Luminaires, Photometrics and Object-Scale Lighting

In recent years, increasing attention has been directed towards renewable energy sources as part of the global effort to address environmental challenges and energy crises. While established technologies such as solar, wind, and hydropower continue to dominate in this energy landscape, growing interest has been observed in the exploration of non-conventional and emerging systems operating at micro-scale power levels, intended for specific low-energy applications rather than large-scale energy production. Among these, Plant Microbial Fuel Cells (PMFCs) represent a promising yet still underexplored technology. Rooted in natural biological processes, PMFCs enable electricity generation by harvesting electrons released during plants’ photosynthesis. Organic compounds released by roots in the soil are decomposed by microorganisms, releasing electrons; the latter can be captured by fuel cell’ electrodes and converted into electrical energy. In this non-invasive process, the electrical output is closely linked to the physiological condition of the plant, making the plant not only an energy source but also a potential indicator of its health. In this study, PMFC technology is investigated beyond its purely technical and functional dimension, exploring its potential as a driver for design innovation and as a medium for rethinking the role of light. Two identical patented PMFC units developed by the leading company in the field, Plant-E, to two distinct environmental contexts: controlled and uncontrolled environmental settings. The study investigates and compares the two contexts performance, and it highlights the correlation between biological processes, energy generation, and environmental conditions. Accordingly, two scenarios are defined: a conventional plant-in-pot system, representing a less controlled and more exposed setting, and a terrarium-based system, characterised by enhanced environmental control and stability. The adoption of a terrarium configuration, consisting of a small-scale enclosed system, is proposed to address key limitations associated with conventional PMFC applications, including environmental instability, exposure to external disturbances, and the need for frequent maintenance and irrigation. Performance is evaluated through the monitoring of key environmental and electrical parameters, including: (i) soil and air temperature, (ii) soil moisture content, and (iii) output voltage measured directly at the system input terminals, to assess the effective generation prior to its interaction with downstream electronic components. The results revealed significant performance differences between the two environments, with the terrarium-based system exhibiting higher voltage outputs, in the order of millivolts (mV), than the plant-in-pot configuration, indicating enhanced electrical performance under more controlled conditions. In addition to the quantitative data, qualitative observations further strengthened these findings, revealing that plants within the terrarium were visibly healthier and more vigorous, as evidenced by greater leaf turgidity and uprightness, increased foliage density, and more robust stem development. This experimental phase is established as the basis for a subsequent design-oriented phase, intended to support future lighting design applications. In this context, the terrarium configuration is interpreted not only as an experimental setup but also as a potential design strategy aimed at optimising the environmental conditions in which the system operates. Accordingly, the focus of the future design-oriented phase will be shifted from optimisation of the device itself to the optimisation of the environmental conditions in which the device operates. Future design-oriented research will not focus on increasing the energy output of the system, but rather on developing lighting solutions capable of operating within its current energy range. Potential applications within public spaces include small-scale urban interventions, where light is not required to perform high-intensity illumination but can contribute to atmosphere, orientation, and environmental awareness. The vision is to enable off-grid lighting systems that rely on biologically generated electricity, effectively deriving energy directly from plant-based processes.

Introduction

Temporal Light Modulation (TLM) describes the fluctuations in luminous or chromatic output over time from light sources. It gives rise to visual artefacts such as flicker, stroboscopic effects and the phantom array effect, which degrades light quality, visual performance and modifies brain activity and task performance. For sensitive people it is responsible for headaches, eyestrain, general discomfort during and after exposure and epileptic seizures can be cause by direct flicker and flashes. TLM is caused by the driver electronics and mains supply, and high levels can be fixed at the product level by lighting manufacturers through improved electrical design. Therefore, proper limits should be set to protect sensitive people.

