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Article

The Photometric Test Distance in Luminance Measurement of Light-Emitting Diodes in Road Lighting

by
Dariusz Czyżewski
Lighting Technology Division, Electrical Power Engineering Institute, Faculty of Electrical Engineering, Warsaw University of Technology, Koszykowa 75, 00-661 Warszawa, Poland
Energies 2023, 16(3), 1199; https://doi.org/10.3390/en16031199
Submission received: 7 December 2022 / Revised: 28 December 2022 / Accepted: 18 January 2023 / Published: 21 January 2023
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Abstract

:
Over the last few years, light-emitting diodes have completely dominated the lighting field. In road lighting, high-power LEDs have replaced traditional light sources. That is why various technical aspects of LEDs have been researched extensively worldwide. However, little research has been conducted in the area of luminance measurement. This paper reviews the methods for measuring the luminance of high-power LEDs. Particular attention is paid to the influence of the measurement distance on the measurement results. Next, the results of the tests using a modern image luminance measuring device (ILMD) for luminance measurements are presented. It is concluded that it is necessary to redefine the photometric test distance. The conducted research demonstrates that an incorrectly selected test distance can lead to the huge errors of several hundred per cent or more. In addition, the possible impact of the incorrect measurements on the design of road lighting installations is presented. It is shown that a road lighting installation can use over 300% more electrical energy compared to the installation based on the correct luminance measurements of single LEDs. In the final stage of the research, the definition of the photometric test distance for LED measurements using ILMD is proposed. The results of the research can also be useful for the luminance measurements of other types of LEDs.

1. Introduction

Light-emitting diodes are among the most popular light sources. LEDs have practically replaced traditional light sources on the market because of their advantages, such as high luminous efficacy [1,2,3], long operating time [4,5], a small size [6], insensitivity to shock, high luminance [7,8,9,10], resistance to low temperatures [11] and easy control [12,13,14,15]. So, in interior lighting, LEDs have replaced fluorescent lamps [16] and in road lighting, they have replaced high-pressure sodium lamps [17,18]. In illumination, LEDs have replaced metal halide lamps [19,20], and in the automotive industry, LEDs have replaced incandescent lamps [21,22], and there are many more such examples.
In addition to the advantages, their other features seem to be important. These features are relatively low luminous flux from a single light-emitting diode [23,24], high luminance (although this is not only an advantage), sensitivity to high-temperature operation [25], and the low power factor of the power supply circuits [26].
That is why many researchers and engineers conduct numerous tests on LEDs, luminaires with LEDs and lighting installations using LED luminaires.
Researchers most often focus on investigating the effect of power supply on photometric and colorimetric parameters, the correct and objective determination of the colour of LED light [27,28,29,30]. They also analyse the reduction in a discomfort glare by LEDs [31,32,33,34,35], the temperature distributions [36,37,38], the system power supply [39,40] and many other aspects. Unfortunately, very few publications are devoted to luminance measurements. There are some articles dealing with the topic of determining luminance distribution in interior lighting [41,42,43]. Such studies make it possible to identify the occurrence of a discomfort glare [44]. In other papers, the researchers focus on assessing luminance distribution in outdoor lighting [45]. Thanks to this kind of measurement, the luminance of light sources and luminaires as well as the background luminance can be determined [46]. A too-high luminance of light sources can create visual discomfort and annoyance for users. Hence, tests of this type can help to identify the occurrence of a discomfort glare. Other tests of this kind make it possible to determine luminance distribution on the road and assess compliance with the standard requirements [47,48]. Including the mesopic vision in the luminance measurements is another interesting aspect of the tests. It is important to note that the mesopic vision appears in road lighting considerations [49,50].
Another topic discussed in the literature is the specific spectral distribution of light-emitting diodes which frequently entails exposing humans to blue light hazards [51,52,53], which affects melatonin suppression [54,55,56] and circadian rhythms [57,58,59,60].
However, very few papers focus on luminance distributions on the surface of light sources and luminaires [61,62,63,64,65], and yet, in the case of light sources, luminance measurements make it possible to determine the luminance distribution on the light-emitting surface. These are the basic tests necessary to design luminaires correctly. In addition, it is important to determine the luminance of the luminaire and its luminance distribution in the surroundings [7,9,66,67]. Performing luminance measurements correctly is a difficult and complex task. On the one hand, this is due to the need to use expensive and complicated measuring equipment. On the other hand, it requires the professional knowledge of how to perform such measurements correctly.
It is important to emphasize that the focus of this paper is the measurement of the luminance distribution on the surface of high-power LEDs used in road lighting luminaires, taking into account different methods of luminance measurement. Regardless of the chosen measurement method, the selection of the correct measurement distance will be an important aspect of measurement accuracy. The determination of the photometric test distance of high-power LED sources in measurements using the image luminance measuring device (ILMD) [68] will be a key point which, unfortunately, has been neglected in the other research conducted so far. The research presented in this article will be used to attempt to define the concept of the photometric test distance in LED measurements using ILMD. In this paper, a manufacturer-calibrated luminance meter was used. The meter had calibration factors set for each lens and the indicated measurement distances. These distances were used in the presented measurements. The ILMD used was verified during other studies [64]. These studies demonstrated the validity of the luminance distributions obtained and were used to create luminance models of the light sources. Therefore, the determination of additional sources of measurement error (e.g., image distortion in the meter lenses, effects of high luminances on neighbouring pixels of the matrix, etc.) was not considered.
The luminance of a light-emitting diode in a given direction can be determined indirectly or directly. Therefore, depending on the method of measurement and the type of the measuring equipment used, three basic measurement methods can be distinguished:
  • The indirect method for measuring luminance;
  • The direct method for measuring luminance using a spot luminance meter;
  • The direct method for luminance measurements using the ILMD (image luminance measuring device).
The indirect luminance measurement method uses the definition of luminance. This method determines the average luminance of a luminous surface in a given direction Lav(C, γ). During the measurement, a radiation detector is placed at a distance r longer than the photometric test distance for determining luminance) from the luminous surface. Then, by reading the current in the detector circuit, the illuminance E at the detector can be determined. Knowing the distance from the light source, the luminous intensity in a given direction can be determined. Then, by calculating the imaginary surface area S (the area seen from a given direction (C, γ)) of the light source, the average luminance of the LED in a given direction can be determined according to relation (1) and Figure 1. The drawing on the left shows the table where the DC power supply and meters are placed. On the right, you can see the goniometer, the mounted light source with the radiator (especially designed cooling system) and the photoelectric cell on the top. More details of this test set-up are presented later in this paper.
L a v ( C , γ ) = E   r 2 d S c o s ( C , γ )   [ c d m 2 ]
In this method, for the measurement to be correct, the distance between the light source and the detector should be such that the photometric distance law can be applied. The idea is that the distance should be sufficient enough to treat the light source as a point. In the case of light sources with Lambertian distribution, the condition is approximately met if the distance in question is five times the length of the light source’s largest dimension. However, it should be emphasised that only the average luminance can be determined in this way. The luminance distribution on the luminous surface of the light source will not be known. Indirect luminance measurement becomes more complicated when the light source is additionally equipped with the optical system of directional reflection, e.g., a parabolic specular reflector. In this case, luminance measurements need be calculated from the distance longer than the photometric test distance. Theoretically, this is the distance from which every point on the optical axis of the luminaire is illuminated by all elementary reflections made on the reflector surface [69]. In this case, the photometric test distance depends on the dimensions of the reflector and a light source [70], and the mean luminance of reflector’s input hole will be determined in the presented way. However, the indirect measurement becomes more complicated in the case of multi-source LED systems (so-called LED arrays). In the literature, there have been several attempts to describe the photometric distance including the far-field description covered in the International Commission on Illumination (CIE) report [71]. However, conducting a laboratory test is recommended to determine the measuring distance properly [72]. At the same time, the average luminance measurement results obtained in this way will be difficult to interpret as it will be problematic to determine the actual luminous surface area. This is because on the LED array, there will be luminances close to the source luminance (the luminance of the reflector or lens surface) and luminances close to zero, i.e., the areas between the mini-reflectors or lenses. Hence, for multi-source systems the indirect method of luminance measurement cannot be used or, rather, using this method can be difficult.
Currently, the direct methods are the main methods for measuring luminance. Historically, the tube luminance meter [73] was the first luminance meter to allow the direct luminance measurement. Today, this is the most basic model of the luminance meter with more educational than practical use. This meter consists of the tube with the internal shutters (with a structure and colour that absorb light), a photometric cell on one side and a shutter (that adjusts the measurement angle of the meter) on the other side. The principle of measurement is to select a small solid angle connected with the light emission (from the surface under test) from the entire half-space in a way that it covers the whole active sur-face of the photocell. The current intensity in the photoelectric cell circuit if is therefore dependent on the luminance of the measured surface L and on the constants of the measuring system, as seen in Formula (2).
i f = c E = c L π d o 2 4 r s 2  
where:
  • c—proportionality factor,
  • do—input hole diameter (a shutter regulating the angle of light coming in),
  • rs—construction constant of the meter (distance from the entrance hole of the meter to the intersection of the light rays inside the meter).
Luminance measurements are based on comparing the value of the measured luminance with in the standard one.
Modern luminance meters work similarly to a tube luminance meter. However, the design of these modern meters is much more complex. They are usually equipped with the complex optics to extend the path of the light rays (in the meter), allowing the luminance of increasingly smaller areas to be measured. In contrast to a tube meter, measurements with modern luminance meters involve comparing the measurement with the luminance of the standard one automatically (the meters are pre-calibrated by the manufacturer). The measurement principle of these meters is also based on selecting a small solid angle connected with the light emission (from the surface under test) from the entire half-space in a way that it covers the whole active surface of the photocell. Theoretically, luminance measurement made using modern meters does not depend on a distance. However, the person taking the measurement sees the entire perspective in the viewfinder of the device (as in a camera) and the area (usually a circle) in which the average luminance measurement is taken (the example of the view in the eyepiece of the meter is shown in Figure 2a). At this point, it is important to make sure that the measurement field (the area of the circle seen through the lens) covers only the area which average luminance is to be determined.
Hence, using modern luminance meters, the limiting photometric distance for measurements is the distance for which the entire measurement field of the meter will be directed at the tested surface. Figure 2a shows the example where the area of a luminous LED source covers approximately 25% of the measuring field (the measurement field is a black circle on white LED housing). In this case, if the area outside the light source is unlit, the meter readings will be lower by 75%. Figure 2b shows a correctly selected measuring distance where the measuring field only covers the surface of the light source (the measurement field is a black circle on the inner ring white LED housing). Then, the result will be correct, and the average luminance of the tested LED can be correctly determined. It is worth mentioning that there are traditional luminance meters that allow for setting different sizes (angles) of the measuring area (different diameters of the measuring location (circle) seen in the lens by the observer). It is then easier to adjust the distance so that the measuring field covers the entire area in which the average luminance is to be measured. In addition, if the meter allows for setting a sufficiently small measuring field, the distribution of luminance can be determined in a simpler way. It can be achieved by dividing, for example, the LED surface into nine areas and the spot luminance can be measured in the centre of each area.
Matrix luminance meters (ILMDs) offer the most efficient measurement possibilities. ILMDs were developed during the process of developing digital cameras. The optical system (lens), the correction filter (V(λ) adjustment), the sensor (photosensitive matrix) and the image sensor are the key elements of ILMDs. The optical system consists of several or even more than a dozen lenses which task is to project a sharp image onto a photosensitive matrix (CCD or CMOS) without any distortions or interference. The ILMD has the advantage of being able to work with multiple lenses (which requires a separate calibration process). This makes it possible, for example, to analyse the luminance distribution in large areas such as street lighting [74,75,76,77] and with different lens to analyse the luminance distribution on a very small LED area [7,62,78].
Based on the review of the studies of the luminance photometry, an urgent need has arisen to determine the distance from which luminance on the surface of a light source or a luminaire can be correctly determined. Incorrectly measured luminance can lead to poorly designed luminaire optics and, consequently, to incorrect lighting designs. It can also result in false glare evaluation from luminaires [79,80]. This issue is addressed in this paper, as well as the determination of the distance from which high-power LEDs should be tested in practical measurements. This research will, of course, also be relevant for other measurements using ILMDs. Figure 3 illustrates the relevance of the discussed problem. On the left image, the measurement range has been manually selected and the luminance distribution along the road can be seen. On the right image, the ILMD automatically adjusted the measurement range to the maximum luminance. According to this measurement, the luminance of light sources where luminance distribution is oriented by the lenses, is several thousand cd/m2. Of course, this result is significantly lower than the correct result.

