New Perspectives on Lighting

Lighting has experienced dramatic developments in the last two decades. The simplest example to understand this is the fact that just twenty years ago, we suspected that humans had one more photoreceptor in addition to the apparently well-known rods and cones but did not know what it was. Since ipRGCs were identified as the photoreceptors initiating at least one non-visual path, the lighting research community has been undergoing a revolution, and its consequences for safety, ergonomics, medicine, psychology, productivity, and many other fields will not be fully understood in the short term. Lighting nowadays involves technological development, design optimization [1], and, of course, the adoption of sustainable principles [2,3,4]. As the lighting technology is now enhanced, it is possible to increase energy savings further through lighting controls [5,6,7,8,9], including additional parameters such as the factor of the users’ expectations and needs [10,11], biophilic design [12], harvesting of daylight [13,14], wellbeing, productivity, and providing proper lighting when and where it is needed [15,16,17,18,19]. If other revolutionary milestones, such as the massive introduction of LEDs in fields such as automotive lighting, indoor and outdoor lighting, or the progressive introduction of infrared lighting, are considered complementary to the new perspectives brought by the discovery of ipRGCs, lighting can be considered one of the most exciting and challenging branches of technical knowledge. The present Editorial focuses on these new perspectives and the unexpected applications that could appear in the future.

1. The Editorial “New Perspectives on Lighting”

The mentioned revolution experienced by lighting permeates all its fields and applications. “New Perspectives on Lighting” has covered a wide spectrum of areas and perfectly shows the new conception of lighting and the consequent advances. In this brief Editorial, the main highlights in each area will be summarized.

1.1. Urban Lighting

Using the results of Zielinska-Dabkowska’s work, the overlooked issue of urban illumination and its impact should be addressed in SDG11: Sustainable Cities and Communities. It is crucial to inform politicians and city authorities committed to SDG11 about this gap and to urge them to take appropriate actions to minimize light pollution and its negative effects. Responsible urban illumination, necessary for cities to be sustainable, healthier, and environmentally responsible after dark, can be achieved by incorporating the following actions into planning documents: (A) Fair Access to Darkness and Quality Lighting: Every city resident deserves fair access to both darkness and quality lighting without discrimination. The design process for responsible urban illumination should prioritize darkness, ensuring that added light does not obstruct views of the stars or disregard the importance of nocturnal placemaking and safety. (B) Optimizing Social Benefits and Limiting Costs: Urban illumination projects should optimize the social benefits of outdoor lighting at night while minimizing environmental and financial costs. (C) Early Collaboration with Lighting Professionals: Engage lighting professionals (urban lighting designers, architectural lighting designers, and illuminating engineers) early in the design process for urban, building, and landscape projects. (D) Interdisciplinary Collaboration: Collaborate with researchers and experts from various disciplines (e.g., astronomers, ecologists, and biologists) to access evidence-based information on contemporary issues related to sustainable cities. (E) Educating Clients: Educate public and private clients on the importance of responsible urban lighting to make informed decisions for the environment and the health and well-being of residents. Encourage active participation in applying existing regulatory frameworks and establishing local regulations where they are absent or lacking. (F) Community Involvement: The local community should be an active participant in urban lighting projects, allowing citizens to voice concerns, propose ideas, and influence decisions. (G) Applying the Five Principles of Responsible Outdoor Lighting: Ensure that all light has a clear purpose, is directed only where needed, is no brighter than necessary, is dimmed or turned off when not required, and uses warmer-colored lights where possible. (H) Performing Environmental and Health Lighting Impact Assessments: Conduct Environmental Lighting Impact Assessments (ELIA) and Health Lighting Impact Assessments (HLIA) for all urban illumination projects, including temporary events, to evaluate potential adverse effects on wildlife and humans. (I) Embracing Lighting Technology: Seek support and direction from the lighting industry to sustain nighttime biodiversity and reduce energy consumption through advanced lighting technology. (J) Promoting a Circular Economy: Incorporate circular economy principles in the project brief, design, specification, manufacturing, and installation processes to reduce the use of natural resources, electronic waste, and energy and to lower the carbon footprint. (K) Post-Completion Verification: After project completion, conduct night visits with all community stakeholders to ensure that the urban lighting design meets the agreed principles and has been fully implemented.

