This is a randomized placebo-controlled trial to examine the efficacy of six-week bright light therapy as adjunctive treatment for patient with bipolar depression and eveningness.

This randomized placebo-controlled trial aims to evaluate the efficacy of adjunctive BLT in addition to their maintenance treatment in reducing depressive symptoms. The second aim of the study is to explore the effects of BLT on sleep-wake changes and the sleep disturbances.

Method: Each eligible participant will be randomized to either i) bright light therapy (BLT) or ii) inactive negative ion generator (placebo) treatment for 30-minutes daily at the midday for a total of six weeks. Participants will be evaluated at baseline, 2nd, 4th and 6th week for depression and insomnia symptoms. Actigraphy will be done at baseline and in the last week of treatment.

Inclusion Criteria:

1. Aged 18-65 years.
2. Is capable to give informed consent.
3. Meeting the diagnostic criteria of bipolar depression (including both bipolar I and II disorders) by the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-V), Disorders (SCID-V).
4. a score 20 or above representing current moderate or severe episode of major depression and a score of at least 1 on items H1 or H2 on the Structured Interview Guide for the Hamilton Depression Rating Scale with Atypical Depression Supplement (SIGH-ADS), corresponding to at least moderate severity.
5. A score of 41 or less by the Morningness-Eveningness Questionnaire which represents eveningness.
6. On a stable dose of antimanic treatment for bipolar disorder for at least four weeks.

Exclusion Criteria:

1. Major Depressive Disorder fulfilling the Seasonal Pattern Specifier of the DSM-V (Seasonal Affective Disorder).
2. A past history of rapid-cycling within the past twelve months or a Young Mania Rating Scale more than 12 at screening
3. A current or past history of schizophrenia, mental retardation, organic mental disorder; or current substance use disorder.
4. Presence of psychotic symptoms or substantial suicidal risk as judged by the clinician and/or screening instruments.
5. Presence of contraindications to bright light therapy: for example, history of light induced migraine/ epilepsy; current use of photosensitizing medications such as St. John's wart; presence of eye disease: e.g. retinal blindness, severe cataract, glaucoma, and photosensitive skin condition e.g. systemic lupus erythematosus
6. Significant medical condition/ hearing impairment/ speech deficit leading to incapability of completing clinical interview.
7. Regular shift-workers or trans-meridian flight in the past 3 months or during study
8. Enrolment in another clinical trial of an investigational medicinal product or device.
9. Receiving regular psychotherapy.

The subjects will be explained that the study aims to test the efficacy of the different modalities of non-pharmacological treatments for depression including bright light therapy and the negative ion generator, without mentioning which one is the placebo. An independent outcome assessor will be blinded to the treatment allocation throughout the study.