Acta Polytechnica CTU Proceedings https://doi.org/10.14311/APP.2025.52.0001 Acta Polytechnica CTU Proceedings 52:1–7, 2025 © 2025 The Author(s). Licensed under a CC-BY 4.0 licence Published by the Czech Technical University in Prague INFLUENCE OF VARIOUS ANGLES AND DISTANCES ON LUMINANCE MEASUREMENT RESULTS Jan Bartoníček∗, Tomáš Blodek, Pavel Vrtal Czech Technical University in Prague, Faculty of Transportation Sciences, Konvitská 20, 110 00 Prague 1, Czech Republic ∗ corresponding author: bartoj34@cvut.cz Abstract. The behaviour of drivers in nocturnal conditions is primarily influenced by the early detection of obstacles within the roadway. A reliable approach to evaluate night-time traffic environments is through luminance analysis. This study aimed to investigate the impact of conducting luminance measurements at reduced distances compared to those specified by standard guidelines. Additionally, the study examined the effect of the measurement angle of the luminance analyser on the recorded luminance values. The findings indicate that the measurement angle is a critical factor for ensuring accurate luminance readings, while the distance between the analyser and the measured surface has minimal influence on the results. Statistical analysis confirms that reliable data can be obtained even when deviating from standard measurement conditions. These results suggest that luminance analysis is feasible and applicable across a wide range of traffic scenarios. Keywords: Luminance, lighting, luminance analysis, brightness, luminance analyser. 1. Introduction Addressing traffic safety is a persistent issue that neces- sitates continuous scrutiny. Key strategic documents issued by the European Commission [1], along with national reports [2], indicate that reducing traffic ac- cidents remains a primary priority. When assessing road user behaviour, particular emphasis is placed on the clarity and intelligibility of transport infrastruc- ture [3]. This aspect is crucial not only during the daytime but also in conditions of reduced visibility [3]. Traffic accident statistics reveal that, in 2023, 118 out of 455 fatal accidents in the Czech Republic occurred under low visibility conditions [4]. This figure repre- sents over one-fourth of all fatal accidents recorded that year. These statistics are especially significant considering that traffic volume at night is markedly lower than during daytime hours. The behaviour of drivers in nocturnal conditions is primarily influenced by the early detection of ob- stacles within the roadway. A reliable approach to evaluating nighttime traffic environments is luminance analysis. This method not only assesses the adequacy of illumination in traffic areas but, more importantly, evaluates the visibility and detectability of obstacles or individuals on and around the roadway. The meth- ods for measuring the luminance of specific sections of the traffic area are defined in European and Czech standards, which outline the conditions for conducting these measurements and their subsequent evaluation. The area under consideration is measured over a rela- tively long distance of 60m, determined based on the range of vehicle headlights and the braking distances of vehicles. This measurement is applicable in ideal situations on straight road sections, where ambient luminance is assessed without significant geometric changes in road alignment (both horizontal and verti- cal). However, if a situation arises that necessitates measuring the luminance of the road and its adjacent surroundings in areas with directional curves, the in- vestigator must assess the area at a shorter distance than specified in the standards. The aim of this study is to assess the effect of mea- suring luminance at distances closer than those defined under standard conditions. Additionally, the study aims to evaluate the influence of the measurement angle and the scanning process of the area under con- sideration by the luminance analyser on the resulting luminance values. This analysis seeks to contribute to the optimization of measurements under nocturnal conditions, thereby assisting users in obtaining the most accurate values. 