Flicker can be perceived at frequencies up to approx. 80 Hz and is caused by periodic and non-periodic variations as random or transient fluctuations of the light. It is characterised by the short-term flicker visibility index, PstLM, defined by IEC TR 61547, and regulations are in place in EU since 2021 with a maximum allowable value for PstLM of 1, however only for mains LED light sources and only at full load. New research suggest that the visibility threshold is in fact lower than 1 and it has been shown that large uncertainties in the measurement of PstLMarise from the AC power supply used to operate the LED light source under measurements. The latter was an important result of the IC2023 interlaboratory comparison of TLM measurements carried out by the IEA 4E SSL Annex, which also showed large variations in the other flicker metric perceptual modulation MP. Here the found uncertainties of the intrinsic PstLMmetric are investigated related to actual consumer mains connection, and further it is compared to a redefinition of MP.

Methods

Nineteen laboratories participated in the IC2023 and measured the same four LED lamp artefacts, and a halogen artefact. This has provided an extensive and substantial dataset of TLM quantities and raw waveform data combined with knowledge of the measurement configurations used by the laboratories, including the AC power supply. This makes it possible to redo and make new calculations on the waveforms at 20 kHz sampling and a 180 s duration necessary for PstLM calculation. Based on the IC2023 results, a corrected and redefinition of MP, called MP,26which only requires 5 s measurement duration has been thoroughly investigated with regards to measurement uncertainty and compared to MP and PstLM. Further an investigation of the intrinsic measure PstLM through immunity test and actual measurements when the LED artefacts are connected to mains outside laboratory is performed.

Findings and discussion

The variation of PstLM due to AC power supplies is shown to be up to 0.3. This is very large compared to the preliminary estimates of visual threshold of ~0.5. For MP,26the value is ~1.4, and the initial results show that the MP,26 variations due to the used AC power supplies are about half of PstLM if MP,26 is rescaled for a new sensitivity function. The ratio of visual threshold and variation due to AC power supply is found to be a factor of 3 better. The analysis must be related to new ongoing experimental investigations of visual thresholds for the flicker metrics.

Conclusions

Based on the extensive dataset of TLM quantities and raw waveform data, the flicker metrics, PstLM, MP, and redefined MP,26 has been analysed and compared with respect to measurement uncertainty and visual threshold values. It may lead to an improved flicker metric easier to measure and with better relation between, the visual threshold, regulated limit value and measurement uncertainty.

This study explores the potential of biobased composite materials as task lighting interfaces through the interconnected dimensions of materiality, environmental performance, and multisensory experience. In lighting fixture design, materials are often treated as passive components that support luminous performance. This research instead approaches biobased composites as active mediators of light, capable of shaping how light is diffused, transmitted, and spatially perceived in office interiors. Focusing on the interaction between light and naturally derived material surfaces, the study examines how such materials may contribute to a multisensory reading of office interiors while supporting more sustainable and ecologically responsive design approaches.

A series of biocomposite samples was produced using natural ingredients, resulting in translucent and transparent surfaces with varying textures, densities, and light transmission properties. The study adopted a comparative material-based evaluation, examining the samples as potential lighting interfaces rather than static material specimens, and comparing them with a single-material lighting source with a polycarbonate (PC) fixture. Their interaction with light was investigated under controlled artificial lighting conditions through illuminance measurements, photographic documentation, and qualitative material characterization. Light transmission was assessed by measuring illuminance values before and after the samples, while diffusion performance was evaluated through the spatial distribution of transmitted light across multiple measurement points. In addition, material thickness and density were documented quantitatively, while surface texture and related material qualities were assessed qualitatively to examine how physical variation influenced visual softness, atmospheric effect, and light-filtering capacity.

The findings indicate that biocomposite surfaces can significantly influence the character of light in interior settings when compared to a single-material lighting source with a PC fixture. Most samples softened and redirected artificial light, reducing visual harshness and producing more diffuse luminous conditions. Variations in texture, translucency, and density affected the spread and depth of light, generating layered visual effects across the material surfaces. Beyond their optical performance, the samples also contributed to a multisensory reading of space by revealing organic textures, material irregularities, and atmospheric qualities that extended the experience of light beyond illumination alone.

