German Clinical Trials Register

Acronym/abbreviation of the study

LIGHT.Sleep

URL of the study

No Entry

Brief summary in lay language

Electric light is one of the most important achievements of modern society. At the same time, the artificial illumination of the environment is also a great challenge for our organism. Blue light in particular plays a decisive role in this respect and it is now known that this also affects sleep. However, we know very little about how artificial light in the evening alters brain processes that underlie these negative effects. The aim of this research project is to find out. To do this, healthy volunteers will be exposed to two different light sources, one with a high and one with a low blue light component, on two days before going to bed. It will then be investigated how the two light sources affect sleep quality and how they change the interaction between the brain and environmental stimuli during waking, i.e. during light exposure, and in subsequent sleep, and whether differences are still present after waking the next morning. Specifically, we will investigate how light exposure affects the brain's ability to learn and thus predict the occurrence of environmental stimuli and how light alters the processing of relevant linguistic stimuli such as one's own first name compared to other first names or a very familiar voice (e.g. one's own parents) compared to an unknown voice. Comparison of the two lighting conditions will generate knowledge about how artificial light alters the interaction between the brain and environmental stimuli in waking and sleeping. We expect blue light to make the processing of stimuli more awake-like even during sleep, which could be the reason for the negative effects on sleep quality. Findings in this respect are highly relevant, for example, for recommendations on how to design the evening lighting environment for good sleep.

Brief summary in scientific language

It is well-known that artificial light exposure in the evening can increase alertness, decrease fatigue and alter sleep. That is particularly true for back-lit screens as used in e.g. smartphones or e-readers as they emit light with a peak in the blue light spectrum, which our circadian system is especially sensitive to. More precisely, intrinsically photosensitive retinal ganglion cells (ipRGCs) with peak sensitivity at wavelengths between 460 and 480nm, i.e. in the blue spectrum, relay information about the spectral composition of light to the biological clock in the suprachiasmatic nuclei of the hypothalamus, which regulates manifold processes according to the circadian phase. Little is however known about why and how exactly artificial light in the evening alters sleep. We, Dr Blume and Prof Cajochen, believe that two paradigms that have previously been used to study cognitive processing during wakefulness and sleep can be used to investigate this question. In particular, we will use a variant of the classic oddball paradigm that allows investigating predictive coding, a basic form of learning, on two levels of complexity. In a second paradigm we will investigate how more ecologically valid linguistic stimuli of varying subjective and emotional relevance (i.e. one’s own vs. unfamiliar names uttered by a highly familiar vs. unfamiliar voice) are processed. Crucially, to investigate the effects of artificial light on processing acutely during wakefulness as well as subsequent sleep, participants will undergo two light exposure conditions. In each of these, participants will be exposed to 40min of light in the evening. In one condition the light spectrum will be modulated such that it exhibits a spectral peak between 460 and 480nm (melanopic high) whereas in the other light proportions in this wavelength range will be decreased (melanopic low). We will use electroencephalography (EEG) to investigate differences in cognitive processing between the two light exposure conditions by means of event-related potentials and evoked oscillatory responses. Beyond this, we will also investigate previously proposed genetic differences in the sensitivity to blue light and how they interact with cognitive processing following light exposure. Evening profiles of salivary melatonin levels will serve as an additional control for the non-visual impact of the light conditions on circadian physiology. Ultimately, the knowledge gained in this research project will help to better understand how the use of light-emitting devices in the evening changes cognitive processing and sleep. It thus has a high relevance for understanding the specific effects artificial light as a major technological achievement has on a state critical for health and well-being. Eventually, this may inform about how to best design light environments in the evening, which may be especially relevant with regard to shift work, i.e. work in a light environment that is at odds with the time of day.