2. Survey of studies on lighting and luminance measurement methods In the field of photometry and luminance measure- ment, numerous studies and research endeavours have addressed various aspects of illumination and its im- pact on traffic safety. Specifically, attention has been directed toward analysing human perception of the environment under different lighting conditions, con- sidering visual adaptation to these scenarios [5]. Con- currently, research has also focused on the influence of external light sources, such as vehicle headlights, assessing how different lighting sources affect the vis- ibility and recognizability of objects. Significant dif- ferences can be observed among halogen, xenon, and LED headlights, as their luminance and technology directly influence the illumination range and light dis- 1 https://doi.org/10.14311/APP.2025.52.0001 https://creativecommons.org/licenses/by/4.0/ https://www.cvut.cz/en J. Bartoníček, T. Blodek, P. Vrtal Acta Polytechnica CTU Proceedings Camera type NIKON D7500 Sensor type CMOS Nikon DX 15.7 × 23.5mm Number of pixels 21.51mil. pixels Image size Large – 5568 × 3712, Medium – 4176 × 2784, Small – 2784 × 1856 Effective number of pixels 20.9 mil. pixels A/D converter 12 bits / 4096 levels, or 14 bits / 16384 levels Shutter speed 1/8000–30 sec. + Bulb ISO sensitivity 100–51200 Table 1. Specification of the LDA camera. tribution. These factors are closely related to the recognizability of objects in the traffic environment. Additionally, the colour of light plays a crucial role in distinguishing individual objects [6]. Object distinctiveness is currently under investiga- tion, particularly at pedestrian crossing points. At these locations, it is crucial to achieve the required lighting intensity, as this directly influences both the luminance and visibility of obstacles. In this context, obstacles are defined as pedestrians moving within the roadway [7]. The employed methods also con- sider the impact of the background, where various distractions or ambient light sources may significantly affect measurement outcomes, potentially leading to the oversight of pedestrians [8]. A study conducted by Seoul National University in the Republic of Korea investigates the influence of traffic area lighting efficiency under adverse weather conditions, such as rain or fog. The findings indicate that distance plays a crucial role in object recogni- tion, which directly impacts the effectiveness of road lighting [9]. Road lighting can be designed dynamically so that the lighting brightness is automated and adjusted based on the speed and intensity of traffic. Such an approach can enhance the efficiency of lighting systems and improve safety in the area [10]. Elements located on the roadway, specifically hori- zontal road markings, are another critical factor that enhances driver orientation in nighttime traffic areas. These road traffic markings convey information re- garding the trajectory of the road, thereby facilitating predictions about its direction and elevation. However, this element is also subject to significant variation, which depends not only on the quality of workmanship but also on the adequacy of ambient lighting [11]. The issue of measuring the luminance of LED lu- minaires using various measuring devices is also ex- amined. Concurrently, the study recommends stan- dardizing the parameters to obtain relevant values. Furthermore, an alternative method for measuring luminance from outside the traffic area is proposed, which may yield comparable results to traditional measurement methods [12]. The study conducted by Aalto University, Finland, focuses on the integration of spatial laser scanning and luminance analysis. By combining the outputs of these measurement instruments, the research fa- cilitates the mapping of illumination in traffic areas and the creation of a spatial representation of lumi- nance [13]. It is important to reference studies that outline methods for conducting nighttime safety inspections, which often involve a significant degree of subjectivity in their evaluations [14]. Additionally, a related con- cern is the uniform distribution of luminance in traffic areas, as it has been shown to be a critical factor in ensuring the safety of road users [15]. Most scientific studies predominantly concentrate on the influence of the surrounding environment and the ways in which users perceive the nocturnal setting. Consequently, the emphasis is primarily placed on the quality of the light source and the subjective per- ception of the night environment. The present study aims to enhance the measurement process and seeks to provide an objective evaluation of the methodology and quality of the data collected. 