These results suggest that biobased composites may be understood not only as sustainable alternatives to conventional lighting materials, but also as performative design media that shape spatial perception. Their capacity to mediate light through material variation introduces a more experimental and materially expressive approach to lighting design, in contrast to standardized industrial diffusers. In this sense, the study highlights the value of integrating natural material processes into lighting applications where atmosphere, sensory richness, and ecological awareness are central. It also points to the potential of biobased materials to expand current discussions on interior lighting by linking luminous performance with material agency and environmental sensitivity.

The study concludes that biobased composite materials hold strong potential as lighting interfaces for interior design through their ability to soften, filter, and redirect light, so that they can support more adaptive and environmentally responsive luminous environments while enriching the sensory and atmospheric qualities of space. By bringing together ecological material processes and lighting design, the research proposes an alternative framework in which light is experienced through the performative and expressive capacities of biobased matter.

Visibility is a fundamental element for describing the visual environment in architecture and urban spaces. Yoshizawa et al. (2021) developed an edge detection algorithm that reproduces early visual processing based on neurophysiological mechanisms to estimate visibility under photopic conditions. Subsequently, with the introduction of a cone response model (De Valois et al., 1993), the algorithm was reconstructed to represent processing from the retina to the lateral geniculate nucleus (LGN) based on L-, M-, and S-cone responses. Visibility changes as humans acquire visual information under various luminance conditions and adapt to their environment. However, the current algorithm does not fully account for the observer’s light-adaptation state, and challenges remain in its application to real-world lighting environments. In this study, we investigated the edge detection algorithm by incorporating a mechanism that mimics changes in the bleaching of LMS cones according to adaptation, adjusting the semi-saturation constants of each cone. The algorithm was validated through subjective evaluation experiments on the visibility of edges under different adaptation conditions.

In the experiment, each participant (n = 18) first dark-adapted for 10 minutes. Subsequently, with their chins placed at rest, they adapted for 250 seconds to a uniform luminance within a white hemispheric space with a radius of approximately 350 mm. The adaptation and background luminances were set to 20, 60, and 200 cd/m², respectively. An evaluation target (visual field angle of 10 degrees) comprising two regions with different luminances was presented for one second against each background. During a 30-second readaptation period, the visibility of the edge between the regions was rated on a 6-point scale (evaluation range: 2-degree field of view). The evaluation targets included positive and negative contrast against the background, with luminance ratios at the edge set to 1.05, 1.05^3, and 1.05^6. The presentation order was organised into blocks for each adaptation condition and randomised within each block. The cycle of readaptation and presentation was repeated, and when changing adaptation conditions, a 250-second adaptation period was conducted.

The results showed that, under the conditions set for this study, the ratings of edge visibility did not vary significantly with adaptation luminance. Furthermore, regardless of adaptation or background luminance, there was no significant difference between the positive and negative contrasts.

Variations in the evaluations were observed when the participants adapted to 200 cd/m². Under these conditions, for all the luminance ratios, the visibility ratings tended to be higher when the background luminance was close to the adaptation luminance. A contrast ratio of 1.05 was close to the perceptual threshold. Sensitivity might have changed due to adaptation, with reduced neural noise potentially enhancing edge visibility at this contrast level. However, this explanation does not account for the results at other luminance ratios, and the mechanism remains unclear.

These findings suggest that the effects of adaptation need not be strongly considered when making rough predictions of edge perception under achromatic conditions. However, as these results are limited to the luminance range used in this experiment, further validation across a wider luminance range is necessary, particularly for applications in edge perception prediction in outdoor environments.

In the future, we aim to deepen our understanding of the mechanisms underlying changes in visibility due to adaptation at the threshold and suprathreshold levels and explore potential mechanisms for incorporation into the algorithm. The results of this study are expected to be useful for evaluating and designing visual environments in real-world spaces.