2. Materials and Methods

The research was carried out in a photometric darkroom at a technical university in the European Union. A high-precision measuring set-up, shown in Figure 4, was used to conduct tests to determine the photometric distance of high-power LEDs. This set-up allowed measurements at distances of up to 1 m. The main component of the stand was a goniophotometer (1), which allowed for the fixing of the specially designed cooling system (2) in the form of a heat sink and tested high-power LEDs (3). Before the measurements, the LEDs were positioned using two lasers (4) and two-micrometre screws (5) placed on a measuring table (6). The goniophotometer allowed high-power LEDs to be tested in the system (C,γ). It also allowed the photometric distance to be changed as it was possible to move the luminance meter (7) up and down. The diodes were powered by the programmable DC power supply PPS 3210 (Motech) (8), and the electrical parameters were controlled with two laboratory multimeters (9), one acting as a voltmeter and the other as an ammeter. The thermal conditions of the LEDs were controlled using an Appia 5510 temperature meter (10). Direct luminance measurements were made with the LMK98-3 Color Techno Team luminance, colour measuring camera (7) and interchangeable lenses (11). Micro and 50 mm lenses were used in the measurements. Each was fitted with grey filters to reduce the luminance of the high-power LEDs to the level that could be recorded directly by the luminance meter. For measurement distances above 1 m, the test set-up shown in Figure 5 was used. It was equipped with a larger goniometer which also made the tests of the high-power LEDs in the (C, γ) system possible. This set-up made it possible to place an ILMD on the special stand and on the same axis with a goniometer and it allowed the meter to be moved over distances greater than 1 m.
Technical parameters of the LMK98-3 luminance meter are provided in Table 1.
The measuring set-up presented in Figure 5 was used for distances above 1 m.
Before each measurement, the diodes were illuminated until thermal stability was reached, which was monitored during the measurements.
Three high-power LEDs from different manufacturers were selected for this test. The main criteria were that the light sources should be popular, widely available and currently used in road lighting luminaires. The selected light-emitting diodes varied in size and photometric and electrical parameters (luminous flux, rated current, voltage and power). Luminance distribution of all the high-power LEDs selected for testing was close to the Lambert distribution. When choosing the high-power LEDs for testing, it was important to make sure that the photometric parameters were stable during measurements. Two LEDs (LED1 and LED2) were fitted with primary optics.
Table 2 shows the most important technical parameters of the high-power LEDs selected for testing and ranked in terms of power rating.
The tests were carried out for single LEDs and the modules consisting of 4 or 16 LEDs. The measurements were conducted for the following different photometric distances: 180 mm, 280 mm, 306 mm, 370 mm, 486 mm, 655 mm, 818 mm and 940 mm. They were made using the set-up for precise measurements which is shown in Figure 4. The rest of the measurements were carried out for distances: 1354 mm, 3778 mm, 8049 mm and 11,465 mm. They were made on the second measurement set-up shown in Figure 5. For LED1 and LED2, the supply currents were 0.7 A, while the LED current was 0.6 A.