3. Method of data processing and comparison Experimental measurements of luminance values from different positions were conducted following the de- fined procedure according to ČSN EN 13201 [16]. The basis for the luminance measurement involved defin- ing a grid of measurement points and positioning the measuring device at a predefined location. In general, the measurement area in the longitudinal direction is determined by the distance between luminaires situ- ated in the same row. If there are multiple rows of luminaires in the measured area, the measurement field must be located between the two luminaires in the row with the largest spacing. For measurements with a luminance analyser, the device is positioned 60m in front of the start of the measured area. Ad- ditionally, the height of the centre of the device lens is set to 1.5m above road level, with a measurement angle of 89 ± 0.5°relative to the normal to the road surface. These parameters reflect the observation con- ditions of a driver in a vehicle [16]. The focus of the measurements was the road surface beneath the light source, where the light cone impacting the road was observed. The measurements were conducted using the LDA luminance analyser, with specifications of the LDA settings during the measurements provided in Table 1 [17]. 2 vol. 52/2025 Influence of various angles and distances on luminance . . . Lens type TOKINA 50mm f/1,4 FF Opera for Nikon F Focal length 50mm Aperture range f/1.4–f/16 Filter thread diameter 72mm Table 2. Specification of the LDA lens. Figure 1. Schematic placement of the luminance analyser. The LDA luminance analyser is equipped with a Nikon bayonet mount, allowing compatibility with a wide range of lenses tailored to specific measurement requirements. Table 2 presents the specifications of the lens utilized for the present measurements. The measurement site was selected to ensure safe luminance analysis without the need for traffic restric- tions. The location chosen is a road lighting installa- tion in Studničkova Street, Prague. The light source consists of a high-pressure sodium lamp, which is com- monly used for road lighting. A specific measurement area was defined directly beneath the light source, where the light cone is projected. For the purposes of this study, will be presented only the assessment of measured luminance values from a uniform viewing axis. For the first measurement, the luminance analyser was positioned 60m from the centre of the measure- ment area, with the centre of the analyser’s lens placed at a height of 1.5m above the road surface. In the second measurement, the instrument was positioned 34m away, maintaining the lens at the same height of 1.5m above ground level. This distance was deter- mined with respect to the vehicle’s braking distance under wet road conditions. The third measurement was conducted at a distance of 34m, but with the lens placed at a height of 0.85m above the road surface. This lower height corresponds to a measurement angle aligned with the original measurement specifications, as outlined in ČSN EN 13201. The various positions of the luminance analyser are illustrated in Figure 1. To capture the complete light scene within the mea- surement area, multiple photographs must be taken at varying exposure durations. The exposure times utilized for the measurements conducted with the luminance analyser included 1/2 s, 1 s, 3 s, 5 s, 8 s, and 10 s. The data outputs from the luminance anal- yser are subsequently imported into the LumiDISP software, which calculates and determines the lumi- nance values for each pixel in the photographs. These Figure 2. Luminance image from the first position. Figure 3. Measured luminance values from the first position. luminance images are then merged into a single com- prehensive luminance image, effectively minimizing any overexposed or underexposed areas, Figure 2. In the LumiDISP program, an array was specified to calculate the average luminance value for each designated element within the array. Additionally, the program facilitated the visualization of a graphi- cal waveform illustrating the luminance distribution across a designated strip. This figure can be converted into a tabular format, in which each cell corresponds to the calculated average luminance value for that specific area, Figure 3. 3 J. Bartoníček, T. Blodek, P. Vrtal Acta Polytechnica CTU Proceedings Figure 4. Two-dimensional and three-dimensional display of measured values from the first position. First measurement Figure 2 presents a luminance photograph illustrating the luminance distribution within the measured area of the traffic space. Each pixel is assigned a colour level corresponding to its lu- minance. The colour representation of the luminance photograph may be adjusted according to output re- quirements. The measured luminance values are displayed in Figure 3. For enhanced clarity and interpretation, the measured luminance values have been mapped to a colour scale to depict the effect of the light cone within the measured area. Figure 4 presents both two-dimensional and three- dimensional representations of the luminance distribu- tion within