Introduction

Glare arising from both daylight (including direct sunlight) and electric lighting is widely recognised as one of the most persistent and complex challenges in lighting research. Its effects extend beyond visual discomfort, contributing to occupational health concerns, reduced productivity, and inefficient allocation of energy and financial resources toward lighting and façade solutions that fail to provide adequate visual conditions. Physiological responses to glare—such as pupil constriction, squinting, and retinal adaptation—reduce the amount of light reaching the retina. As a result, an inherent trade-off emerges between illumination and visual usability: as glare increases, the proportion of light that is functionally beneficial for visual tasks decreases.

Glare is fundamentally a physiological response to luminance contrasts within the visual field, occurring when specific light sources exhibit luminance levels significantly higher than the eye’s state of adaptation. Its impact ranges from mild visual discomfort to severe visual impairment, potentially creating hazardous conditions in environments such as transportation systems and industrial settings. In office environments, excessive glare has been linked to visual fatigue, headaches, and decreased work performance, leading to substantial—though often difficult to quantify—productivity losses.

Despite decades of research, glare remains difficult to simulate and measure due to its complex physiological basis. Existing glare assessment methods, such as UGR and DGI, rely on simplifying assumptions—most notably that luminance is uniformly distributed across light-emitting surfaces. This assumption often fails for modern luminaires with highly non-uniform luminance distributions. Efforts to address this limitation, such as the introduction of a correction factor in CIE 232, have improved theoretical accuracy but have not achieved widespread adoption. This is likely due to the reliance on expensive imaging luminance measurement devices (ILMDs) and the practical tendency within industry to prioritise lower glare index values rather than more precise characterisation.

ILMD-based glare analysis can be applied in both laboratory and real-world environments, enabling the derivation of glare metrics such as UGR, DGI, and TI from luminance maps. However, fundamental challenges persist. There is still no unified model capable of accurately describing glare across different contexts, including indoor daylighting, electric lighting, and outdoor applications such as street lighting. Consequently, the field lacks a comprehensive framework for interpreting luminance data and predicting glare perception.

Methods, Findings and Discussion

The novel and patented technique presented here introduces a new approach to luminance analysis. It integrates an advanced ILMD camera with a spectrometer sensor, enabling the simultaneous capture of radiance distribution video and standard light intensity measurements. This system automatically detects luminance patterns across all viewing angles within a single measurement process, significantly enhancing analytical detail without increasing measurement time. The technique integrated in a goniospectrometric laboratory systems, allowing parallel acquisition of conventional intensity distributions (C-γ) alongside full-field luminance imaging. Furthermore, it supports high dynamic range (HDR) image capture in critical directions and enables advanced analyses, including blue light hazard classification and the generation of luminance and radiance heat maps.

Conclusions

This method is a significant step toward a more comprehensive understanding of glare because of detailed viewing-angle dependent luminance imaging. It provides a richer dataset for analyzing complex luminance distributions and establishes a foundation for developing more accurate, universally applicable glare models. Such models may potentially replace existing glare indices with advanced image processing, applying to both real and simulated spaces. Ultimately, this approach has the potential to transform glare evaluation in research and practice, by supporting future research projects and standardisation with unprecedented data.

With the development of LED technology, light is increasingly integrated into

products that previously were not illuminated to create newness rather than adding

technical functions. However, in the field of lighting design, knowledge is still mainly

structured around spatial, theatrical, and architectural conditions. Leaving a research gap

on how product integrated light can be analysed. This paper explores an initial artefact_x0002_scale approach by translating selected spatial-scale mobility concepts to the analysis of

products with integrated light.

The paper combines a scoping-oriented literature review with an initial observational photo

study. The concept of Mobility was selected as a first criterion to explore the translation of

knowledge from architectural to product lighting design. The photo study uses the methods

analytical mapping and template-guided visual analysis to examine how Mobility related

conditions appear across integrated light artefacts.

The findings show that Mobility in lighting is dependent on several interacting conditions;

users and artefact movement, proximity, viewing position, activation, environmental use

conditions, and the spatial impact of light. The result is a proposed light design typology

that oOers an analytical guideline when examining light features and functions in relation to

the product experience in an industrial design process.