This paper presents a detailed analysis of the capabilities of imaging luminance measuring devices for determining discomfort glare. Common opinions on light-emitting diode (LED)-based street lighting luminaires say these products cause high glare. This paper contains the results of calculations and thoughts on the potential measurement errors arising from the incompatibility of the measuring device parameters (number of pixels, sensor dimensions and focal length) to the resolution of the human eye. There are also some cases presented where this incompatibility is of the highest importance, i.e., for the luminance distribution measurements connected with identifying a discomfort glare problem caused, in particular, by multi-source LED luminaires.

Designing, optimizing and analyzing optical systems as part of the implementation process into production of modern luminaires require using advanced simulation and computational methods. The progressive miniaturization of LED (light emitting diode) chips and growth in maximum luminance values, achieving up to 108 cd/m2, require constructing very accurate geometries of reflector and lens systems producing complex luminous intensity distributions while reducing discomfort glare levels. Currently, the design process cannot function without advanced simulation methods. Today’s simulation methods in the lighting technology offer very good results as far as relatively large conventional light sources such as halogen lamps, metal halide lamps and high pressure sodium lamps are concerned. Unfortunately, they often fail in the case of chip-on-board LED light sources whose luminous surface dimensions are increasingly often contained inside a cube of the side length below 1mm. With the high sensitivity of such small chips and lenses with dimensions ranging from a just a few to between 10 and 20 mm, which is presented in this paper, modern luminance distribution measurement methods, luminance modelling and ray tracing methods should be used to minimize any errors arising from incorrectly projecting the design in the final physical model. Also, very importantly, focus should be directed towards reducing a chance of making a mistake while collimating the position of the light source inside the optical system. The paper presents a novel simulation calculation method enriched with an analysis of optical system sensitivity to a light source position. The results of simulation calculations are compared with the results of laboratory measurements for corresponding systems.

Glare prediction is associated with the need to calculate the luminance on the basis of the parameters contained in the IES files or by measuring the luminance distribution of the luminous part of luminaires surface in a given direction. The XXI century is the age of all measurements digitization. This causes the parameters until recently immeasurable become measurable in a relatively simple way. As a result the parameters that we can calculate only in an approximate way, can be measured with very high precision. More and more developed digital measurement technique allows the glare determination on the basis of measurements of luminance distributions using ILMD (Imaging Luminance Measuring Device). The measurement results appear to be relatively accurate for luminaires that are characterised by low luminance gradient variation on the whole surface (luminaires with fluorescent lamps, multi-source luminaires covered with diffuser, etc). The results of the same measurements and calculations may be far from the truth for the harshest variants of luminaires with a single high luminance light source and e.g. multi-source LED luminaires without diffuser. The paper presents selected parameters and problems associated with the correct measurements of the luminance distribution of luminaires in the UGR calculation context.

The last decade is the time of a very dynamic development of lighting technology. This development covers many areas that complement each other. The development of light sources, luminaires, measurement techniques and design methods make it necessary to develop new, effective tools to support the design and analysis of lighting equipment. In lighting technology, the most common analysis is made of such parameters as the illuminance, luminance distribution and discomfort glare, inseparable from the specificity of modern light sources. A characteristic feature of almost all of them is high luminance, on the level of 10 ⁷ - 10 ⁸ cd/m ² . High luminance facilitates the design of very precise optical systems, but also it is strongly associated with the possibility of discomfort associated with glare. Current methods of glare analysis in simulation software are related to conversion to the average luminance value of the luminaire, saved as simplified light parameters in electronic files (IES, LDT or similar). Currently the calculations take place as a result of calculation ratio the value of luminous intensity in a given direction and the surface area of the dimension of the luminaires in the same direction. This can lead to a significant understatement of the luminance of the luminaire in any situation where luminous intensity comes from the heterogeneous luminance distribution on the surface of the luminaire. This situation most often occurs in luminaires with high-luminance light sources with a reflector system and in the case of multi-source luminaires with lenses - eg multi-LED luminaires. The paper presents advanced methods of luminance modelling of light sources developed as a result of digital measurements of luminance distributions. A comparative analysis of the accuracy of the simulation calculations of the analytical lighting fixture model will be presented. The results will be compared to the classic ray tracing methods used in currently used models.

The number of high luminance light sources commonly used in lighting technology is systematically growing, causing an increase in number of potential problems. One of them is the problem of discomfort glare and ways to measure it. Both calculation and measurement methods connected with this parameter have a series of disadvantages and advantages. Among the serious disadvantages, there can be dominant digital “models” of light sources and luminaires, which do not include, practically, any direct information on luminance distribution. To make the measurement results correspond to the calculation results, computer simulations and visual impression of the people assessing the lighting, the measuring devices should correctly record the analyzed parameters. The accurate parameters recording means the situation under which the measurement result is possibly close to what the human eye records. The modern measurement systems, among which there are undoubtedly ILMDs - Imaging luminance measuring devices, are potentially ideal to record all parameters used to calculate glare. Research done by the author proves that especially as far as the small light sources are concerned, such as LEDs and multi-source luminaire systems the parameters of the equipment used have a big influence on the measurement results. Especially, an angular field of view of single pixel of the digital sensor, which relates to a CCD or CMOS sensor size, dimensions of single photo-cell, focal length and technology that is used to make this device (B/W, color). A problem of the influence of depth of field of digital recording equipment with respect to the measured luminance values was dealt with. In this paper and presentation, the relationships of ILMD parameters, such as a field of view of a given type of sensor and single photo-element, including the used lens, will be presented.