Irena Fryc

Museums face a conflict between energy-efficient gallery lighting and protecting light-sensitive collections from photochemical damage: increasing the luminous efficacy of white LEDs requires shifting spectral power toward the high-energy blue band, accelerating degradation of organic materials. Prior work treated these separately; this study links them via a shared spectral property, the blue-to-yellow emission balance. For four artifact classes (water colors on paper rag, oil colors on canvas, textile materials, and rag paper), luminous efficacy is calculated from spectral radiant power distributions, alongside a material-specific damage factor per unit of useful light derived from first-order kinetics. For each class and color temperature (CCT), this factor is benchmarked against a reference halogen source, yielding a relative photochemical damage index—a relative comparison rather than a computed permissible dose or exposure time—that flags spectra with lower hazard than current practice. Across the database, the blue-to-yellow spectral balance shifts faster than efficacy gains above 4000–5000 K, so higher CCTs carry a growing conservation cost; class-specific limits cut radiant power input in robust material galleries without compromising sensitive ones. Evaluated on nearly 2850 commercial LED spectra, the index gives lighting engineers and conservators a quantitative tool for selecting energy-efficient, conservation-safe LED products.

This paper presents comprehensive practical solutions for reducing light pollution in urban LED lighting systems through two complementary approaches: (1) spectral conversion filters for retrofitting existing 4000 K nominal CCT LED luminaires, and (2) systematic methodology for designing environmentally conscious lighting installations. The conversion filter method achieves nominal CCT reduction from 4000 K to CCT ≤ 2700 K, providing a cost effective alternative to complete infrastructure replacement. Full Text: PDF References I. Fryc, S. Bará, M. Aubé, J.C. Barentine, J. Zamorano, "On the Relation between the Astronomical and Visual Photometric Systems in Specifying the Brightness of the Night Sky for Mesopically Adapted Observers", LEUKOS 18, 447 (2022). CrossRef S. Bará, F. Falchi, Artificial light at night: a global disruptor of the night-time environment, Phil. Trans. R. Soc. B 378, 20220352 (2023). CrossRef I. Fryc, The night sky light pollution created by outdoor luminaires, Przegląd Elektrotechniczny 1, 48 (2017). CrossRef J. Falcón, A. Torriglia, D. Attia, F. Viénot, C. Gronfier, F. Behar-Cohen, C. Martinsons, D. Hicks, Exposure to Artificial Light at Night and the Consequences for Flora, Fauna, and Ecosystems, Front. Neurosci. 14, 602796 (2020). CrossRef R. Supronowicz, I. Fryc, Urban park lighting as a source of botanical light pollution, Photon.Lett.PL 11, 90 (2019). CrossRef K.J. Gaston, J. Bennie, T.W. Davies, J. Hopkins, The ecological impacts of nighttime light pollution: a mechanistic appraisal, Biological Reviews 88, 912 (2013). CrossRef T. Longcore, C. Rich, Ecological light pollution, Frontiers in Ecology and the Environment 2, 191 (2004). CrossRef Arrêté du 27 décembre 2018 relatif à la prévention, à la réduction et à la limitation des nuisances lumineuses, (2018). DirectLink Ministère de la Transition Écologique et Solidaire: Bilan de l'application de l'arrêté du 27 décembre 2018 relatif à la prévention, à la réduction et à la limitation des nuisances lumineuses. Paris 2021, (n.d.). DirectLink Generalitat de Catalunya. Decret 190/2015, de 25 d'agost, de desplegament de la Llei 6/2001, de 31 de maig, d'ordenació ambiental de l'enllumenament per a la protecció del medi nocturn. Diari Oficial de la Generalitat de Catalunya, 2015. DirectLink Jefatura del Estado, Ley 31/1988, de 31 de octubre, sobre Protección de la Calidad Astronómica de los Observatorios del Instituto de Astrofísica de Canarias, 1988. DirectLink Joint Research Centre: Revision of the EU Green Public Procurement Criteria for Road Lighting and Traffic Signals. Technical Report, European Commission, 2019. DirctLink CIE TC 5-28, CIE 150:2017 Guide on the Limitation of the Effects of Obtrusive Light from Outdoor Lighting Installations, 2nd Edition, CrossRef CIE TC 4-56, CIE 234:2019 A Guide to Urban Lighting Masterplanning, CrossRef International Dark Sky Community Program Guidelines, (2018). DirectLink A. Machnowska, S. Kołomański, A. Kotarba, T. Ściężor, Zanieczyszczenie światłem w Polsce. Raport 2023, (2023). DirectLink S. Jost, A. Thorseth, T. Poikonen, P. Blattner, T. Gerloff, A. Kokka, P. Dekker, M. Smid, A. Ferrero, T. Kubarsepp, P. Gal, S. Källberg, A. Klej, G. Brida, T. Reiners, K. Ludwig, M. Schneider, L. Hui, EMPIR 15SIB07 PhotoLED - Database of LED product spectra, (2021) CrossRef ANSI C78.377 American National Standard for Electric Lamps-Specifications for the Chromaticity of Solid State Lighting (SSL) Products, (2024). DirectLink A. Hänel, T. Posch, S.J. Ribas, M. Aubé, D. Duriscoe, A. Jechow, Z. Kollath, D.E. Lolkema, C. Moore, N. Schmidt, H. Spoelstra, G. Wuchterl, C.C.M. Kyba, Measuring night sky brightness: methods and challenges, Journal of Quantitative Spectroscopy and Radiative Transfer 205, 278 (2018). CrossRef T. Esposito, K. Houser, Correlated color temperature is not a suitable proxy for the biological potency of light, Sci Rep 12, 20223 (2022). CrossRef M. Pagliaro, Safe and Truly Ecofriendly LED Lighting, Energy Science & Engineering (2025) ese3.70272. CrossRef EN 13201:2015: Road lighting - Part 2: Performance requirements. European Committee for Standardization, Brussels 2015, DirectLink