the measured space. The z-axis represents the luminance values, expressed in cdm−2. The fig- ure illustrates the impact of horizontal road markings present in the measured area on the resulting lumi- nance levels. This effect is attributed to the higher re- flectivity of the road markings, which locally increases the brightness by reflecting more of the incident light. To enhance clarity and facilitate comparison, the following measurements are presented in a consistent format. This approach simplifies the identification of differences and similarities between the results and improves the reliability of subsequent analyses. Second measured In this measurement, it is al- ready possible to discern the horizontal road markings, specifically the parking lane. At the same time, a local extreme can be observed that exceeds the measured values in all measurements. This deviation may be caused by a failure to maintain the correct measure- ment angle with the luminance analyser (see Figures 5, 6 and 7). Figure 5. Luminance image from the second position. Figure 6. Measured luminance values from the sec- ond position. Figure 7. Two-dimensional and three-dimensional display of measured values from the second position. 4 vol. 52/2025 Influence of various angles and distances on luminance . . . Third measured This measurement is similar to the second measurement in terms of capturing the overall luminance distribution in the area of interest. However, it provides a more valid measurement in detecting and recording the effect of horizontal road markings on luminance levels (see Figures 8, 9 and 10). 3.1. Comparison of measurements The scatter of all measured luminance values in the study area ranges from 0.6 to 2.0 cdm−2. The Fig- ures 12 and 14 compare the measured values at the location of the luminance analyser with the previ- ously defined parameters. The individual values rep- resent the absolute differences in average luminance attributable to a predefined regular grid of measure- ment points. To enhance clarity, the difference results have been rounded to one decimal place. For accurate correlation and interpretation of the data, the tables should be examined from top to bottom to maintain the measurement direction. Comparisons of the mea- surements were first conducted between the initial and second measurements, followed by comparisons between the initial and third measurements. (1.) First and second measurements The dominant difference was primarily attributed to the horizontal road markings present in the mea- sured area. In other instances, the influence could be ascribed to road geometry or surface conditions. By executing the command to obtain a frequency of 0, a total of 346 cases were identified in the ta- ble where relative agreement existed between the two measurements, while 134 cases demonstrated discrepancies. Subsequently, the command for cal- culating the average value of luminance differences was applied to provide an overall summary. The average value of the absolute differences in aver- age luminance across the entire measured area is recorded as 0.0478 cdm−2 (see Figures 11 and 12). (2.) First and third measurements In this comparison, the presence of horizontal road markings is crucial to the results. A more distinct gap in the roadway extends from the hor- izontal road markings through the measured area. When analysing the measurements, relative agree- ment was found in 408 cases, while discrepancies were observed in 72 instances. The average value of the absolute differences in mean luminance across the entire table representing the measured area cor- responds to 0,0319 cdm−2 (see Figures 13 and 14). 3.2. Summary of verification measurement results The primary factors influencing the results of lumi- nance measurements were predominantly the horizon- tal road markings delineating the parking lane within the measured area. The condition of the roadway, such as the presence of a pothole in the measurement zone, could also impact certain measured values. Occasional Figure 8. Luminance image from the third position. Figure 9. Measured luminance values from the third position. Figure 10. Two-dimensional and three-dimensional display of measured values from the third position. 5 J. Bartoníček, T. Blodek, P. Vrtal Acta Polytechnica CTU Proceedings Figure 11. Comparison of luminance values in three- dimensional display for the first and second measure- ment. Figure 12. Comparison of brightness values in two- dimensional display for the first and second measure- ment. discrepancies in the recorded luminance values may arise from potential inaccuracies in configuring the luminance analyser to the specified parameters for a given measurement. These factors must be consid- ered when interpreting the measured data to ensure the highest accuracy of the results. 