suggested a different conclusion. There are heated and often controversial debates about the effects of the fields and their hygienic limits, with, of course, the economic aspect and the requirement to maintain the current lifestyle in the background. The compatibility of systems in terms of interference and immunity is dealt with in Electromagnetic Compatibility. "A 'system' can be either a technical device or a biological organism.

Electromagnetic compatibility (EMC) is the ability of a system to function properly in an environment in which other sources of electromagnetic signals are present (immunity) and not emit unwanted signals that interfere with other systems during operation (non-interference). With the development of electrical engineering and the increase in the number and complexity of electronic devices, problems with electromagnetic interference have gone hand in hand. The problems gradually evolved from ad hoc solutions to a systematic approach, and in the 1960s electromagnetic compatibility was set aside as a separate field of electrical engineering in the USA. It mainly deals with methods of measuring + reducing interference and testing + increasing the immunity of systems.

Fig. 1: Electromagnetic interference and its paths

From older times you may remember the streaking of the TV picture when vacuuming or the rattle in the car radio. However, events such as an airplane crash (after passing over a transmitter), an accidental rocket launch (in a thunderstorm), a car crash (while passing a transmitter), and false waves on an EKG (an unresistant device) have shown that if EMC is not maintained (insufficient immunity or excessive interference), lives can be lost. The EMC requirements for electrical equipment were enshrined in our legislation in the second half of the 1990s as part of convergence with the EU. Equipment such as medical devices, luminaires, telephones or computers can only be placed on the market if compliance with the EMC standards that apply to them (among other requirements) is demonstrated.

Unfortunately, the Czech Trade Inspection Authority's inspections of LED lighting in 2011 showed that a large percentage of these products do not comply with EMC standards. Experience has shown that for a number of mainly imported luminaires and light sources, the EC Declaration of Conformity is issued on the basis of test reports actually relating to other products, or according to outdated or invalid standards or incomplete documentation. Importers and distributors risk significant penalties, but for users, such devices may represent a ticket into the realm of unreliable equipment or excessive environmental disturbance and possible increased biohazards. It is to the importer's credit if he goes beyond his obligations to have a product tested for which he already has all the documents from a third-country manufacturer.

Standards for luminaires with regard to electromagnetic compatibility of technical systems (EMC Directive):

EN 55015 - Limits and methods of measurement of radio frequency interference characteristics.

EN 61000-3-2 - Limits for harmonic current emissions.

EN 61547 - Resistance requirements.

The aim of these requirements is to achieve a sufficient EMC margin (see Figure 2). The devices are only allowed to produce interference (to the room, to the supply lines) up to a certain limit. At the same time, they must be sufficiently immunity against interference (from the room, from the leads) - interference up to the immunity level must not affect the operation of the equipment. If these requirements are met, the devices can share the same space and supply circuit without loss of functionality and reliability. Standards for luminaires in terms of electromagnetic compatibility of biological systems (LVD)

EN 62493 Evaluation of lighting equipment with regard to human exposure to electromagnetic fields. This standard limits the induced current density (20 kHz to 10 MHz) and the specific absorbed power (SAR) (100 kHz to 300 MHz). The parameters are measured at a distance from the luminaire using a head model. The aim is to keep the electromagnetic effect of the luminaires on humans within the chosen limits. Induced currents irritate nerve endings and SAR (known from mobile phones) expresses the thermal effects of the electromagnetic field. The general EMC requirements in terms of biological systems are determined by Law 1/2008 on Health Protection against Non-Ionizing Radiation, which limits exposure to electromagnetic fields for workers and the public. For example, the limits in force during the RHP period would not allow the operation of a mobile network. The radiation from luminaires lies well below these limits, with higher values measured only inside the luminaire and in its immediate vicinity. This situation arises in a dental surgery when a pendant luminaire is placed above the set near the doctor's head.

Fig. 3: Comparison of two measurements of interference to the mains for a 6 × 80 W luminaire

classic arrangement - unsatisfactory

HLS arrangement - satisfactory

The idea of the HLS® (Holistic Lighting System), more precisely its EMC+ part, is based on the principle of precaution and voluntary reduction of the electromagnetic footprint of the luminaire in the environment. The luminaires developed in this system are equipped with superior suppression elements such as shielding of internal conductors, filter chokes for different frequencies or mains filters. The geometric and topological arrangement of the elements is also very important. In this way, the EMI design margin can be increased (see Figure 2) and human exposure to electromagnetic fields can be reduced. These findings have been successfully used in the design of thin dimmable luminaires with a larger number of fluorescent lamps, which in a conventional arrangement would easily fall victim to their own interference, especially at the lowest power, when the voltage on the fluorescent lamp is surprisingly the highest (the current is most phase shifted and the active power is therefore small). A luminaire with minimised internal disturbance (and hence greater internal EMC margin) produces less disturbance externally and is also more resistant to external disturbance.

The EMC industry is constantly evolving and responding to trends in other industries. When revision A1 of EN 55015 came into force in 2008, introducing the measurement of interference in the 30 to 300 MHz band, many luminaires with electronic ballasts were suddenly non-compliant because the interference was displaced into this "uncontrolled" area. Some countries now measure interference from luminaires up to 1000 MHz. It pays to change for the better. Most EMC measurements and the development of EMC-friendly luminaires are carried out in a laboratory equipped with an anechoic chamber, a large shielded room with walls covered with needles made of absorbent material that does not reflect incident electromagnetic radiation. In this room, the luminaire under test is separated from the surrounding electromagnetic noise. Other key elements are a positionable antenna and a spectrum analyser that evaluates the signal picked up by the antenna. By repeating and comparing measurements, the best arrangement can be found and the most suitable components selected.

Electromagnetic fields surround us at every turn. Mobile phones and GSM base stations, Wi-Fi, BlueTooth and other transmitters fill the space around us with invisible energy of different vibrations. Exposure tests are often carried out at high intensities and it is assumed that the conclusions linearly hold for weak exposures. But this is not so certain. We can take a nice bath in a tub of water. However, the captured spies, very tightly bound, whose captors had a similar volume of water gradually dripped on their foreheads, begged to be allowed to divulge their secrets.

"A drop of water will pierce the stone."
Ovid

It is speculated that electromagnetic fields may contribute to various ailments, not only individually but also synergistically. The presence of xenobiotics or pathogens in combination with fields or radiation can have unexpected effects that exceed the simple sum of the individual contributions. Speculation has focused on metals and their ions in the body, especially mercury, whether from food, vaccines or dental fillings, or in the case of dentists, cumulative exposure from extractions. Allegations have been made regarding autism, multiple sclerosis and other neurological diseases. Official science considers these assumptions to be refuted or unproven, and the field of the effects of fields and radiation on humans is presented as being under researched. However, let me express my conviction that we will see surprising discoveries in this field.

Author. Antonín Fuksa
Published in StomaTeam 4/2014