Karin C H J Smolders

• PhD
• Professor (Assistant) at Eindhoven University of Technology

Excessive daytime sleepiness is a common symptom of sleep disorders. Despite its prevalence, it remains difficult to define, detect, and address. The difficulties surrounding sleepiness have been linked to an ambiguous conceptualization, a large variety of scales and measures, and the overlap with other constructs, such as fatigue. The present stud...

Light exposure is an essential driver of health and well-being, and individual behaviours during rest and activity modulate physiologically relevant aspects of light exposure. Further understanding the behaviours that influence individual photic exposure patterns may provide insight into the volitional contributions to the physiological effects of...

Background There is no consensus on reporting light characteristics in studies investigating non-visual responses to light. This project aimed to develop a reporting checklist for laboratory-based investigations on the impact of light on non-visual physiology. Methods A four-step modified Delphi process (three questionnaire-based feedback rounds a...

Objective This study examined whether daily safe, low-dose ultraviolet-B (UVB) exposure using a home-based lighting solution could maintain healthy serum 25(OH)D during winter. Methods Twenty-eight (12 male, 16 female) daytime (~9:00 to 17:00) indoor workers (mean age = 42.46; SD = 14.23) participated in this study and were allocated to one of the...

Light exposure is an essential driver of health and well-being, and individual behaviours during rest and activity modulate physiologically-relevant aspects of light exposure. Further understanding the behaviours that influence individual photic exposure patterns may provide insight into the volitional contributions to the physiological effects of...

Background Light exposure is an important driver and modulator of human physiology, behavior and overall health, including the biological clock, sleep-wake cycles, mood and alertness. Light can also be used as a directed intervention, e.g., in the form of light therapy in seasonal affective disorder (SAD), jetlag prevention and treatment, or to tre...

Anecdotal evidence suggests that the correlated color temperature (CCT) of light can affect thermal comfort. Previous literature mostly investigated this effect over a short duration (<1 h) and often attributed it to the hue-heat hypothesis (color-temperature association), which posits that the visual experience of blue colors (high CCT) results in...

Dynamic lighting is a potentially promising solution to meet the individual's chronobiologic and psychological needs at specific times of day or for specific activities. Yet, few studies have investigated the impact of dynamic lighting patterns on daytime functioning and nocturnal sleep, and the optimal dynamic lighting pattern remains largely unkn...

Intermittent bright light during the night has shown to be able to generate circadian phase-shifting effects, suppress melatonin and induce alertness, but little attention has been devoted to the effects of diurnal intermittent bright light. Following a night of sleep restriction, forty participants were exposed in a counterbalanced within-subject...

Highlights the study design investigating daytime effects of light with metameric light designs using existing and novel EEG methods.

Background: Sleep is an important determinant of individuals' health and behavior during the wake phase. Novel research methods for field assessments are required to enable the monitoring of sleep over a prolonged period and across a large number of people. The ubiquity of smartphones offers new avenues for detecting rest-activity patterns in ever...

BACKGROUND Sleep is an important determinant of individuals’ health and behavior during the wake phase. Novel research methods for field assessments are required to enable the monitoring of sleep over a prolonged period and across a large number of people. The ubiquity of smartphones offers new avenues for detecting rest-activity patterns in everyd...

Light exposure is an important driver of health and well-being. Many aspects of light exposure are modulated by our behaviour. How these light-related behaviours can be shaped to optimise personal light exposure is currently unknown. Here, we present a novel, self-reported and psychometrically validated instrument to capture light exposure-related...

In this field study, we tested the effects of dynamic light scenarios and personal illuminance on visual experience, sleepiness, cognitive performance and sleep in an operational office. Two dynamic light scenarios, different in timing but with equal luminous exposure, were tested against a reference scenario in a counterbalanced crossover design....

Throughout the day, we are exposed to light that varies drastically over time. Correct quantification of the light is important when predicting sleep and subjective alertness in the field, yet doing so, is a complex challenge. In the current manuscript, we explore the feasibility of a novel, practical method to quantify light exposure, based on the...

Background: Light exposure is essential for our health and well-being, driving various non-visual processes, including circadian photoentrainment, melatonin suppression and the modulation of alertness. An unexplored dimension of light exposure is that it is partially controlled by our behaviour. Here, we present a novel instrument to capture light...

