Potential resource of mistakes existing while using the modern methods of measurement and calculation in the glare evaluation

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.