Ladislav Kómar

Estimation of Garstang emission function parameters from skyglow monitoring by all-sky camera

A knowledge of an emission function of gound-based light sources is crucial for skyglow modelling. In the case of complex light sources as cities, it is in practice impossible to specify accurately their emission characteristics. Therefore various semi-empirical functions determined by some suitably defined parameters are usually used for description of city light emissions. Assessment of these parameters is obviously extremely difficult. Whether for the complexity of inverse problems of radiative transfer, or for the lack of specialized measurement devices. The aim of the article is to present a simple and effective method of retrieval of city emission function parameters from easily available experimental data. The method is applied on the Garstang emission function because of its generally wide spread utilisation in the light pollution research area. However, it can be in principle applied also on another suitably parametrized emission functions of ground-besed sources. We start from a theoretical model of diffuse radiation intensity distribution over the clear sky, which is based on the successive order of scattering method and which allows relatively simple inverse retrieval of the Garstang parameters. Ratios of zenith radiance to horizontal irradiance at various distances from a source serve as the experimental input data. Such data can be obtained by obvious inexpensive devices what forms the main advantage of the introduced method. In the paper we present utilisation of all-sky cameras which allow simultaneous measurement of the both demanded quantities.

Optics of hemispherical top dome and its effect on tubular light guide efficiency: diffuse light case

To predict the energetic effectiveness of a tubular light guide accurately, a theoretically founded approach has to be used rather than any empirical approximation. The computed illuminance below a light guide can become inaccurate if neither Fresnels equations nor realistic optical path lengths in a cupola are taken into consideration. It is shown that incorporation of both of them into a theoretical model results in lowered luminous flux below the light guide. Assumption of directionally independent transmission coefficient leads to average errors in luminous fluxes of about 10%. The peak errors are typically higher and correspond to lightbeams crossing a hemispherical top dome near its circular base. The solution concept used in this paper can improve predictions of energetic effectiveness for tubular light guides under diffuse daylight conditions.

Submicrometer-sized nonspherical particle separation by laser beam

The radiation pressure exerted on sub-micrometer-size particles is shown to be an important factor predetermining the impact coordinates of the particles after being illuminated by a laser beam. Unlike spherical particles, the nonspherical ones can be deflected perpendicularly to the beam direction if the momentum transfer from the laser beam to a particle is large enough. Such an optical sorting is a useful technology, which can be used to isolate spherules of a specific size from a population of particles of random sizes and shapes. The system of ideal spheres has a wide range of applications in industry and also in the development of targeted optical devices, and so the methods for fast contact-less particle separation are expected to lead to considerable progress in the field. The theoretical model we have developed is demonstrated in a set of numerical experiments on metallic and nonmetallic particles.