3. Results

The first essential step of the study was to determine and analyse the luminance distribution from the direction of the optical axis from as close distance as possible. For this purpose, a macro lens was used where the photometric distance was 180 mm. As the result of the measurements, changes in mean luminance and maximum luminance were determined for the various areas marked on the tested LEDs. The areas marked for analysis covered 0.5%–1%–5%–10%–25%–50%–75%–100% of the luminous area of the LEDs, respectively, as shown in Figure 6. The centre of the marked regions was at the geometric centre of the individual LEDs. Thanks to this analysis, it was possible to determine in which area the maximum luminance of the LED is located and whether this area is the smallest (of those analysed) and closest to the geometric centre of the LED, i.e., the most relevant from the point of view of optical system design.
In the next stage of the research, the effect of the supply current on the luminance distribution of the tested LEDs was checked. In this case, no effect of supply current on the luminance distribution on the LED surface was found. However, a change in luminance levels was found:
  • For LED1 for a maximum supply current of 2.0 A, the maximum luminance value increased to 49.1 Mcd/m2. The tested LED was mounted in the module consisting of 16 LEDs;
  • For LED2 for a maximum supply current of 1.8 A, the maximum luminance value increased to 76 Mcd/m2. Similarly to LED1, the tested LED2 was mounted in the module consisting of 16 LEDs;
  • For LED3 for a maximum supply current of 1.0 A, the maximum luminance value increased to 24.8 Mcd/m2. The tested LED was mounted in the module consisting of 4 LEDs.
The main objective of the research was to determine the effect of the photometric distance on luminance distribution and luminance levels for the selected high-power LEDs. LED2, the light source with the smallest dimensions, was chosen for the graphical presentation of the measurement results. The results of the measurements are presented in Figure 7. The right-hand figure shows the magnified picture of luminance distribution. In contrast, the left-hand figure shows the size of LED2 across the whole CCD matrix of the luminance meter. This way of presenting the results allowed a preliminary assessment of the size of the light source in relation to the whole image recorded by the ILMD. The matrix of 16 LED2s was tested. This allowed for a similar temperature distribution as in road lighting luminaires where such modules are used. The LEDs were placed 30 mm apart horizontally from each other and 20 mm apart vertically from each other. Figure 7 shows only one LED for distances from 180 mm to 370 mm. Six LEDs were visible for distances from 486 mm to 655 mm. Twelve LEDs were visible for distances of 818 mm, while all sixteen LEDs were visible from 940 mm to 11,465 mm. In Figure 7, the left images show the view recorded by the entire array. The right image, however, shows a magnification of the measured LED. In this way, it is possible to see how the number of pixels onto which the image is projected changes and how the image deformation (pixelation) progresses. This can be particularly seen for the largest distance of 11,465 mm—the last right image.