Energy efficiency in road lighting is increasingly critical for sustainable urban development, yet numerical indicators essential for objective evaluation are often misunderstood or misapplied. This paper addresses fundamental misconceptions in interpreting the Power Density Indicator (PDI), a key metric for assessing lighting system efficiency. Through analysis of Romanian street lighting modernization projects and extensive literature review, we demonstrate widespread misunderstanding of PDI’s properties, including inappropriate summation across streets and failure to recognize its independence from road class. We present a comprehensive methodology for PDI interpretation and optimization through spatial visualization of Luminous Intensity Distribution Curves (LIDCs) using MATLAB’s MESH function. The theoretical framework derives minimum achievable PDI values as a function of LED-specific efficacy and system utilance. Case studies from 181 streets in Romanian cities reveal significant optimization potential. Finally, we demonstrate, through computational simulation, the theoretical ideal: a perfectly adapted LIDC achieving unitary utilance, confirming that minimum PDI depends solely on LED efficacy and optical efficiency. These findings provide practical guidance for designers to optimize energy efficiency while meeting photometric requirements.

Energy efficiency in road lighting is increasingly critical for sustainable urban devel-opment, yet numerical indicators essential for objective evaluation are often misun-derstood or misapplied. This paper addresses fundamental misconceptions in inter-preting the Power Density Indicator (PDI), a key metric for assessing lighting system efficiency. Through analysis of Romanian street lighting modernization projects and extensive literature review, we demonstrate widespread misunderstanding of PDI's properties, including inappropriate summation across streets and failure to recognize its independence from road class. We present a comprehensive methodology for PDI interpretation and optimization through spatial visualization of luminous intensity distribution curves (LIDC) using MATLAB's MESH function. The theoretical frame-work derives minimum achievable PDI values as a function of LED specific efficacy and system utilance. Case studies from 181 streets in Romanian cities reveal significant optimization potential. Finally, we demonstrate through computational simulation the theoretical ideal: a perfectly adapted LIDC achieving unitary utilance, confirming that minimum PDI depends solely on LED efficacy and optical efficiency. These findings provide practical guidance for designers to optimize energy efficiency while meeting photometric requirements.