1.2. Indoor Lighting

Interior spaces with mirrored walls present unique and paradoxical challenges to visual perception. Unlike traditional walls, mirrored walls extend the visual field, effectively doubling perceived lengths, although the electrical installation stops just before the mirror. Additionally, reflections of objects behind the user increase the visual load and introduce spatial inversions (left to right and vice versa). The proposed model of the Peña–Garcia research, which assumes the existence of twin virtual spaces, goes beyond a simple estimation of luminaire quantities or photometric parameters. It provides a comprehensive perspective on visual tasks by incorporating both the real room and its virtual counterpart reflected in the mirror. These virtual spaces contain planes and objects where visual tasks occur. The geometric data from this theoretical model is then used as input in standard calculation tools. Specifically, Pena–Garcia’s model symmetry consideration can be applied in two ways, i.e., quick pre-dimensioning with the lumen method, which does not account for average uniformity and glare, and detailed computational calculations using programs like DIALux [20]. These programs provide metrics such as average illuminance, average uniformity, and glare. For computational calculations, it is sufficient to consider the virtual spaces behind the mirrors, while for the actual installation, only the luminaire quantities and their distribution in the real space are considered. This makes the proposed method versatile and applicable in any situation involving mirrored walls. In spite of the assumption of perfect reflectance of the mirrors, they generally reflect almost all the luminous flux and create a nearly perfect and symmetric image of each luminary, which the model treats as real in its initial steps.

1.3. LED Retrofit

Roy and Krames examined the active power control of retrofit LED lamps and, more specifically, LED tubes, the most common retrofit in office buildings. In summary, the authors investigated real-world conditions for the LED retrofit replacement of linear fluorescent lamps by testing electronic ballasts, a total of 129 different types, recovered from luminaires across various countries in Europe with state-of-the-art commercially available LED tube products. The findings revealed that the lamp power varied significantly depending on the specific lamp/ballast combination. The lamp’s power draw ranged from as low as half to as high as twice the lamp’s rated or declared value. In low-power scenarios, the installed lamp fails to meet the intended lighting design metrics. In high-power scenarios, the lamp does not provide the anticipated energy savings or greenhouse gas emissions reductions, raising concerns about safety and lamp longevity. For this reason, the authors introduced the design of an active-power–control driver for tube LED retrofit. The retrofit with the new driver met the EU’s Ecodesign guideline in 82% of the examined cases. The results show that, with proper design, retrofit LED tube lamps can deliver predictable power draw and reliable energy savings across all available sockets, regardless of the legacy ballasts installed in different luminaires over the years.

1.4. Glare

Viktorova et al., estimated the glare encountered from the perspective of Czech passenger-car drivers. The authors’ findings indicate that about one-quarter of drivers on Czech roads encounter glare daily, while 30% experience it once a week, regardless of the street type. These figures were comparable to those in the UK [21,22], where the glare was not clear whether it was from high beams or low beams. In this study, only 6.9% of participants expressed this uncertainty. The perception that low beams are as much a source of glare as high beams is potentially concerning. One of the main findings of the paper highlights a strange behavior among drivers. More than 60% of respondents preferred the road view provided by HIDs and LEDs, which have a spectrum from 4000 K to 6000 K, although they frequently complained about glare from mostly 4000 K (neural white) or cooler (more than 4000 K) light sources. This preference aligns with the results of previous research [23,24,25,26,27,28].

1.5. Power Quality of LED

Electric stress from both voltage and current poses a serious threat to LED luminaires, driven by the growing complexity of power electronic circuits and aggressive IC technology scaling. Letha et al. [25] examined catastrophic failures in LED lamps caused by voltage stress, focusing on both heatsink and filament-type lamps. Six groups of 180 LED lamps each were exposed to various voltage profiles, including a control group, short interruptions, transients, overvoltage, undervoltage, and harmonics. A detailed failure analysis was then conducted on filament lamps. The general findings of the research can be summarized as follows: (A) None of the lamps failed due to undervoltage, harmonics, transients, or short interruptions, indicating no need for accelerated aging tests for these phenomena. (B) All failures occurred in filament-type lamps under overvoltage test conditions. (C) In an accelerated overvoltage test, lamps were exposed to 120% voltage for 100 h, and none failed. Higher voltage exposure would likely lead to other failure mechanisms, making comparisons difficult. This research provided insights into the accelerated test procedures necessary for evaluating LED lamps under different voltage profiles. It concluded that overvoltage stress is critical for filament-type lamps, while other voltage profiles (undervoltage, harmonics, transients, and short interruptions) do not affect LED aging. These findings can guide LED manufacturers and standardization committees in setting accelerated aging test profiles.