4. Discussion

According to the assumptions made, the initial stage of the research was to determine the luminance from the direction of the optical axis from as close distance as possible. The measurement results and their analysis are summarised in Table 3. Measurement areas are shown in Figure 6.
By analysing the luminance distributions on the LED surface (shown in Figure 6), it can be seen that they are not uniform. The luminance image is more ordered on LED3, which lacked the original optical system. Hence, it can be concluded that the original optical system can influence the non-uniformity of the luminance distribution. On the surface of LED3, eight micro-chips with luminance close to the maximum luminance can be distinguished.
From the tests summarised in Table 3, it can be seen that in none of the LEDs tested is the maximum luminance found in the centre of the LED or even in the area closest to the centre (area number 8). In the case of LED1, the maximum luminance occurs in the area number 6. In LED2 and LED3, the maximum luminance occurs in the area number 4.
For LED1 and LED2, it was found that the larger the test area, the lower the average luminance. This is due to the lack of many micro-LEDs on the luminous surface and the temperature distribution conditions on the LED surface. The situation is different for LED3. The way the microchip is distributed determines the formation of local luminance maxima. Hence, the average luminance increases from an area number 1 to an area number 3 (where it reaches its highest value) and then decreases from an area number 3 to an area number 8.
The disparity between the maximum luminance and the average luminance measured for the entire LED area (area no. 1) ranges from less than 80% for LED2 to around 60% for LED1 and LED3.
The next stage of the analysis was to determine the effect of photometric distance on the distribution and luminance levels for the high-power LEDs selected for the test. The measurement results with their analysis are summarised in Table 4 for LED2.
The first column of Table 4 shows the distances from which the luminance was measured on the surface of the LEDs selected for the presentation. The second and third columns present the results of the maximum and average luminance measured on the LEDs’ surface for a given photometric distance. The fourth column lists the number of pixels covered by the image of the measured LED for a given measurement distance. The next columns contain calculations, where the result obtained for a distance of 180 mm is the reference. For example, in the second row of results, in the fifth column, the maximum luminance measured for a distance of 280 mm was divided by the maximum reference luminance, i.e., that measured for 180 mm. Then it was multiplied by 100 to give the result in percentage. In the last column, the results were multiplied by 1000 to get the result in the per mil.
The results are summarised in Figure 8 for the maximum luminance to facilitate the analysis of how the image size (expressed in the number of pixels) changes with changing measurement distance for individual LEDs.
Analysing the obtained results presented in Table 4 and Figure 8, it can be concluded that the maximum luminance changes with the measurement distance. It was observed that the higher the measurement distance, the lower the number of pixels forming the LED image on the ILMD and the lower the value of the read maximum luminance. Taking the maximum luminance read from the nearest photometric distance as a reference, it can be noticed that at least 99% of this luminance was obtained for:
  • LED1 for a distance of 370 mm, where the image size was less than 5900 px;
  • LED 2 for none of the distances greater than 180 mm measurement distance. It was estimated that the image should be at least 25,000 px in size;
  • LED 3 for none of the distances greater than 180 mm. It was estimated that the image should be at least 40,000 px in size.
From the analysis, it was determined that for the maximum luminance to be at 99% of the maximum luminance obtained for the most accurate measurement for all LEDs, the size of the LED image should cover at least 40,000 px.
It was also determined that at least 90% of the percentage of maximum luminance was obtained for:
  • LED1 for a distance of 1354 mm, where the image size was less than 333 px;
  • LED2 for a distance of 486 mm, where the image size was less than 2701 px;
  • LED3 at a distance of 818 mm, where the image size was less than 2177 px.
The analysis shows that for the maximum luminance to be at 90% of the maximum luminance obtained for the most accurate measurement for all LEDs, the size of the LED image should cover at least 3000 px.
The results are summarised in Figure 9 for the average luminance to facilitate the analysis of how the image size (expressed in the number of pixels) changes with changing measurement distance for individual LEDs.
As in the previous case, analysing the obtained results presented in Table 4 and Figure 9, it can be concluded that the average luminance changes with the measurement distance. It was observed that the higher the measurement distance, the lower the number of pixels forming the LED image on the matrix of the ILMD meter and the lower the value of the read average luminance. Taking the average luminance read from the nearest photometric distance as a reference, it can be seen that at least 99% of this luminance was obtained for:
  • LED1 for a distance of 280 mm, where the image size was 12,970 px;
  • LED2 for a distance of 280 mm, where the image size was 8925 px;
  • LED3 for a distance of 306 mm, where the image size was 26,610 px.
The analysis shows that for the average luminance to be at 99% of the average luminance obtained for the most accurate measurement for all LEDs, the size of the LED image should cover at least 20,000 px (estimated from Figure 9).
Furthermore, it was determined that at least 90% per cent of the average luminance was obtained for:
  • LED1 for a distance of 486 mm, where the image size was just under 2881 px;
  • LED2 at a distance of 486 mm, where the image was less than 2701 px;
  • LED3 at a distance of 655 mm, where the image size was less than 3481 px.
The analysis shows that for the average luminance to be at 90% of the mean luminance obtained for the most accurate measurement for all LEDs, the size of the LED image should cover at least 3000 px (estimated from Figure 9).
The luminance characteristics of LEDs are the fundamental set of information used in the design of the luminaire optic. Thus, if the shown differences in luminance levels were used for photometric calculations of road lighting, the fundamentally different calculation results for road lighting designs would be obtained.
It was therefore decided to analyse how the incorrectly chosen luminance measurement distance could affect the energy efficiency of road lighting. This type of analysis results from the fact that all tested LEDs were from road lighting luminaires produced by the recognised manufacturers.
A dual-carriageway expressway with three lanes and the width of 11.25 m of each carriageway was chosen for the analysis. The calculations assumed luminance coefficient qo = 0.07 and a maintenance factor of 0.8. A luminaire from the recognised manufacturer was selected with one of the tested LEDs. The specifications of the luminaire are summarised in Table 5. Lighting class M2 [81] was assumed for each of the two carriageways. The centre lane was 2 m wide. Double sided staggered layout of luminaires was assumed. It was also assumed that the number of lighting hours for the luminaires would be 4200 h per year. The simulation calculations used the definitional term luminance, i.e., the relationship between luminance and luminosity (LID) in a given direction.
Certain limits were adopted in the placement of luminaires. These are summarised in Table 6.
Five cases were considered in the analysis. In the first reference case, the luminance distribution on the LED2 surface (mounted in the luminaire) was measured from a distance of 280 mm. This fact ensured that the photometric data of the luminaire were consistent with the manufacturer’s catalogue data. In other cases, photometric distances of 306 mm, 486 mm, 1354 mm and 3778 mm were adopted, which resulted in the lowering of the luminaire’s lighting performance. The results of the analysis are summarised in Table 7.
The first column of Table 7 presents the distances at which the LEDs used in the road luminaire described in Table 5 were measured. The second column gives the luminaire spacing parameters in the spacing (S) [m]/luminaire height (H) [m]/inclination angle (Q) [°]/overhang (OH) [m] convention, according to the ranges defined in Table 5. The luminaires were placed in such a way as to ensure the highest energy efficiency of the given lighting installation. The third column shows the calculated power density indicator (Dp). The annual energy consumption indicator (De) was calculated in the fourth column. The fifth column gives the power of the installation that illuminates two carriageways over a length of 10 km. The last column shows the energy consumed by the lighting installation for one year.
Using the data collected in Table 7, the energy consumed to illuminate a 10-km road section stretch was determined for a given LED photometric distance and luminaire arrangement. The results are shown in Figure 10.
In Figure 10, as previously presented, it was assumed that the reference energy consumption would be for an LED photometric distance of 280 mm. The energy consumption thus calculated to illuminate 10-km road section was considered to be the reference value (100%). Hence, it can be concluded that an increase in the luminance photometric distance of the individual LEDs used in the luminaire increases the electricity consumption and decreases the energy efficiency of that lighting installation. For a photometric distance of 306 mm, an increase in electricity consumption was 1.7% compared to the reference installation (280 mm). A further rise in the photometric distance to the value of 486 mm increased energy consumption by 5.7%. The further increases in the photometric distance for individual LEDs resulted in the increased electricity consumption. For a distance of 1354 mm, the increase was 38.6%; for a distance of 3778 mm, the increase was already 58%; and for a distance of 8049 mm, the growth was as high as 306.3%.
Based on the presented test results, the following analysis can be conducted. Increasing the photometric distance of individual LEDs to 3778 mm resulted in a 42.5% decrease in the average luminance over the LED area (according to Table 4). If, on the basis of these results, the luminaires were designed and located to illuminate 10 km of dual carriageway (on the basis of these results), this would result in an increase in electricity consumption of more than 306%.
Analysing Figure 10, it can be seen that the way the luminance of individual LEDs in luminaires is measured can directly affect the energy efficiency of road lighting. Increasing the luminance photometric distance of the LEDs increased electricity consumption for a lighting installation using the previously measured LEDs.
It needs to be highlighted that errors in luminance distribution measurements should be identified at the level of additional verification measurements such as measurement of luminous flux or LID.

5. Conclusions

In this paper the reviews of the methods for measuring luminance on the surface of high-power LEDs are presented. However, these research results can also be useful for other luminance measurements. The correct and accurate measurement methodology for indirect and direct methods using a classic luminance meter is shown. For these methods, the photometric distance for luminance measurements is defined.
However, this study focuses on the practical measurements of luminance distribution using a modern matrix luminance meter. In the case of the ILMD meter, it has been found that the photometric distance influences the results of the measured luminance levels on the surface of high-power LEDs. Too big photometric distance lowered the maximum and the average luminance results in relation to the reference results. Since in the literature there is no definition for the photometric distance for luminance measurements using the ILMD meter, it has been decided to propose the following definition:
The photometric test distance for luminance measurements with the ILMD meter is the distance from which the measured image is projected onto a sufficient number of pixels of the photosensitive matrix to ensure that the luminance meter readings are constant and repetitive.
The proposed definition considers only the aspect of photometric distance. Other possible measurement errors (e.g., distortion of the image by the meter lens) are not included in this definition.
If the image is too small after passing through the optical system of the luminance meter, the local maxima may not be visible. The obtained image may not cover all the pixels on the photosensitive matrix and this image is averaged over these extreme pixels. In this case, significant deviations of up to several hundred per cent can occur in the luminance meter readings.
The conducted tests have shown that reducing the luminance measurement distance should be the focus of luminance measurements. In this way, the measured object will form the image which will cover as many pixels of the ILMD meter matrix as possible. The developed approach ensures the accurate luminance measurement. This approach is in contrast to luminous intensity measurements where the distance should be longer to obtain correct results.
According to the conducted research, it was found that the luminance distribution on the surface of high-power LEDs used in road lighting is not uniform. It has been shown that in none of the tested LEDs, the maximum luminance is in the centre of the LED or even in the area closest to the centre. Designers of the optical systems should take into consideration this fact. In addition, it was discovered that the LED driving current does not affect the luminance distribution on the LED surface. In this case only the luminance level changes.
Based on the tests and their analysis, it was determined that for the maximum luminance to be at 99% of the maximum luminance obtained for the most accurate measurement for all LEDs, the LED image size should cover at least 40,000 pixels. In the case of the average luminance, it was determined that for the average luminance to be at 99% of the average luminance obtained for the most accurate measurement for all LEDs, the size of the LED image should cover at least 20,000 pixels. The obtained results were for a monochrome matrix. For matrices with Bayer filters, the number of pixels needs to be increased proportionally.
Since the whole analysis was conducted for non-uniform luminance distributions how the photometric distance would affect the luminance measurements for a source with uniform luminance was also analysed. For this purpose, the luminance standard was measured from different distances. In this case, the effect of the photometry distance on the luminance measurement results was also discovered. These results support the validity of the conducted research and the proposed definition of the photometric test distance.
The incorrect results of the luminance distribution on the LED surface may increase the energy consumption of the lighting installation. It is therefore recommended to verify the luminaire parameters by determining the luminance distribution and/or the luminous flux of the luminaire. This will allow incorrect LED luminance models to be eliminated at the early stage of the production process.
The high measurement accuracy is guaranteed only by the measurements of the luminance distributions from a distance ensuring an adequate image size on the ILMD matrix.
Hence, final recommendations have been made:
  • The image of the investigated LEDs on the ILMD CCD should be as big as possible;
  • Measurements from a long distance with a large focal length lens are the ideal solution;
  • It is best to measure each LED separately in a multi-source LED module;
  • Incorrectly determined luminance of the light source may influence incorrect designs of luminaire optics. That is why other verification measurements (e.g., luminous flux or LID) are recommended.
The presented test results have confirmed the considerable measurement possibilities of ILMD meters. The possibility to measure luminance level and its uniformity simultaneously is particularly convenient and valuable. At the same time, the test results have showed that good knowledge and experience of the person performing the measurements are necessary to make luminance measurements correctly. During measurements, it is essential to remember about the influence of the photometric distance on the reliability of the test results. A lack of this knowledge can lead to significant measurement errors.
Further research will be devoted to examining how the photometric distance of LEDs affects the correctness of luminance measurements that determine glare reduction in road lighting. In addition, the aspects concerning the impact of other measurement errors on the luminance distribution results are planned to be researched further.