This study presents the first comprehensive investigation establishing the relationship between color consistency and luminous efficacy of radiation (LER) in phosphor-converted light-emitting diodes (LEDs), introducing novel selection criteria for energy-efficient applications. A systematic analysis of LED sources with nominal correlated color temperature (CCT) values of 3000 K and 4000 K across color-rendering index (CRI Ra) thresholds (≥60 and ≥80) was conducted, evaluating spectral power distributions (SPD) and chromaticities relative to 3-step, 5-step color-consistency circles, and 7-step American National Standards Institute (ANSI) quadrangles. Novel findings reveal a previously uncharacterized strong positive correlation between color consistency and luminous efficacy across all analyzed LED sources. LEDs with chromaticities within 3-step color-consistency circles consistently demonstrated superior LER values compared to 5-step boundaries, while sources outside established circles showed significantly inferior energy performance despite meeting nominal CCT requirements. The research establishes that tighter color-consistency tolerances directly correlate with enhanced luminous efficacy, revealing an intrinsic relationship between color quality and energy performance. These breakthrough findings introduce a paradigm shift in LED selection methodology, providing lighting professionals with evidence-based criteria that simultaneously optimize color consistency and energy efficiency, enabling more sustainable lighting solutions through integrated quality–performance assessment.

Selecting LED retrofits for examination rooms in healthcare buildings involves setting the right balance between lighting quality and energy efficiency. In the case of LEDs incorporated in luminaires used in medical examination rooms, it is essential to consider not only the correlated color temperature (CCT) and color rendering index (CRI Ra) in compliance with the lighting standards, but also the cyanosis observation index (COI) that meets the more demanding regulations of certain countries. In this work, the Color Preference Criteria (CPC) method is used to select LED retrofits for this application. The LEDs classified as P1 according to the CPC method were found to meet the required COI level.

This study carried out a literature search and selection in accordance with the PRISMA 2020 protocol to conduct a complete review of the literature describing the electrical, photometrical, and colorimetric parameters of LEDs. Based on it, a significant research gap was found in the field of LED-based lighting retrofits. We prove that there is a lack of publications indicating the relationship between the energy consumption of LED retrofits and user preferences concerning the quality of lighting. This article presents an effective new method for selecting LEDs to retrofit typical 3000, 4000, and 6500 K fluorescent lighting installations in buildings. It is shown that when selecting an LED replacement for a fluorescent source, consideration of the classically used parameters in the field of lighting technology to describe the quality of white light, specifically correlated color temperature and the color rendering index, is insufficient. We demonstrate that energy efficiency and the color preference criteria for retrofitted LEDs must be considered and balanced with the potential impact on circadian rhythms as assessed by the melanopic daylight efficacy ratio. This research proves that LED replacements with the best color preference properties (P1 class in the CPC classification of ANSI/IES TM30-20 method) correspond to the least energy-efficient light sources.

A variety of LED types can be employed for street and road lighting purposes. White phosphor-converted LEDs represent the most widely used option. However, amber LEDs are increasingly being used to reduce some negative effects associated with light pollution. These LEDs can be manufactured using both phosphor-converted and monochromatic direct chip technologies. This paper addresses the link between the reduction in short-wavelength light emissions which contribute to sky glow and the energy efficiency of LED-based road lighting. This paper focuses on an example illustrating the common misconception that reducing light pollution also means saving energy. Through the consideration of how spectral power distribution influences both mesopic vision and the amount of emitted blue light, it has been concluded that while monochromatic direct amber LEDs consume more energy than their white or amber phosphor-converted counterparts, their use in outdoor lighting is justifiable due to their potential effects of reducing sky brightness.