Attention deficit hyperactivity disorder BLT Bright light therapy CCT Correlated colour temperature CIE Commission Internationale de l'Eclairage CRSWD Circadian rhythm sleep-wake disorders DLMO Dim-light melatonin onset EEG Electroencephalogram GHT Geniculohypothalamic tract IGL Intergeniculate leaflet ipRGC Intrinsically photosensitive retinal ganglion cell LED Light-emitting diode PRC Phase response curve RGC Retinal ganglion cell RHT Retinohypothalamic tract RN Raphe nuclei SAD Seasonal affective disorder SCN Suprachiasmatic nuclei SSRI Selective serotonin reuptake inhibitor SWA Slow wave activity UV Ultraviolet Somnologie 3 • 2019 147

No abstract

LED *Shared senior authors. light sources have a discontinuous light spectrum with a prominent ‘blue’ peak between 450 and 470 nm that influences non-image forming responses in humans. We tested an LED lighting solution mimicking a daylight spectrum on visual comfort, circadian physiology, daytime alertness, mood, cognitive performance and sleep. Fifteen young males twice spent 49 hours in the laboratory under a conventional-LED and under a daylight-LED condition in a balanced cross over design flanked by a baseline and a post-light exposure night. Despite different light spectra, the photopic lux and the correlated colour temperature of the lighting were the same for both LEDs. The colour rendering index and the melanopic strength were 25.3% and 21%, respectively, higher for the daylight LED than the conventional LED. The volunteers had better visual comfort, felt more alert and happier in the morning and evening under daylight LED than conventional LED, while the diurnal melatonin profile, psychomotor vigilance and working memory performance were not significantly different. Delta EEG activity (0.75–4.5 Hz) was significantly higher after daylight-LED than conventional-LED exposure during the post-light exposure night. We have evidence that a daylight-LED solution has beneficial effects on visual comfort, daytime alertness, mood and sleep intensity in healthy volunteers.

Background Interest in biological clock pathways in bipolar disorders (BD) continues to grow, but there has yet to be an audit of circadian measurement tools for use in BD research and practice. Procedure The International Society for Bipolar Disorders Chronobiology Task Force conducted a critical integrative review of circadian methods that have real‐world applicability. Consensus discussion led to the selection of three domains to review—melatonin assessment, actigraphy, and self‐report. Results Measurement approaches used to quantify circadian function in BD are described in sufficient detail for researchers and clinicians to make pragmatic decisions about their use. A novel integration of the measurement literature is offered in the form of a provisional taxonomy distinguishing between circadian measures (the instruments and methods used to quantify circadian function, such as dim light melatonin onset) and circadian constructs (the biobehavioral processes to be measured, such as circadian phase). Conclusions Circadian variables are an important target of measurement in clinical practice and biomarker research. To improve reproducibility and clinical application of circadian constructs, an informed systematic approach to measurement is required. We trust that this review will decrease ambiguity in the literature and support theory‐based consideration of measurement options.