Luminance measurement and its distribution
Basic task of measurement, when we research the distribution of photometric value named luminance (cd.m-2). Difference between conventional measurement of luminance and measurement with luminance analyzer stands in obtaining not only visual picture, but also a complex view of luminance distribution in the whole picture. It is not necessary to solve complicated description of the measurement place, in the photograph you see, what was measured and from luminance map you gain values of luminance in any point or area.
Luminance is not dependent on observation distance, but it can be dependent on viewing angle. In every spot the luminance can seem differently at different viewing angle. At the measurement it is advisable to locate the device into the position of supposed observer. Then the device scans the whole scene that is viewed by the observer. Ideal is the use of wide-angle objectives that cover the whole visual field.
Uniformity of luminance, luminance cuts
One of the most frequent indicators at the evaluation of luminance distribution is the uniformity of luminance. Luminances in visual field should not be too low, neither too high in comparison with average value. Of course there have to be some luminance differences that ensures readability and good visibility of observed details. If we explore the luminance on some line, we gain so called luminance cut or profile. It is the progress of the luminance on the line actually, i. e. the progress in concrete direction and coordinate. With LumiDISP you can explore the cuts not only in relative coordinates given in the picture, but after the calculation to angles also in polar coordinates identifying direct orientation in space.
Uniformity of luminance is important for evaluation of road lighting. Into the roads we can involve almost all transportation ways from freeways to foot-paths. Use of luminance analyzer is advisable from several reasons. The most significant is the speed of measurement, when we do not need to reduce the road traffic. At conventional measurement the measurement of one lighting spot could last for hours. At measurement with luminance analyzer it is a matter of seconds. Consequent processing can be performed with computer and you can evaluate necessary indicators. Interesting and indispensable part is the luminance analysis of tunnel lighting, especially the entrance and exit parts.
Lately often discussed question, which is directly related to traffic safety on roads. Properly designed lighting has to ensure sufficient visibility of pedestrians not only on crosswalk, but also in its close neighbourhood. Luminance analysis is in this case generational move in evaluation of lighting, because we can objectively review the visibility of pedestrians at current lighting, but also there can be evaluated the influence of reflectors of coming and oncoming vehicle. Monitored parameters are especially the contrasts of pedestrians and lighted road. They have to be sufficient, so the driver could them in safe time certainly differentiate.
Evaluation of display devices
Into this area we can involve e. g. evaluation of quality of different displays, screens, on-board devices and others. It is also possible to evaluate display devices, such as time-variable traffic signs.
Over the luminance measurement leads the way to other photometric measurements. One of them is the measurement of luminaire lighting intensity. Luminance analyzer is able to measure the distribution of lighting footprint of the luminaire and with specialized algorithms it is able to calculate lighting intensity curves that are basic parameter of the luminaires.
Assessment of light sources
With the technology of luminance analyser it is able to successfully observe even highly intensive luminance of light sources and research the processes, which the conventional luminance meter is not able to register. With the sequential scanning, it is able to record the start of the discharge lamp or to evaluate the changes of the discharge influenced by a change of lamp position. It is possible to measure extreme values of LED luminances, distribution of power in fluorescent tubes and analyse their luminance for reducing of glare.
Luminance contrast occurs when the luminance values of two neighbouring surfaces are different. These two areas must be large enough to be distinguishable and the difference in their luminance must be higher than the minimum value necessary for visual detection. The general assumption is that the observed item with the luminance of La is placed on a certain background with the luminance of Lb. After that, the contract can be calculated using the Weber contrast formula.