Petr Baxant

Unconventional methods of measurement in photometry

The article describes a system of conventional measurements of light intensity curves using standard methods and compares the differences between the goniophotometers used. The article further deals with unconventional methods of measurement of light intensity curves with the help of up-to-date photometers with CCD sensors, describing occurrence of measurement error resulting from short photometric distances.

Operating parameters of luminaires for phytotron

The parameters of luminaires for the phytotron and growth chambers have some characteristics different from conventional luminaires. Example could be the different requirements for spectral distribution, thermal management and requirements for irradiation of plants. This paper deals with the complex description of these requirements on luminaires and they properties, supported by its own laboratory measurements.

Contrast analysis in lighting technology

The paper describes a new approach to the analysis of lighting systems, namely the lighting environment in general, with focus on luminance contrast mapping. Using the modern measuring equipment based on luminance analyzer units it is possible to transmit the obtained data from luminance maps to contrast maps. The current methods of determining contrast are too simple and can be applied only to a limited group of tasks. This paper gives not only the reasons but also suggests a new view of the methodology of evaluating with respect to the physiology of the visual system. This article thus opens a new wave of possible development in the field of light measurement that outperforms the current methods, which do not reflect the technical progress in the field of lighting, and therefore their further use is questionable owing to the exhausted potential.

Static model of LED behaviour depending on operating conditions

Paper presents the static model of the LED behaviour under specific operational conditions created in Simulink tool. This model can be used for different types of LEDs and it operates with commonly available data provided by the manufacturers. Verification of model validity has been performed with high-power white LEDs at two testing methods. First method is based on LED operation with constant supply current and with using of system enabling heatsink temperature regulation. Second method is performed for real conditions operation, ambient temperature is constant and LED control is performed by regulation of supply power. Simulation of multiple LED operation with single heatsink and simulation of LED operation at different ambient temperatures are performed and presented in the paper.

Influence of background luminance on UGR result

The article describes UGR measurement with luminance analyzer and discusses overall impact of background luminance on the calculation result. Background luminance, defined as 2π, causes a problem if the luminance is on the periphery of the visual field. Another complication is that the position index is defined only for the upper half of the view. This causes a complication in glare measurements of luminaires in the lower part of the view. The article attempts to summarize possible variations in luminance analyzer measurements.

Ecodesign of light sources

The aim of this paper is to determine the amount of materials which are used in the light sources construction. Another aim of this paper is to identify environmental demands in the production and disposal of light sources on the basis of the material composition.

Use of photometry in the field of high voltage

Laboratory testing of high voltage tested objects often leads to creation of discharges. Discharges are generated by breakdowns or flashovers outer insulation of the tested objects. These discharges generate emission in the IR, UV and also in the spectrum of light. The spectrum and intensity of radiation is dependent on the duration and level of passing current discharge. The shape, density and the spectrum of the discharge are also to some extent affected by the chemical composition of the gas surroundings, the electrode materials and the atmospheric pressure. The parameters of discharges are usually in HV laboratories specified by the measured time course of voltage and current passing through the discharge. An alternative is using of the analytical tools of lighting laboratory. Timing can be determined by using a fast photodiode. The chemical composition of the gas atmosphere and the electrode material affect the measured spectrum of light and UV. The average measured brightness value is dependent on the passing current of discharge and ambient gas pressure. The content of the article is focused on the application of some instruments from the filed of photometry to the high voltage measurement. This opens up new possibilities for the combination of these two disciplines and finding new possibilities of application.

Growth chamber illumination with a special luminaire

Article describes the design of lighting in growth chamber with low energy consumption. For this purpose we created a special luminaire that allows during different phases of plant life, regulate the spectrum of emitted energy and thereby effectively utilize light without wasting electricity. It is also important light intensity for proper growth of plants, respectively incident radiation. The paper discusses the directional characteristics of the luminaire and its spectral distribution which are an important part of the input data for the design lighting.

Electrical parameters of water at lightning impulse

This paper deals with the description of the behavior of water at lightning impulses. The electric potential distribution in water at lightning impulses is simulated for the calculation of the safe distance. There are not hazardous conditions to human body at distances greater than the safe distance. The examples are swimming pools or water where people are bathing. In these simulations is considered a constant conductivity of the water at impulse current of lightning. But conductivity is not constant value, it change over time and with the instantaneous value of the current passing through. So the main benefit of this article is a description of change in the behavior of the water conductivity.