Human cognitive functioning shows circadian variations throughout the day. However, individuals largely differ in their timing during the day of when they are more capable of performing specific tasks and when they prefer to sleep. These interindividual differences in preferred temporal organization of sleep and daytime activities define the chrono...

Introduction Rest-activity patterns are important aspects of healthy sleep and may be disturbed in conditions like circadian rhythm disorders, insomnia, insufficient sleep syndrome, and neurological disorders. Long-term monitoring of rest-activity patterns is typically performed with diaries or actigraphy. Here, we propose a fully unobtrusive metho...

Detailed insights in both visual effects of light and effects beyond vision due to manipulations in illuminance and correlated color temperature (CCT) are needed to optimize study protocols as well as to design light scenarios for practical applications. This study investigated temporal dynamics and interindividual variability in subjective evaluat...

Rest–activity patterns are important aspects of healthy sleep and may be disturbed in conditions like circadian rhythm disorders, insomnia, insufficient sleep syndrome, and neurological disorders. Long‐term monitoring of rest–activity patterns is typically performed with diaries or actigraphy. Here, we propose an unobtrusive method to obtain rest–a...

Given the fact that most office workers spend substantial parts of their working day – and life – indoors, it is important to provide healthy conditions in the office. An important factor in this respect is lighting. Many laboratory studies have investigated acute effects of light on people’s alertness and cognitive performance, as well as effects...

Literature has occasionally reported acute effects of office illuminance on cognitive performance during daytime. The current study was conducted to systematically investigate whether the type of task and level of task difficulty moderate the effect of daytime illuminance on cognitive functioning. Thirty healthy participants were assigned to high (...

Detailed insights in both visual effects of light and effects beyond vision due to manipulations in illuminance and correlated color temperature (CCT) are needed to optimize study protocols as well as to design light scenarios for practical applications. This study investigated temporal dynamics and interindividual variability in subjective evaluat...

The use of dynamic light scenarios for indoor environments may be motivated by the aim to support our circa-dian rhythms or provide a fascinating and/or informative environment. Additionally, dynamic lighting may be beneficial as it could acutely provide support at certain times of day, or for specific tasks or activities. A systematic literature s...

Providing more diurnal light to people working indoors serves vitality and healthy entrainment of our internal clock via the non-image forming pathway. But we do not exactly know how much light people are exposed to in their office, nor do we know how much extra light they receive if we raise the overall illuminance. In this study, we tracked offic...

Vitamin D insufficiency is common in the healthy population. Recent insights addressed the role of vitamin D in serotonin and melatonin regulation, suggesting that increasing vitamin D status may be helpful for improving mood and sleep. This literature review covers the current state of evidence regarding potential effects of vitamin D on mood and...

Knowledge on the onset, persistence, and symmetry of effects of lighting transitions on humans is relevant when designing dynamic lighting scenarios and, additionally, can shed light on the dominance of underlying mechanisms. We examined temporal trajectories in measures of alertness, arousal and comfort after abrupt lighting transitions that were...

More than one third of a buildings' energy consumption is designated for heating and cooling. Therefore, allowing more variations in the indoor temperature provides an energy saving potential. Additionally, these variations are expected to have beneficial health effects on the building occupants. To compensate for potential discomfort amongst them...

Background: Studies suggest that light and nature should be seriously considered when building new psychiatric clinics, because of their positive effects on psychiatric recovery. AIM: To highlight positive and sustainable effects of light and greenery in mental health care. METHOD: Literature study. RESULTS: Daylight, artificial light and nature m...

Light is known to elicit non–image-forming responses, such as effects on alertness. This has been reported especially during light exposure at night. Nighttime results might not be translatable to the day. This article aims to provide an overview of (1) neural mechanisms regulating alertness, (2) ways of measuring and quantifying alertness, and (3)...

To date, it is largely unknown which light settings define the optimum to steer alertness and cognitive control during regular daytime working hours. In the current article, we used a multimeasure approach combined with a relatively large sample size (N = 60) and a large range of intensity levels (20-2000 lux at eye level) to investigate the dose-d...