Funding

This research received no external funding.

Data Availability Statement

Not applicable.

Acknowledgments

The author would like to express his gratitude to Signify Poland for covering the cost of publishing the research results.

Conflicts of Interest

The author declares no conflict of interest.

References

  1. Zhou, Z.; Wang, H.; Zhang, J.; Su, J.; Ge, P. LED chip-on-board package with high colour rendering index and high luminous efficacy. Light. Res. Technol. 2018, 50, 482–488. [Google Scholar] [CrossRef]
  2. Ramos-Romero, I.R.R.-R.; Moreno, I. Light spectrum for maximum luminous efficacy of radiation and high color quality. In Current Developments in Lens Design and Optical Engineering XIX; SPIE: Bellingham, WA, USA, 2018. [Google Scholar]
  3. Tao, X.-H.; Yang, Y. Theoretical Modeling of Luminous Efficacy for High-Power White Light-Emitting Diodes. Chin. Phys. Lett. 2017, 34, 38501. [Google Scholar] [CrossRef]
  4. Padmasali, A.N.; Kini, S.G. A Lifetime Performance Analysis of LED Luminaires under Real-Operation Profiles. IEEE Trans. Electron Devices 2020, 67, 146–153. [Google Scholar] [CrossRef]
  5. Richter, J.L.; Tähkämö, L.; Dalhammar, C. Trade-offs with longer lifetimes? The case of LED lamps considering product development and energy contexts. J. Clean. Prod. 2019, 226, 195–209. [Google Scholar] [CrossRef]
  6. Chen, W.-R.; Luo, Y.-S. A Screen Method for the Mass-Production of the Small-Size and Side-View LED Package. Crystals 2018, 8, 350. [Google Scholar] [CrossRef] [Green Version]
  7. Słomiński, S. Selected problems in modern methods of luminance measurement of multisource led luminaires. Light Eng. 2016, 1, 45–50. [Google Scholar]
  8. Chaves, J.; Falicoff, W.; Benitez, P.; Miñano, J.C.; Parkyn, W.A.; Dross, O. Luminance enhancement of LED light sources for etendue-limited applications. In Proceedings of the Nonimaging Optics and Efficient Illumination Systems III, San Diego, CA, USA, 13–17 August 2006. [Google Scholar]
  9. Czyżewski, D. Comparison of luminance distribution on the lighting surface of power LEDs. Photon-Lett. Pol. 2019, 11, 118–120. [Google Scholar] [CrossRef]
  10. Han, H.-S.; Qi, A.-X.; Liu, J.-G.; Xie, X.-B.; Sun, S.-L. Application of Micro-LED technology in airborne display. Chin. J. Liq. Cryst. Disp. 2021, 36, 439–447. [Google Scholar] [CrossRef]
  11. Czyzewski, D. Luminance distribution of LED luminous surface. Prz. Elektrotech. 2010, 86, 166–169. [Google Scholar]
  12. Bunjongjit, S.; Ananwattanaporn, S.; Ngaopitakkul, A.; Jettanasen, C.; Patcharoen, T. Design and Application of Daylight-Based Lighting Controller on LED Luminaire. Appl. Sci. 2020, 10, 3415. [Google Scholar] [CrossRef]
  13. Ji, H.; Zhao, Q.; Wang, X.; Sun, Q. ZigBee-based LED intelligent lighting control system. In Proceedings of the 2013 10th China International Forum on Solid State Lighting, Beijing, China, 10–12 November 2013. [Google Scholar]
  14. Khatavkar, N.; Naik, A.A.; Kadam, B. Energy efficient street light controller for smart cities. In Proceedings of the 2017 International Conference on Microelectronic Devices, Circuits and Systems, ICMDCS, Vellore, India, 10–12 August 2017. [Google Scholar]
  15. Khorgade, M.; Jaiswal, A.; Karmore, M.; Kamble, V. Smart Street Light. Int. J. Adv. Res. Sci. Commun. Technol. 2021, 6, 152–154. [Google Scholar] [CrossRef]
  16. Tan, C.H.; Choong, F.C.M.; Teo, Y.C.; Lin, Y.; Ho, K.C. Power optimization in hybrid Visible Light Communication for indoor applications. In Proceedings of the 2016 Progress in Electromagnetics Research Symposium, PIERS, Shanghai, China, 8–11 August 2016. [Google Scholar]
  17. Ylinen, A.M.; Puolakka, M.; Halonen, L.; Bizjak, G. Road lighting in change—Towards better energy-efficiency in Finland. Light Eng. 2012, 20, 89–95. [Google Scholar]
  18. Czyżewski, D. The street lighting luminaires with LEDs. Prz. Elektrotech. 2009, 86, 283–288. [Google Scholar]
  19. Hermoso-Orzáez, M.; Rojas-Sola, J.; Calderón, A.G. Electrical consequences of large-scale replacement of metal halide by LED luminaires. Light. Res. Technol. 2018, 50, 282–293. [Google Scholar] [CrossRef]
  20. Krupiński, R. Simulation and Analysis of Floodlighting Based on 3D Computer Graphics. Energies 2021, 14, 1042. [Google Scholar] [CrossRef]
  21. Jiao, J.; Wang, B. Etendue concerns for automotive headlamps using white LEDs. In Proceedings of the 3rd International Conference on Solid State Lighting, San Diego, CA, USA, 3–8 August 2003. [Google Scholar] [CrossRef]
  22. Kovalenko, O.Y.; Zhuravlyova, Y.A. Analysis of Characteristics of Halogen and LED Automobile Lamps. Light Eng. 2020, 28, 57–62. [Google Scholar] [CrossRef]
  23. Raypah, M.E.; Sodipo, B.K.; Devarajan, M.; Sulaiman, F. Estimation of Luminous Flux and Luminous Efficacy of Low-Power SMD LED as a Function of Injection Current and Ambient Temperature. IEEE Trans. Electron Devices 2016, 63, 2790–2795. [Google Scholar] [CrossRef]
  24. Cao, Y.; Yuan, W.; Chen, W.; Li, M.; Fan, J.; Zhang, G. Predicting of luminous flux for a LED array using artificial neural network. In Proceedings of the 2020 21st International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, EuroSimE, Cracow, Poland, 5–8 July 2020. [Google Scholar]
  25. Xiao, Y.; Zhao, Y.; Yang, Y.; Gao, S.; Han, S.; Yang, P. Effects of multi-factors on the junction temperature of LED automotive lamp chips. Microelectron. Reliab. 2022, 136, 114658. [Google Scholar] [CrossRef]
  26. Adoghe, A.U.; Eberechukwu, O.C.; Sanni, T.F. The effect of low power factor led lamp invasion on the utility grid: A case study of Nigerian market. In Proceedings of the 2017 IEEE PES PowerAfrica, Accra, Ghana, 27–30 June 2017. [Google Scholar]
  27. Raggiunto, S.; Belli, A.; Palma, L.; Ceregioli, P.; Gattari, M.; Pierleoni, P. An Efficient Method for LED Light Sources Characterization. Electronics 2019, 8, 1089. [Google Scholar] [CrossRef] [Green Version]
  28. Supronowicz, R.; Fan, J.; Listowski, M.; Watras, A.; Fryc, I. Application of different metrics for describing light color quality of white LED. Photon-Lett. Pol. 2021, 13, 31–33. [Google Scholar] [CrossRef]
  29. Mozyrska, D.; Wyrwas, M.; Fryc, I. The determination of the LEDs colorimetric parameters, in the range of their operating temperature. Prz. Elektrotechniczny 2012, 93, 232–234. [Google Scholar]
  30. Kowalska, J. Colour rendition quality of typical fluorescent lamps determined by CIE Colour Fidelity Index and Colour Rendering Index. Prz. Elektrotechniczny 2019, 95, 94–97. [Google Scholar] [CrossRef]
