Lights On or Off? The Efficacy of Light Therapy as Add‐On to Cognitive Behavioural Therapy for Insomnia—A Pilot Study

Cognitive behavioural therapy for insomnia (CBT-I) is recommended as first-line treatment for insomnia disorder. However, around 25% of the patients do not respond to the treatment, and only 40% achieve full remission. The current study investigates the therapeutic potential of light therapy as an add-on to CBT-I. Insomnia severity and questionnaire-related secondary outcomes were assessed at baseline, post-treatment and follow-up. Sleep diary-related variables and the cortisol awakening response were assessed at pre- and post-treatment. Linear mixed models were calculated for each outcome variable. The study included 42 patients with insomnia disorder. Reduction in insomnia severity did not significantly differ between groups from baseline to post-treatment (β = 0.35, SE = 1.31, p = 0.792). Regarding exploratory secondary outcomes, daytime sleepiness was significantly more reduced from baseline to follow-up in the CBT-I + light therapy group than in the CBT-I + placebo light group (β = -1.05, SE = 0.43, p = 0.020). There was no significant condition × time point interaction effect for any of the other secondary outcomes. The findings show no significant add-on effect of light therapy on insomnia severity. However, light therapy had a significant effect on daytime sleepiness that became evident only at the follow-up. Given that daytime functioning is of high clinical relevance for patients with insomnia disorder, daytime sleepiness should be further evaluated as treatment target and may be addressed with light therapy. TRIAL REGISTRATION: ClinicalTrials.gov identifier: DRKS00029640.