1.6. Daylighting

Castillo-Martínez and Peña-García examined the visual performance of pedestrians, considering the impact of urban groves. They focused on species in the Mediterranean region. This study highlights the importance of considering various environmental and technological factors in urban planning and design to enhance the visual performance and well-being of pedestrians. The results underscore the significant interplay between daylight, visual perception, urban groves, and well-being. This synergy, although intuitively accepted, has profound implications that must be carefully considered when planning new urban spaces or reforming existing ones. There were three key considerations as follows: (A) Tree-Species Selection: In urban spaces such as squares, tree species should be chosen based on multiple factors. Traditionally, these factors include aesthetics, shade provision, water requirements, and potential interactions with buildings and other urban features. However, the visual performance and accurate values of average illuminance and uniformity on urban roads and street pavements are strongly influenced by the presence of groves during the daytime. Therefore, these factors must be considered when selecting tree species. (B) Photometric Variability: Photometric parameters, particularly illuminance on pavements, walls, and pedestrians’ eyes, vary greatly during the day due to the sun’s apparent path across the sky (ecliptic). Seasonal variations in solar altitude and changing weather conditions (clouds, aerosol levels, etc.) also affect the visual conditions for pedestrians. This variability means that a tree species suitable for a traffic area may differ from one that is ideal for a pedestrian space. Climate conditions and air quality are also crucial factors in achieving a rational design that balances aesthetics, perceived security, ecological value, and solar protection. (C) Shading and Uniformity: Despite the aforementioned variability, an appropriate grove can ensure high average uniformities in shaded zones.

1.7. Light Quality

Bustamante et al. focused on the effectiveness of different metrics in terms of color discrimination, considering related parameters such as color temperature and gamut saturation. The conclusions of the research drawn are based on specific conditions, such as two-color scenarios and a range of color caps for the FM-100 trial, involving 115 respondents and analyzing 805 surveys. The main research findings were as follows: (A) As anticipated, daylight offers the maximum color rendering, followed by neutral white with a correlated color temperature (CCT) of 4000 K, cool white (6500 K), and warm white (2700 K) LEDs. These were followed by cool white (6500 K) from fluorescent sources, warm white from incandescent, and warm white (2500 K) from fluorescent sources, which have lower color rendering capabilities. (B) Cool white light sources (4200 K–6500 K) generated better color reproduction for the studied scenarios compared to warm white light sources (2400 K–2700 K). (C) There is a strong connection between the correlated color temperature of a light source and its ability to saturate different color ranges. More detailed, warm white lamps increase the saturation of red and green tones, while cool white lamps do not significantly impact color saturation in any of the studied hues. (D) The results indicate a perceptible connection between the balance of color saturation and subjective color rendition, suggesting that a better balance of saturation leads to higher color rendition.

2. Conclusions

Departing from the groundbreaking advances in the last decades, the research included in the present Editorial covers several fields in lighting. The majority (50%) of the papers concern indoor lighting and factors that affect indoor quality, such as the power quality of LEDs and LED retrofits. Today, we spend about 80% of our time indoors, and in many cases, the workplace is located in a dense urban environment, resulting in the biological effect of natural light being limited. Thus, the examination of the visual performance of users, taking into account the impact of urban groves, was of great importance. Existing technology has greatly reduced the installed power, and thus, the research focus seems to be on the creation of proper products to enhance the power quality of LEDs. Most of the authors made several suggestions for future research. Concerning urban lighting, the author highlights the need for clear and accurate definitions and terminology, innovation and smart technologies, and, finally, the need for an environment-centered design framework with empirical data. Interior lighting research can be enhanced using geometric methods with non-rectangular facilities and more than one model of luminaire. Even the glare in drivers can be a very special issue for research; the adaptation effects and the interaction between the lighting color preference and drivers’ reactions to glare can be further examined. On the subject of the power quality of LEDs, the impact of aging is worthy of investigation. On the subject of daylight, it is crucial to be included when designing sustainable cities; thus, other locations with different insolation conditions and tree species should be adapted in daylight research.