Julian Kunkel

Bio: Julian Kunkel is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 1 citations.

Measurement of Circadian Effectiveness in Lighting for Office Applications

Abstract: As one factor among others, circadian effectiveness depends on the spatial light distribution of the prevalent lighting conditions. In a typical office context focusing on computer work, the light that is experienced by the office workers is usually composed of a direct component emitted by the room luminaires and the computer monitors as well as by an indirect component reflected from the walls, surfaces, and ceiling. Due to this multi-directional light pattern, spatially resolved light measurements are required for an adequate prediction of non-visual light-induced effects. In this work, we therefore propose a novel methodological framework for spatially resolved light measurements that allows for an estimate of the circadian effectiveness of a lighting situation for variable field of view (FOV) definitions. Results of exemplary in-field office light measurements are reported and compared to those obtained from standard spectral radiometry to validate the accuracy of the proposed approach. The corresponding relative error is found to be of the order of 3–6%, which denotes an acceptable range for most practical applications. In addition, the impact of different FOVs as well as non-zero measurement angles will be investigated.

A Randomized Controlled Trail for Comparing LED Color Temperature and Color Rendering Attributes in Different Illuminance Environments for Human-Centric Office Lighting

Abstract: In this study, two experiments were conducted to investigate the effects of the color rendering index (CRI) and correlated color temperature (CCT) of light-emitting diode (LED) lighting on office user acceptance and to explore the proper color attributes for human-centric office lighting. Experiment 1 had four LED lights, with two levels for the CRI (CRI < 80: 79, 76; or CRI ≥ 80: 83, 84) and CCT (3000 K or 6500 K) at 300 lux. In experiment 2, there were four LED lights, with several levels for the CRI (CRI < 80: 78; or CRI ≥ 80: 87, 83) and CCT (3000 K or 6500 K) at 500 lux. Ninety-six participants in experiment 1 and ninety-four participants in experiment 2 performed a reading task. The results in experiment 1 and experiment 2 showed that LEDs with lower CRI values at warm color temperatures were rated as more acceptable than LEDs with higher CRI values at warm color temperatures. However, the positive effect extended to LEDs with higher CRI values at cool temperatures but not to LEDs with lower CRI values at cool temperatures. Therefore, the findings are that LEDs with lower CRI values at warm color temperatures and LEDs with higher CRI values at cool temperatures provide the right level of color attributes for office lighting.

The Necessity for Multi-Spectral Simulations of the Indoor Non-Visual Luminous Environment: A Simplified Annual Approach

Abstract: The difference between the functioning of the human non-visual and photopic systems has elicited the need for complex in situ measurements or time-consuming multi-spectral simulations to accurately predict the non-visual luminous content of the indoor environment. As such methodologies are time-consuming, the aim of the present study was to determine whether such complex methodologies are needed. The issue was studied through simulations of four cardinally oriented identical offices located in Ljubljana, Slovenia. Each was studied using orange, grey and blue walls. Diurnal luminous conditions were studied under clear, hazy and overcast skies on December, March and June 21st. The non-visual content was evaluated using novel metrics, the Autonomy of Circadian Potential and Circadian Autonomy, which assess temporal circadian luminous content. Diurnal results were used to construct climate-based spectral months to evaluate the monthly non-visual potential of the studied offices. Furthermore, simulations addressed the question of whether the requirements of the non-visual system might contradict the visual comfort of indoor environments. The results show that compliance with non-visual requirements for indoor spaces with spectrally neutral surfaces or those in shades of blue could be assessed using photopic methodologies. However, this is not true for spaces characterised by orange and red materials.

Processing RGB Color Sensors for Measuring the Circadian Stimulus of Artificial and Daylight Light Sources

Abstract: The three main tasks of modern lighting design are to support the visual performance, satisfy color emotion (color quality), and promote positive non-visual outcomes. In view of large-scale applications, the use of simple and inexpensive RGB color sensors to monitor related visual and non-visual illumination parameters seems to be of great promise for the future development of human-centered lighting control systems. In this context, the present work proposes a new methodology to assess the circadian effectiveness of the prevalent lighting conditions for daylight and artificial light sources in terms of the physiologically relevant circadian stimulus (CS) metric using such color sensors. In the case of daylight, the raw sensor readouts were processed in such a way that the CIE daylight model can be applied as an intermediate step to estimate its spectral composition, from which CS can eventually be calculated straightforwardly. Maximal CS prediction errors of less than 0.0025 were observed when tested on real data. For artificial light sources, on the other hand, the CS approximation method of Truong et al. was applied to estimate its circadian effectiveness from the sensor readouts. In this case, a maximal CS prediction error of 0.028 must be reported, which is considerably larger compared to daylight, but still in an acceptable range for typical indoor lighting applications. The use of RGB color sensors is thus shown to be suitable for estimating the circadian effectiveness of both types of illumination with sufficient accuracy for practical applications.

Modeling the influence of nighttime light on melatonin suppression in humans: milestones and perspectives

Abstract: This review presents the main metrics developed so far to correlate physical properties of light and its effects on melatonin suppression. Melatonin is a hormone secreted at night and its production is suppressed by exposure to light. In this context, the negative effects of lighting at night and high exposure to light raise the need for a better quantification of these impacts on health. Different light action spectroscopy methodologies have been recently used to characterize the circadian response mediated by melatonin in humans, but there is so far no consensus on a main validated model. While complementary studies are still necessary to reach such an ideal model, here we analyze and compare the results of works that developed and tested metrics based on the absorption curves of human melanopsin, rods and cones, and on the dynamics of melatonin suppression in different light regimes. These studies reveal how the spectral composition, irradiance and temporality of light modulate the function of human melatonin. We present milestones in this research field, together with discussion on the advances, limitations and perspectives of application for distinct available models. Applied to different contexts, this knowledge can bring favorable changes to health in environmental lighting projects, production of ophthalmic lenses, screens, filters, films, and other optical devices.

Study protocol for measuring the impact of (quasi-)monochromatic light on post-awakening cortisol secretion under controlled laboratory conditions

Abstract: Cortisol secretion has a fundamental role in human circadian regulation. The cortisol awakening response (CAR) can be observed as a daily recurring sharp increase in cortisol concentration within the first hour after awakening and is influenced by environmental light conditions. The current work provides the study protocol for an ongoing research project that is intended to explore the spectral dependencies and to discuss measures of emotional state and cognitive functioning potentially related to the CAR. Based on a controlled within-subjects sleep laboratory study, the impact of a two-hour, (quasi-)monochromatic, post-awakening light exposure of different peak wavelength (applied from 6:00 to 8:00 am) on resulting CAR levels should be investigated in a systematic manner to eventually derive a corresponding spectral sensitivity model. As a secondary outcome, it should be explored whether a potentially light-enhanced cortisol secretion might also impact different measures of sleepiness, mood, and vigilance for certain wavelengths. The study protocol described in the present work discusses the various protocol steps using pilot data collected for two different wavelength settings (i.e., short-wavelength blue-light at λmax = 476 nm and long-wavelength red-light at λmax = 649 nm) experienced by a group of four healthy male adults at an average ± SD age of 25.25 ± 3.59 years.