  31. Stanke, L.; Viktorová, L.; Dominik, T. Discomfort Glare Perception by Drivers—Establishing a Link between Subjective and Psychophysiological Assessment. Appl. Sci. 2022, 12, 3847. [Google Scholar] [CrossRef]
  32. Yang, Y.; Luo, R.M.; Huang, W. Assessing glare, Part 3: Glare sources having different colours. Light. Res. Technol. 2018, 50, 596–615. [Google Scholar] [CrossRef]
  33. Geerdinck, L.; Van Gheluwe, J.; Vissenberg, M. Discomfort glare perception of non-uniform light sources in an office setting. J. Environ. Psychol. 2014, 39, 5–13. [Google Scholar] [CrossRef]
  34. Huang, W.; Yang, Y.; Luo, M.R. Discomfort glare caused by white LEDs having different spectral power distributions. Light. Res. Technol. 2018, 50, 921–936. [Google Scholar] [CrossRef]
  35. CIE 232:2019; Discomfort Caused by Glare from Luminaires with a Non-Uniform Source Luminance. CIE: Vienna, Austria, 2019.
  36. Różowicz, A.; Wachta, H.; Baran, K.; Leśko, M.; Różowicz, S. Arrangement of LEDs and Their Impact on Thermal Operating Conditions in High-Power Luminaires. Energies 2022, 15, 8142. [Google Scholar] [CrossRef]
  37. Li, C.; Chen, Z.; Jiao, F.; Zhan, J.; Chen, Y.; Chen, Y.; Nie, J.; Zhao, T.; Kang, X.; Feng, S.; et al. Effects of interfaces and current spreading on the thermal transport of micro-LEDs for kA-per-square-cm current injection levels. RSC Adv. 2019, 9, 24203–24211. [Google Scholar] [CrossRef] [Green Version]
  38. Mukherjee, A.; Soni, A.; Gupta, M. LED driver design and thermal management. In Lecture Notes in Electrical Engineering; Springer: Berlin/Heidelberg, Germany, 2020. [Google Scholar]
  39. Farcas, C.; Petreus, D. LED Driver with BOOST-BUCK Topology. In Proceedings of the 2021 44th International Spring Seminar on Electronics Technology (ISSE), Bautzen, Germany, 5–9 May 2021. [Google Scholar]
  40. Pang, Z.; Cai, Z. Research on digital long-life time LED driver. Optik 2021, 239, 166797. [Google Scholar] [CrossRef]
  41. Suk, J.Y. Luminance and vertical eye illuminance thresholds for occupants’ visual comfort in daylit office environments. Build. Environ. 2019, 148, 107–115. [Google Scholar] [CrossRef]
  42. Sielachowska, M.; Tyniecki, D.; Zajkowski, M. Luminance distribution measurements in a classroom using the Skywatcher system. Prz. Elektrotechniczny 2019, 95, 265–268. [Google Scholar] [CrossRef]
  43. Kruisselbrink, T.; Dangol, R.; van Loenen, E. Recommendations for long-term luminance distribution measurements: The spatial resolution. Build. Environ. 2020, 169, 106538. [Google Scholar] [CrossRef]
  44. Huijuan, T.; Zhen, H.; Tiantian, H.; Hui, Z. TM923 sctuma method for glare measurement based on a digital camera image in interior lighting. Laser Optoelectron. Prog. 2019, 56, 022201. [Google Scholar] [CrossRef]
  45. Vaaja, M.; Maksimainen, M.; Kurkela, M.; Virtanen, J.-P.; Rantanen, T.; Hyyppä, H. Approaches for Mapping Night-Time Road Environment Lighting Conditions. In Proceedings of the ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Nice, France (Virtual Event), 31 August–2 September 2020. [Google Scholar] [CrossRef]
  46. Spieringhs, R.M.; Smet, K.; Heynderickx, I.; Hanselaer, P. Road Marking Contrast Threshold Revisited. LEUKOS 2022, 18, 1–20. [Google Scholar] [CrossRef]
  47. Liu, C.-H.; Hsiao, C.-Y.; Gu, J.-C.; Liu, K.-Y.; Yan, S.-F.; Chiu, C.H.; Ho, M.C. HCL Control Strategy for an Adaptive Roadway Lighting Distribution. Appl. Sci. 2021, 11, 9960. [Google Scholar] [CrossRef]
  48. Zalesinska, M.; Wandachowicz, K. On the Quality of Street Lighting in Pedestrian Crossings. Energies 2021, 14, 7349. [Google Scholar] [CrossRef]
  49. Fryc, I.; Czyżewski, D.; Fan, J.; Gălăţanu, C. The Drive towards Optimization of Road Lighting Energy Consumption Based on Mesopic Vision—A Suburban Street Case Study. Energies 2021, 14, 1175. [Google Scholar] [CrossRef]
  50. Li, M.; Wu, P.; Ding, J.; Yao, Q.; Ju, J. The Circadian Effect Versus Mesopic Vision Effect in Road Lighting Applications. Appl. Sci. 2020, 10, 6975. [Google Scholar] [CrossRef]
  51. Price, R.B.; Labrie, D.; Sullivan, B.; Sliney, D.H. The potential ‘blue light hazard’from LED headlamps. J. Dent. 2022, 125, 104226. [Google Scholar] [CrossRef]
  52. Nie, J.; Chen, Z.; Jiao, F.; Chen, Y.; Zhan, J.; Chen, Y.; Pan, Z.; Kang, X.; Wang, Y.; Wang, Q.; et al. Utilization of far-red LED to minimize blue light hazard for dynamic semiconductor lighting. Leukos 2022, 19, 53–70. [Google Scholar] [CrossRef]
  53. Zhou, M.; Zhu, D.; Liao, X. Spectral design and optimization of white led light sources with low blue light hazard. Laser Optoelectron. Prog. 2019, 56, 182302. [Google Scholar] [CrossRef]
  54. Lee, S.; Matsumori, K.; Nishimura, K.; Nishimura, Y.; Ikeda, Y.; Eto, T.; Higuchi, S. Melatonin suppression and sleepiness in children exposed to blue-enriched white LED lighting at night. Physiol. Rep. 2018, 6, e13942. [Google Scholar] [CrossRef] [Green Version]
  55. Kobav, M.B.; Bizjak, G. LED spectra and melatonin suppression action function. Light Eng. 2012. [Google Scholar]
  56. Jakubowski, P. Artificial light sources as light pollutant of humans melatonin suppression. Photon-Lett. Pol. 2019, 11, 78–80. [Google Scholar] [CrossRef]
  57. Nie, J.; Zhou, T.; Chen, Z.; Dang, W.; Jiao, F.; Zhan, J.; Chen, Y.; Chen, Y.; Pan, Z.; Kang, X.; et al. Investigation on entraining and enhancing human circadian rhythm in closed environments using daylight-like LED mixed lighting. Sci. Total. Environ. 2020, 732, 139334. [Google Scholar] [CrossRef]
  58. Cajochen, C.; Kräuchi, K.; Wirz-Justice, A. Role of Melatonin in the Regulation of Human Circadian Rhythms and Sleep. J. Neuroendocr. 2003, 15, 432–437. [Google Scholar] [CrossRef] [Green Version]
  59. Hayes, K.R.; E Baggs, J.; HogenEsch, J.B. Circadian clocks are seeing the systems biology light. Genome Biol. 2005, 6, 219. [Google Scholar] [CrossRef] [Green Version]
  60. Jakubowski, P.; Fryc, I. Metrological requirements for measurements of circadian radiation. Opt. Appl. 2018, 48, 697–704. [Google Scholar] [CrossRef]
  61. Zheng, L.; Guo, Z.; Yan, W.; Lin, Y.; Lu, Y.; Kuo, H.-C.; Chen, Z.; Zhu, L.; Wu, T.; Gao, Y. Research on a Camera-Based Microscopic Imaging System to Inspect the Surface Luminance of the Micro-LED Array. IEEE Access 2018, 6, 51329–51336. [Google Scholar] [CrossRef]
