Modern LED light sources have many advantages, as well as some disadvantages. One of the disadvantages is the pulsating luminous flux, which, in some cases, affects people’s health and well-being negatively. The paper describes the design and making process of a measuring system for determining the quality of LED substitutes for conventional light bulbs and gives an overview of LED light bulbs for household use. The measurement system is controlled using the MATLAB software environment, in which data processing and plotting of the results are also performed. We acquired 59 different LED light bulbs from 37 manufacturers, and performed the measurements. The light bulbs are classified based on the percentage of fluctuations in the luminous flux, and the percentage of deviation of the measured luminous flux compared to the value stated on the packaging by the manufacturer.

In this study, the growth and glucosinolate (GSL) profiles of rocket salad Eruca sativa (Mill.) and Diplotaxis tenuifolia (L.) DC. were determined during 30 days growing under different lighting regimes; T5_ peak at 545 nm, LED1_ peak at 631 nm and LED2_ peak at 598 nm. The biggest increase of dry weight (DW) was measured in E. sativa under T5 (0.657 g DW/plant) and the lowest in D. tenuifolia under LED1 (0.080 g DW/plant). GSL content was found to vary significantly, regardless of the light treatment, but it is related with genotype (E. sativa, r = 0.802**). On average, the highest amount of 4-methylsulfinylbutyl-GSL (glucosativin) (7.3248 mg/g DW) was quantified in E. sativa and D. tenuifolia (6.7428 mg/g DW) under the T5. The regression analysis between different light wavelengths and glucosinolates showed the strongest correlation between photosynthetic photon flux density (PPFD_B) and 4-methylthiobutyl-GSL (glucoerucin) in E. sativa (r = 0.698*) and D. tenuifolia (r = 0.693*), respectively, which indicates the effect of light on the response of plants to induced stress and changes in GSL biosynthesis.

Progress in the development of LED technologies has reached a state which justifies the replacement of lighting with traditional light sources, not only in new buildings but also in existing, older ones. One of such replacements was used as an example of a lighting flicker study presented in this paper. The results of initial measurements indicated that Rapid Voltage Changes (RVCs) are the cause of light flicker. The procedure was introduced and described in this paper to provide the necessary actions to mitigate the light flicker in LED lighting. In order to fulfil this task, the source of locally induced voltage fluctuations has to be identified. A method of identification was developed and a multi-function office printer was identified as the source of RVCs. Using a less sensitive LED driver, changing the connection point of the interfering device, and improving the electrical installation were considered as a set of possible solutions. Laboratory measurements have shown significant sensitivity of the LED driver to RVCs. The identified source of voltage disturbances was confirmed by a simulation of supply voltage variation in the presence of such device in Matlab Simulink with the use of digital flickermeter.

SIQ is, regarding technical regulations in Slovenia, authorized organization for certification of accordance of measuring devices. This is pretentious task and SIQ is performing it fairly well, although there are some instances that require special equipment, which is too expensive for SIQ to afford it. Such cases indicate that we should amend the law in question and allow SIQ to nostrificate the certificates of the foreign authorized institutions - at least the EU ones. One of such test is proof of flickermeter functionality in accordance to IEC 60868-0 and EN 61000-4-15 standards.In Power engineering laboratory at University of Maribor, FERI, we have made some comparative analysis of flickermeter measuring equipment and became aware of noticeable deviation of measuring results. Tests were performed with parallel connected equipment and most of instruments indicate somewhat too high values, therefore we generate series of voltage fluctuation as demand by standard and calibrated the instrument, which has certificate of the German authorized laboratory "Forschungemeinschaft fur Hochspanungs- und Hochstromtechnik E.V." We have checked the level of flicker P-st = 1 and found that the measured values are in accordance with the ones prescribed with the standards. This leads us to conclusion that, regarding to flicker levels in Slovenian network, we have better voltage quality than measured by instruments, attainable in Slovenia.

Electricity distribution networks in densely populated urban areas are, in order to increase the reliability of supply, usually designed as meshed networks, though they always operate in radial configuration. Reconfiguration of distribution networks is achieved through switching operations on switching devices of distribution network branches (switching on/off of a branch). It is often the case that the existing configuration is not the configuration with minimum power losses. With the new computer program, developed by the authors, it is possible to find the network configuration that enables operation with minimum losses. The program proposes the best network configuration to the dispatcher, and the latter makes his own decision whether to change the network configuration or not. The mathematical algorithm for the network reconfiguration is presented in the paper, as well as results of the reconfiguration of the electricity distribution network of the city of Maribor, Slovenia

Interest in building small hydroelectric power plants is growing of late. The problems that occur are mostly caused by the lack of national standards, which should more clearly define the allowed influence of such power stations and their generators on power network voltage distortion. Investors often do not know whether it is necessary to invest in extra equipment for meeting voltage and current quality standards. The authors made some measurements of the influence of very small hydroelectric power stations in the field and in their laboratories, which are described in this paper

Electric arc furnace at " Zelezarna Ravne" steel plant, due to increase of production, causes annoying voltage fluctuation, which appears as disturbed lighting. Paper presents the results of the flicker level measurements and influence of the network reconfiguration in the point of common coupling. Reconfiguration was analysed first with simulation and afterwards in site. Results showing the relation between the short-circuit power and the flicker level are presented.