Research has explored acute effects of light level and correlated color temperature (CCT) of indoor lighting on subjective measures of alertness and task performance during daytime. Yet, these investigations did not render a conclusive or consistent finding on the relative contribution of illuminance and CCT on various cognitive domains. The curren...

supplementary_materials_-_dose-response_relationships_for_effects_of_white_light_exposure – Supplemental material for Investigation of Dose-Response Relationships for Effects of White Light Exposure on Correlates of Alertness and Executive Control during Regular Daytime Working Hours

Chronotype questionnaires provide a simple and time-effective approach to assessing individual differences in circadian variations. Chronotype questionnaires traditionally focused on one dimension of chronotype, namely its orientation along a continuum of morningness and eveningness. The Caen Chronotype Questionnaire (CCQ) was developed to assess a...

To facilitate a better understanding of the role of self-control capacity in self-control processes, we examined its variation at intraindividual and interindividual levels, and positioned it in a nomological network with core affect. In two experience sampling studies, 286 university students reported their self-control capacity and core affect fo...

To facilitate a better understanding of the role of self-control capacity in self-control processes, we examined its variation at intraindividual and interindividual levels, and positioned it in a nomological network with core affect. In two experience sampling studies, 286 university students reported their self-control capacity and core affect fo...

This study investigated seasonal and time-of-day dependent moderations in the strength and direction of acute diurnal non-image forming (NIF) effects of illuminance level on performance, physiology, and subjective well-being. Even though there are indications for temporal variations in NIF-responsiveness to bright light, scientific insights into po...

Research in the late evening and at night has shown that acute activating effects of light are particularly sensitive to short-wavelength light. Yet, findings on such effects during daytime are still inconclusive. This study (N = 39) investigated effects of correlated colour temperature (CCT; 2700 K vs. 6000 K, 500 lx on the desk) on individuals' e...

This study investigated diurnal non-image forming (NIF) effects of illuminance level on physiological arousal in parallel to NIF effects on vigilance and working memory performance. We employed a counterbalanced within-subjects design in which thirty-nine participants (mean age = 21.2; SD = 2.1; 11 male) completed three 90-min sessions (165 vs. 600...

This study examined whether diurnal non-image forming (NIF) effects of illuminance level on cognitive task performance depend on task difficulty and time of day. We employed a balanced crossover design with two 60-minute sessions of 200 vs.1000 lux at eye level. Digit-span task difficulty was manipulated within subjects (forward (FDST) vs. backward...

We investigated the effect of exposure to bright white light as compared to a commonly experienced illuminance (1000 lx vs. 200 lx at eye level, 4000 K) on electroencephalography spectral power density during daytime. Spectral power density was measured during one hour of exposure in the morning and in the afternoon. Results showed a lower relative...

Alertness-enhancing effects of bright light are particularly strong at night or after sleep deprivation. Alerting effects during daytime also exist, yet these appear to be more modest. In this study, we investigate whether a higher illuminance level particularly benefits individuals who suffer from mental fatigue – not from sleep pressure, but from...

This research motivates and evaluates the notion of similarity awareness as a means to enhance connectedness between remote family members. Similarity awareness refers to notifying connected individuals when they are engaged in similar activities. This idea is illustrated with the design and evaluation of MatchMaker an application targeting the nee...

It is hard to overestimate the importance that light has for the human condition. From the comforting atmosphere of a quietly lit living room, to the invigorating effects of morning light, preparing you for your day, light has dramatic effects on mood, health and pro-ductivity, and can deeply influence the way we experience an environment. Biologis...

Dynamic lighting is designed to have positive effects on well-being and performance. In a field experiment we tested whether these effects are detectable and stable over time when employed in actual work settings. The study consists of two tranches, one following a monthly alternating experimental design, the other a yearly alternating one. This pa...

Social connectedness, that is, the experience of belonging and relatedness between people, is a central concept in understanding and evaluating mobile communication media. This paper describes a laboratory experiment where we examined the effects of I-sharing on social connectedness and its dimensions. I-sharing is a special form of shared subjecti...

Social connectedness, i.e. the experience of belonging and relatedness between people, is a central concept in understanding and evaluating communication media, in particular awareness systems. A generic measure based on this construct can support the design of such systems. The current paper describes the construction of two questionnaires for the...