  62. Czyżewski, D. Selected problems of defining the luminous area of electroluminescent diodes. Prz. Elektrotechniczny 2008, 84, 125–128. [Google Scholar]
  63. Jongewaard, M. Guide to selecting the appropriate type of light source model. In Modeling and Characterization of Light Sources; SPIE: Bellingham, WA, USA, 2002; pp. 86–98. [Google Scholar]
  64. Słomiński, S. Luminance mapping to the light source model—Possibilities to use a MML in the lighting technology field. Prz. Elektrotech. 2011, 4, 87–89. [Google Scholar]
  65. Czyżewski, D. Research on Luminance Distributions of Chip-On-Board Light-Emitting Diodes. Crystals 2019, 9, 645. [Google Scholar] [CrossRef] [Green Version]
  66. Goldstein, P. Efficient calculation of luminance variation of a luminaire that uses LED light sources. In Seventh International Conference on Solid State Lighting; SPIE: Bellingham, WA, USA, 2007; Volume 6669, pp. 33–42. [Google Scholar]
  67. Novak, T.; Socha, B.; Carbol, Z.; Sokansky, K. Luminance evaluation of LED indoor luminaires for workspaces lighting. In Proceedings of the 13th International Scientific Conference Electric Power Engineering, Brno, Czech Republic, 2012; pp. 1185–1188. [Google Scholar]
  68. CEN/TC EN 13201-4:2015; Road Lighting—Part 4: Methods of Measuring Lighting Performance. iTeh Standards: Etobicoke, ON, Canada, 2015.
  69. Żagan, W. Oprawy Oświetleniowe—Kształtowanie Rozsyłu Strumienia Świetlnego i Rozkładu Luminancji (Eng. Luminaires—The Modelling of Luminous Flux and Luminance Distribution); OWPW: Warsaw, Poland, 2012; ISBN 978-83-7814-054-2. [Google Scholar]
  70. Holmes, J. A reference distance for the photometry of projectors. Light. Res. Technol. 1981, 13, 96–98. [Google Scholar] [CrossRef]
  71. CEN/TC EN 231:2019; CIE Classification System of Illuminance and Luminance Meters. iTeh Standards: Etobicoke, ON, Canada, 2019.
  72. Skarżyński, K.; Żagan, W.; Krajewski, K. LED Luminaires: Many Chips—Many Photometric and Lighting Simulation Issues to Solve. Energies 2021, 14, 4646. [Google Scholar] [CrossRef]
  73. Oleszyński, T. Miernictwo Techniki Świetlnej (Eng. Metrology of Lighting Technology); PWN: Warsaw, Poland, 1957. [Google Scholar]
  74. Tyukhova, Y.; Waters, C. An Assessment of High Dynamic Range Luminance Measurements with LED Lighting. Leukos 2014, 10, 87–99. [Google Scholar] [CrossRef] [Green Version]
  75. Buyukkınacı, B.; Onaygil, S.; Guler, O.; Yurtseven, M.B. Comparison of road lighting calculations with measurements using conventional and camera luminance meters. Light Eng. 2016, 24, 56–63. [Google Scholar]
  76. Czyzewski, D. Monitoring of the lighting conditions of a street illuminated with road lights equipped with LEDs. Prz. Elektrotech. 2010, 86, 170–172. [Google Scholar]
  77. Rusu, A.V.; Galatanu, C.D.; Livint, G.; Lucache, D.D. Measuring Average Luminance for Road Lighting from Outside the Carriageway with Imaging Sensor. Sustainability 2021, 13, 9029. [Google Scholar] [CrossRef]
  78. Czyżewski, D. The LEDs luminance distribution measurement quality dependency on image focusing. Photon-Lett. Pol. 2020, 12, 121–123. [Google Scholar] [CrossRef]
  79. Słomiński, S. Identifying problems with luminaire luminance measurements for discomfort glare analysis. Light. Res. Technol. 2016, 48, 573–588. [Google Scholar] [CrossRef]
  80. Jakubiec, J.A.; Inanici, M.N.; Van Den Wymelenberg, K.; Mahic, A. Improving the Accuracy of Measurements in Daylit Interior Scenes Using High Dynamic Range Photography. In Proceedings of the 32nd PLEA Conference, Los Angeles, CA, USA, 11 July 2016. [Google Scholar]
  81. CEN/TC EN 13201-2:2015; Road Lighting—Part 2: Performance Requirements. iTeh Standards: Etobicoke, ON, Canada, 2015.
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Figure 1. The set-up for indirect luminance measurement.
Figure 1. The set-up for indirect luminance measurement.
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Figure 2. (a) The view from the meter’s lens, showing the measuring field exceeding the size of the measured light source. The incorrect direct measurement of luminance is shown—the area of the illuminating LED covers approximately 25% of the measuring field. (b) The correct direct measurement of luminance—the area of the luminous LED covers 100% of the measurement field.
Figure 2. (a) The view from the meter’s lens, showing the measuring field exceeding the size of the measured light source. The incorrect direct measurement of luminance is shown—the area of the illuminating LED covers approximately 25% of the measuring field. (b) The correct direct measurement of luminance—the area of the luminous LED covers 100% of the measurement field.
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Figure 3. Measurement of road lighting, where in figure (a) the luminance range was selected manually and in figure (b), where the ILMD software matched the meter range to the maximum luminance level of the luminaires.
Figure 3. Measurement of road lighting, where in figure (a) the luminance range was selected manually and in figure (b), where the ILMD software matched the meter range to the maximum luminance level of the luminaires.
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Figure 4. The set-up for precise luminance measurements (measurements up to 1 m), where: 1—goniophotometer, 2—cooling system, 3—tested high-power LEDs, 4—laser, 5—micrometre screw, 6—measuring table, 7—luminance meter, 8—DC power supply, 9—laboratory multimeter, 10—temperature meter, 11—lens.
Figure 4. The set-up for precise luminance measurements (measurements up to 1 m), where: 1—goniophotometer, 2—cooling system, 3—tested high-power LEDs, 4—laser, 5—micrometre screw, 6—measuring table, 7—luminance meter, 8—DC power supply, 9—laboratory multimeter, 10—temperature meter, 11—lens.
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Figure 5. The measuring set-up for luminance measurements above 1 m.
Figure 5. The measuring set-up for luminance measurements above 1 m.
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Figure 6. LED1, LED2, and LED3, with the eight measurement areas plotted, on the luminance distributions from the direction of the optical axis (C0γ0).
Figure 6. LED1, LED2, and LED3, with the eight measurement areas plotted, on the luminance distributions from the direction of the optical axis (C0γ0).
