The study would enroll depressed adolescents and adults with bipolar I or II disorder or major depressive disorder who are receiving stable psychiatric medication (excluding patients with hypomania or mania, mixed symptoms, or rapid cycling). Participants would be randomly assigned to treatment with either 1,0000-lux bright white light therapy in the morning or 1,0000-lux bright white light therapy in the afternoon, or <100-lux dim red placebo light therapy in the afternoon (N=59 for each group). Participants would be treated for 6 weeks. Symptoms would be assessed every two weeks with the 24-items Hamilton Depression Scale, the Young Mania Rating Scale, and the Pittsburgh Sleep Quality Index; salivary melatonin and cortisol concentrations will be also measured.

The investigators would divide the participants enrolled into three groups: adjunctive morning bright light therapy (BLT) group (light intensity: 10000lux, color: white light, duration of each intervention session: 30min, time period of intervention: 7:00~9:00 a.m.), adjunctive afternoon BLT group (light intensity: 10000lux, color: white light, duration of each intervention session: 30min, time period of intervention: 12:00~14:00 p.m.), adjunctive placebo therapy group (light intensity: <100lux, color: dark red, duration of each intervention session: 30min, time period of intervention: 12:00~14:00 p.m.).

Inclusion Criteria:

• 12-75 years old
• Diagnosed using DSM-5 criteria based on the Structured Clinical Interview for Patient Edition (SCID-P) for adults or Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime version (Kiddie-SADS-PL) for adolescents for the diagnosis of bipolar I or II disorder or major depressive disorder
• 24-items Hamilton Depression Rating Scale score ≥ 20, Young Mania Rating Scale score < 6
• Participants with bipolar disorder taking at least one mood stabilizer, and the types of drugs have not changed in one week;
• Antidepressants can be taken, and the types of antidepressants have not changed in one week
• Low-dose benzodiazepines can be used, with a maximum of 2 mg of lorazepam equivalent per day
• Right-handed
• Primary school education or above
• Sign informed consents after a full explanation of this study.

Exclusion Criteria:

• A history of brain organic disease or severe traumatic brain injury and severe physical disease;
• Drug, alcohol or other psychoactive substance abusers
• Severe suicide risk;
• Received modified electric convulsion therapy (MECT) in the past three months
• Comorbid with ophthalmic diseases (cataract, macular degeneration, glaucoma, retinitis pigmentosa, etc.) and diseases affecting the retina (retinopathy, diabetes, herpes, etc.)
• Taking photosensitive drugs (phenothiazines, antimalarials, propranolol, melatonin, hypericum, stimulants or NSAIDs)