4. Discussion During the measurement process and subsequent post- processing, several limitations were identified that may affect the accuracy of the results. The limited number of measurements taken from various direc- tions and angles of the luminance analyser may have reduced variability and, consequently, the reliability of the data. This limitation could be addressed by Figure 13. Comparison of luminance values in three- dimensional display for the first and third measure- ment. Figure 14. Comparison of luminance values in two- dimensional display for the first and third measure- ment. expanding the measurements to encompass additional directions and positions, thereby providing a more comprehensive and precise analysis of the luminance distribution in the traffic area. Furthermore, the de- lineation of the computational areas in the LumiDISP software may have impacted the accuracy of the re- sulting luminance values. To mitigate this issue, it is necessary to accurately synchronize the boundary points of the delineated measurement area in the traffic space with the corresponding boundary points in the delineated calculation area in the LumiDISP software. Additionally, the measurements did not in- corporate detailed information about the light source, which could enhance the thoroughness of the analysis. 6 vol. 52/2025 Influence of various angles and distances on luminance . . . 5. Conclusion Based on the conducted study, it is concluded that the measurement angle is crucial for achieving con- sistent luminance values, while the distance of the analyser is of negligible significance. Statistical analy- sis confirmed that reliable measurement results can be obtained when the correct measurement angle is main- tained. This demonstrates that surface luminance measurements depend primarily on the measurement angle and the angle of incidence, rather than on the distance from the analyser. The validation of the lumi- nance measurements was carried out to enhance safety in traffic areas and to expand the possibilities of its application. This paper also indicates that luminance analysis is feasible even when normative requirements cannot be fully met. While it is essential to base mea- surements on applicable standards, adaptations can be made for specific measurement conditions without significantly impacting the results. References [1] European Commission. White Book. A European transport area for competitive and resource-efficient transport system, Brussels, 2014. [2] Ministry of Transport, Czech Republic. Strategie BESIP 2021–2030 [In Czech; BESIP strategy 2021–2030, 2020. [2024-10-20]. https://besip.cz/Besip/media/ Besip/data/web/Strategie-BESIP-2021-2030.pdf [3] K. Sokanský. Noční bezpečnostní inspekce pozemních komunikací – metodika provádění [In Czech; Night road safety inspection – methodology of implementation]. VŠB – TUO, Ostrava, 2020. 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[17] LDA – Luminance Distribution Analyser: User manual, VUT, Faculty of Electrical Engineering and Communication Technologies, Brno, 2020. 7 https://besip.cz/Besip/media/Besip/data/web/Strategie-BESIP-2021-2030.pdf https://besip.cz/Besip/media/Besip/data/web/Strategie-BESIP-2021-2030.pdf https://www.csorsostrava.cz/metodika/METODIKA%20NO%C4%8CN%C3%8D%20BEZPE%C4%8CNOSTN%C3%8D%20INSPEKCE%201%20VYD%C3%81N%C3%8D%202020.pdf https://www.csorsostrava.cz/metodika/METODIKA%20NO%C4%8CN%C3%8D%20BEZPE%C4%8CNOSTN%C3%8D%20INSPEKCE%201%20VYD%C3%81N%C3%8D%202020.pdf https://www.csorsostrava.cz/metodika/METODIKA%20NO%C4%8CN%C3%8D%20BEZPE%C4%8CNOSTN%C3%8D%20INSPEKCE%201%20VYD%C3%81N%C3%8D%202020.pdf https://www.policie.cz/clanek/statistika-nehodovosti-900835.aspx?q=Y2hudW09Mg%3d%3d https://www.policie.cz/clanek/statistika-nehodovosti-900835.aspx?q=Y2hudW09Mg%3d%3d https://www.policie.cz/clanek/statistika-nehodovosti-900835.aspx?q=Y2hudW09Mg%3d%3d https://doi.org/10.24425/aee.2024.148862 https://doi.org/10.24425/bpasts.2022.143103 https://doi.org/10.3390/app14041595 https://doi.org/10.15199/48.2024.01.42 https://doi.org/10.3390/su13169029 https://doi.org/10.5194/isprs-annals-V-1-2020-199-2020 https://doi.org/10.5194/isprs-annals-V-1-2020-199-2020 https://doi.org/10.1109/EPE61521.2024.10559538 https://doi.org/10.33383/2022-021 Acta Polytechnica CTU Proceedings 52:1–7, 2025 1 Introduction 2 Survey of studies on lighting and luminance measurement methods 3 Method of data processing and comparison 3.1 Comparison of measurements 3.2 Summary of verification measurement results 4 Discussion 5 Conclusion References