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Figure 7. The view of the luminance distribution on the surface of LED 2 for different measurement distances (the left picture shows the view of the actual LED image on the ILMD, and the right picture shows a magnification of the image of the tested LED2).
Figure 7. The view of the luminance distribution on the surface of LED 2 for different measurement distances (the left picture shows the view of the actual LED image on the ILMD, and the right picture shows a magnification of the image of the tested LED2).
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Figure 8. The relative maximum luminance (related to Lmax for 180 mm) for LED1. LED2 and LED3 as the function of pixel number.
Figure 8. The relative maximum luminance (related to Lmax for 180 mm) for LED1. LED2 and LED3 as the function of pixel number.
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Figure 9. The relative average luminance (related to Lavr for 180 mm) for LED1, LED2 and LED3 as a function of the number of pixels on the ILMD array.
Figure 9. The relative average luminance (related to Lavr for 180 mm) for LED1, LED2 and LED3 as a function of the number of pixels on the ILMD array.
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Figure 10. The comparison of energy consumption for an installation lighting a 10-km road. Different photometric distances of individual LEDs installed in the luminaire were used for the comparison.
Figure 10. The comparison of energy consumption for an installation lighting a 10-km road. Different photometric distances of individual LEDs installed in the luminaire were used for the comparison.
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Table
Table 1. Technical parameters of the LMK98-3 Color luminance meter.
Table 1. Technical parameters of the LMK98-3 Color luminance meter.
ParameterLMK98-3 Color
SensorCCD Sony ICX 285 AL
resolution (effective pixels)1380 (H) × 1030 (V)
pixel ratio6.45 μm × 6.45 μm
sensor area8.9 (H) × 6.64 (V) mm2 (2/3″)
video signal12 bit digital
measuring range>300 Mcd/m2 with neutral density filters
measurement accuracy3% (L standard illuminant A)
Table
Table 2. The summary of technical parameters selected for presentation of high-power LEDs.
Table 2. The summary of technical parameters selected for presentation of high-power LEDs.
ParameterLED1LED2LED3
appearance 1Energies 16 01199 i001Energies 16 01199 i002Energies 16 01199 i003
maximum dimension3.45 mm2.7 mm4.5 mm
nominal luminous flux (85 °C)156 lm365 lm693 lm
colour rendering index (CRI)707070
typical forward current0.350 A0.700 A0.640 A
wattage0.945 W 1.96 W3.84 W
maximum junction temperature150 °C135 °C125 °C
thermal resistance3.0 °C/W 2.4 °C/W1.8 K/W
1 The pictures of high-power LEDs are taken from the data sheets of light source manufacturers.
Table
Table 3. Mean luminance, maximum luminance, and minimum luminance for different areas of examined LED surfaces (LED1, LED2 and LED3).
Table 3. Mean luminance, maximum luminance, and minimum luminance for different areas of examined LED surfaces (LED1, LED2 and LED3).
The Analysed Area on the LED SurfaceLuminance [Mcd/m2] on Power LED Surface for Each C0γ0 Direction
LED1 LED2 LED3
LmaxLavrLminLmaxLavrLminLmax LavrLmin
Area no 120.2512.781.4333.0018.440.4916.8210.501.44
Area no 220.2514.976.1733.0022.591.0916.8211.475.31
Area no 320.2516.519.0433.0025.873.5116.8212.376.63
Area no 420.2517.9511.7633.0027.5320.7316.8211.927.04
Area no 520.2518.6013.2032.4528.0820.7315.4510.407.04
Area no 620.2518.8015.0832.4528.1622.6013.909.467.04
Area no 720.1119.0417.0531.4128.4924.069.418.588.15
Area no 820.1119.2917.9630.8628.4424.158.868.508.15
Table
Table 4. The summary of test results and calculations, the effect of varying the photometric distance on the maximum and mean luminance results for LED2.
Table 4. The summary of test results and calculations, the effect of varying the photometric distance on the maximum and mean luminance results for LED2.
Photometric Distance
[mm]		Summary of LED2 Research ResultsSummary of LED2 Calculation Results
LmaxLavrNumber of Pixels (Px)Lmax(x)/Lmax(180) · 100Lavr(x)/Lavr(180) · 100Px/Px(max) ·
1000
[Mcd/m2][Mcd/m2][-][%][%][‰]
18033.017.851,73010010036.11
28032.417.711,79098.299.68.23
30632.317.5892597.998.56.23
37031.217.5509794.598.33.56
48630.416.4270192.192.21.89
65539.415.6129389.187.70.90
81829.214.9116988.583.80.82
94029.113.764188.277.30.45
135428.412.133386.168.30.23
377822.510.23375.257.50.023
80499.742.741731.215.40.012
11,4653.190.91914.85.10.0063
Table
Table 5. Technical data for a luminaire fitted with high-power LEDs.
Table 5. Technical data for a luminaire fitted with high-power LEDs.
Technical ParameterLuminaire for M2 Class
luminaire photometric intensity curves (LPIC)Energies 16 01199 i004
light source typeLED
number of LEDs160
luminaire luminous flux28,900 [lm]
luminaire power196 [W]
CCT4000 K
Ra70 [-]
Table
Table 6. Luminaire placement ranges.
Table 6. Luminaire placement ranges.
Technical ParameterLuminaire for M2 Class
spacing (S) (module) [m]35–60
luminaire height (H) [m]10–14
inclination angle (Q) [°] 0–15
overhang (OH) [m]0–2
Table
Table 7. The analysis of the effect of the photometric distance of single LEDs on the results of lighting installation projects.
Table 7. The analysis of the effect of the photometric distance of single LEDs on the results of lighting installation projects.
Photometric Distance of the LEDs Used in the LuminaireArrangement of Luminaires
S/H/Q/OH
[m/m/°/m]		Indicator
Dp
[mW/(lx m2)]		Indicator
De
[kWh/m2/year]		Power/10 km
[kW/10 km]		Energy/10 km
[MWh/10 km/year]
280 mm
(reference)		57/14/5/2131.2269.0289.77
306 mm56/14/0/2131.2470.2294.71
486 mm54/13.5/5/2141.2972.9306.23
1354 mm41/12/5/2181.795.6401.72
3778 mm36/10/10/2201.94109.0457.70
8049 mm14/9/10/2504.98278.31177.18
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Czyżewski, D. The Photometric Test Distance in Luminance Measurement of Light-Emitting Diodes in Road Lighting. Energies 2023, 16, 1199. https://doi.org/10.3390/en16031199

AMA Style

Czyżewski D. The Photometric Test Distance in Luminance Measurement of Light-Emitting Diodes in Road Lighting. Energies. 2023; 16(3):1199. https://doi.org/10.3390/en16031199

Chicago/Turabian Style

Czyżewski, Dariusz. 2023. "The Photometric Test Distance in Luminance Measurement of Light-Emitting Diodes in Road Lighting" Energies 16, no. 3: 1199. https://doi.org/10.3390/en16031199

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