K.C.H.J. Smolders

Seasonal and time-of-day variations in acute non-image forming effects of illuminance level on performance, physiology, and subjective well-being

ABSTRACT 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 potential moderations by season are scarce. We employed a 2 (Light: 165 versus 1700 lx at the eye level, within) × 2 (Season: autumn/winter versus spring, between) × 2 (Time of day: morning versus afternoon, between) mixed-model design. During each of the two 90-min experimental sessions, participants (autumn/winter: N = 34; spring: N = 39) completed four measurement blocks (incl. one baseline block of 120 lx at the eye level) each consisting of a Psychomotor Vigilance Task (PVT) and a Backwards Digit-Span Task (BDST) including easy trials (4–6 digits) and difficult trials (7–8 digits). Heart rate (HR) and skin conductance level (SCL) were measured continuously. At the end of each lighting condition, subjective sleepiness, vitality, and mood were measured. The results revealed a clear indication for significant Light * Season interaction effects on both subjective sleepiness and vitality, which appeared only during the morning sessions. Participants felt significantly more vital and less sleepy in winter, but not in spring during bright light exposure in the morning. In line with these subjective parameters, participants also showed significantly better PVT performance in the morning in autumn/winter, but not in spring upon bright light exposure. Surprisingly, for difficult working memory performance, the opposite was found, namely worse performance during bright light exposure in winter, but better performance when exposed to bright light in spring. The effects of bright versus regular light exposure on physiology were quite subtle and largely nonsignificant. Overall, it can be concluded that acute illuminance-induced NIF effects on subjective alertness and vitality as well as objectively measured vigilance in the morning are significantly moderated by season. Possibly, these greater illuminance-induced benefits during the morning sessions in autumn/winter compared to spring occurred due to increased responsiveness to bright light exposure as a function of a relatively low prior light dose in autumn/winter.

Investigation of Dose-Response Relationships for Effects of White Light Exposure on Correlates of Alertness and Executive Control during Regular Daytime Working Hours

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-dependent relationship between light and correlates of alertness and executive control during regular working hours in the morning and afternoon. Each participant was exposed to a single-intensity light level for 1 h after a 30-min baseline phase (100 lux at the eye) in the morning and afternoon (on separate days) during their daily routine. Results revealed no clear dose-dependent relationships between 1-h daytime light exposure and correlates of alertness or executive control. Subjective correlates showed only very modest linear relationships with the log-transformed illuminance, and we found no significant effects of light intensity on the behavioral and physiological indicators. Overall, these results suggest that daytime exposure to more intense light, at least for 1 h of exposure, may not systematically benefit alertness or executive functioning. However, future research is required to investigate effects of longer exposure durations and potential moderations by prior light exposure, personal characteristics, and spectrum.

Light, Alertness, and Alerting Effects of White Light: A Literature Overview

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) the current literature specifically regarding effects of different intensities of white light on various measures and correlates of alertness during the daytime. In general, the present literature provides inconclusive results on alerting effects of the intensity of white light during daytime, particularly for objective measures and correlates of alertness. However, the various research paradigms employed in earlier studies differed substantially, and most studies tested only a limited set of lighting conditions. Therefore, the alerting potential of exposure to more intense white light should be investigated in a systematic, dose-dependent manner with multiple correlates of alertness and within one experimental paradigm over the course of day.

Convergent and construct validity and test-retest reliability of the Caen Chronotype Questionnaire in six languages

ABSTRACT 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 an additional dimension of chronotype that captures the extent to which individual functioning varies during the day (amplitude). The aim of this study was to provide a multilanguage validation of the CCQ in six world regions (Arabic, Dutch, German, Italian, Portuguese and Spanish). At Time 1, a total of 2788 participants agreed to take part in the study (Arabic, n = 731; Dutch, n = 538; German, n = 329; Italian, n = 473; Portuguese, n = 361; Spanish, n = 356). Participants completed an assessment of the CCQ together with the Morningness-Eveningness Questionnaire (MEQ; Horne & Ostberg 1976) as well as questions related to factors theoretically related to chronotype (age, shift work, physical activity, sleep parameters and coffee consumption). One month later, participants again completed the CCQ. Results showed that the two-factor structure (morningness-eveningness and amplitude) of the CCQ could be replicated in all six languages. However, measurement invariance could not be assumed regarding the factor loadings across languages, meaning that items loaded more on their factors in some translations than in others. Test–retest reliability of the CCQ ranged from unacceptable (German version) to excellent (Dutch, Portuguese). Convergent validity was established through small–medium effect size correlations between the morningness-eveningness dimension of the CCQ and the MEQ. Taken together, our findings generally support the use of the translated versions of the CCQ. Further validation work on the CCQ is required including convergent validation against physiological markers of sleep, health and well-being.

Editorial : experiencing light

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 productivity, and can deeply influence the way we experience an environment. Biologists acknowledge the powerful influence that Earth’s 24-hour light–dark cycle has on the behaviour and physiology of animals and humans that have evolved on this planet. Psychiatrists and clinical psychologists, treating patients for sleep disorders or seasonal affective disorders, can attest to the importance of light for psychological well-being. Human factors professionals, too, recognise light as a significant factor in people’s health, performance and safety in a variety of contexts, including factories, offices, schools and homes. Artists – from Golden Age painters to modern day cineasts – all have been keenly aware of the aesthetic and emotional impact light has on our experience of art; its power to create mood, suspense and mystery, to capture our gaze and to challenge our curiosity. Similarly, in architecture and urban planning, the importance of getting the lighting right, whether from natural or artificial sources, is generally acknowledged. The right light enhances and improves a space; bad lighting degrades it. Light has the power to transform the social context, creating zones of safety and comfort, making spaces more visible, more agreeable, more habitable and stimulating social interactions. In short, light is fundamental to the quality of life. Experiencing Light 2009 was the first international conference that had as its sole focus the effects of light and lighting design on human well-being. It approached well-being in its broadest sense, including mood, emotions, subjective and objective health, comfort, atmosphere perception, productivity and performance. The conference received inputs from perception research, environmental psychology, human factors, architecture, lighting design and industrial design. In this special issue we have selected some of its higher quality papers that reflect the breadth and wealth of this domain. The paper by Miller and colleagues presents recent insights in how nurses’ light exposure may be related to circadian disruption and – via this route – to human well-being; Schielke investigates how light – in particular luminaires – can assist organisations in communicating their corporate identity. The paper by Caberletti and colleagues describes the effects of interior lighting in cars on drivers’ perception inside the car and outside; Knight studied street lighting’s effects on perceptions of safety at night; Custers and colleagues determine lighting’s contribution to atmosphere perception in real-world retail settings; lastly, the paper by de Kort and Smolders describes a field test of effects of a dynamic lighting scenario on alertness and well-being of office workers. The papers published in this special issue showcase new research and findings on the psychological impact of light and as such represent a complementary perspective to more technology or design-oriented approaches, and one that is timely and relevant in furthering our understanding of the effects of light and lighting.