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

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.

The Influence of a Photometric Distance on Luminance Measurements

“…The measurements were intended to demonstrate the constancy or variability of the results obtained for different measurement distances. The analysis of the obtained results would allow the measurements to be compared with those obtained in other studies that concerned high-luminance LEDs [63].…”

“…For example, using the ILMD laboratory meter when measuring high-luminance LEDs, the reference image for LED1 occupied 56,640 px, and for LED3 it occupied 149,600 px. In relation to these reference images, the measured images covering about 6000 px for LED1 and about 50,000 px for LED3 ensure the measurement accuracy of 99% [63]. It all depends on the output size of the image and the uniformity of the luminance distribution on a given image.…”

“…This surface had a very uniform luminance distribution. Hence, it seems interesting to compare the obtained measurement results with those presented in the literature for measurements of high-illuminance LEDs with an uneven luminance distribution on their luminous surface [63].…”

“…Figure 1 shows the results of measurements of the luminance distribution on the LED surface, where Figure 1a shows the measurement from the distance of 180 mm (large LED image), and Figure 1b One research paper addresses the issue of the influence of selection of luminance photometric distance on the measurement results [63]. Based on the research, recommendations were given on how to perform LED measurements to maintain a high accuracy of the results One research paper addresses the issue of the influence of selection of luminance photometric distance on the measurement results [63]. Based on the research, recommendations were given on how to perform LED measurements to maintain a high accuracy of the results for different measurement methods.…”

Study of LED Retrofit Lamps in HSPV Luminaires Based on Photometric Method for Road Lighting

“…Studies on the photometric impact of replacing the original light source are limited (Abdullah et al, 2021). Recent studies regarding LED measurement have shown that LED has different characteristics than conventional luminaires and may require different measurement approaches for correct evaluation (Czyżewski, 2023).…”