A new light source (Valkee©) does not alter sleep–wake parameters and does not improve mood in phase delayed subjects


Not much evidence exists concerning the effects on sleep and mood of transcranial bright light. In this study, 50 students, all with wake-up time 9:00 a.m. or later in weekends/free days, participated in a double-blind placebo-controlled experiment comparing the effects of bright light (n = 27; 8.0 lm) and placebo (n = 23; 0.1 lm). Data collection consisted of sleep assessment, with both sleep diaries and actigraphy. In addition, the Fatigue Severity Scale and the Profile of Mood States (POMS) were administered. Following 1 week of baseline recording, the therapy was initiated, aiming to phase advance the sleep–wake period. The therapy lasted for 2 weeks and consisted of gradually advancing daily light exposure of 12 min’ transcranial bright light. Subjects in the two conditions did not change differently from baseline to post-treatment on any sleep parameters. A significant condition × time interaction was found for one of six subscales (vigor–activity) of the POMS, suggesting a more favorable development from baseline to post-treatment in the placebo compared to the bright light condition. No differences in terms of side-effects were reported between conditions. It is concluded that transcranial bright light, at times where conventional light therapy has phase-advancing properties, did not influence any sleep parameters differently than placebo. Transcranial bright light was associated with a less favorable development from baseline to post-treatment on one mood parameter compared to placebo.

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The authors received 12,000 Euros from Valkee® covering expenses related to the conduct of the present study.

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Correspondence to Ståle Pallesen.

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Pallesen, S., Nødtvedt, Ø., Saxvig, I.W. et al. A new light source (Valkee©) does not alter sleep–wake parameters and does not improve mood in phase delayed subjects. Sleep Biol. Rhythms 14, 97–105 (2016). https://doi.org/10.1007/s41105-015-0027-5

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  • Transcranial bright light
  • Sleep–wake rhythm
  • Mood
  • Randomized controlled trial