ISBD Issues First Clinical Guidelines for Light Therapy in Bipolar Disorder

Bipolar disorder imposes a disproportionate burden of depressive episodes, yet first-line treatments remain limited in efficacy and accessibility. Bright light therapy (BLT) has accumulated a growing evidence base but remains underutilized in psychiatric practice. To address this gap, the ISBD Chronobiology and Chronotherapy Task Force—comprising 23 international experts in psychiatry, chronobiology, and sleep medicine—conducted a comprehensive evidence review and formulated clinical practice recommendations published in Dialogues in Clinical Neuroscience (2025).

The review situates BLT within the neurobiology of the circadian system. The suprachiasmatic nucleus (SCN), the brain's master clock (~20,000 neurons), receives photic input via intrinsically photosensitive retinal ganglion cells (ipRGCs) expressing melanopsin, maximally sensitive to blue light (~480 nm). Disruption of this system—common in BD—manifests as delayed or advanced sleep phase, irregular sleep-wake cycles, and seasonal mood variation. BLT acts directly on this pathway, resetting circadian timing and normalizing downstream monoaminergic and hormonal rhythms implicated in mood regulation.

The task force reviewed randomized controlled trials and systematic evidence on BLT in bipolar depression, finding higher-quality support for adjunctive BLT as an acute antidepressant intervention. Effective protocols use 10,000-lux white light delivered for 30 minutes per day, ideally in the morning or at midday. Midday exposure is an acceptable alternative for patients unable to tolerate early morning sessions, avoiding the circadian disruption of excessively early wake times. For patients concerned about hypomanic switching or partial responders, a gradual titration starting at 15 minutes/day with weekly 15-minute increases to 30–60 minutes/day by week four is recommended.

A critical safety consideration is the risk of manic or hypomanic switch, particularly in BD-I. The guidelines strongly recommend concurrent anti-manic pharmacotherapy (mood stabilizer coverage) before initiating BLT, along with regular clinical monitoring throughout treatment. Clinical improvement is typically observable within 1–2 weeks; full response or remission is expected by 4–6 weeks. Integration with other chronotherapeutic strategies—such as sleep deprivation/wake therapy, melatonin, and interpersonal social rhythm therapy—may further enhance long-term outcomes. Evidence for maintenance BLT as a relapse-prevention strategy remains insufficient and warrants dedicated investigation.

The guidelines acknowledge that most trials are small and conducted in heterogeneous populations, and that optimal personalization of timing (based on chronotype and circadian phase assessment) requires further study. Nonetheless, BLT represents a low-cost, low-risk, and mechanistically grounded adjunctive intervention that clinicians can implement with appropriate safeguards.