In this study, we will utilize the optocoupler-controllable light source, a product jointly developed by the School of Physics at Peking University and Peking University Sixth Hospital, which granted a national patent in China, for the purpose of intervention. Participants randomly assigned to the low light density intervention group will receive bright white light therapy interventions with light intensities of 5,000 lux,and the main wavelength of light source is 476.4nm. The intervention plan is to receive 40 minutes of light therapy from 6:30-10:00 in the morning for 4 consecutive weeks, 6 days a week. The subject sits at a distance of 60cm from the light source.

In this study, participants randomly assigned to the placebo-controlled group will receive dim red light therapy interventions with light intensities of 100 lux, and the main wavelength of light source is 690.4nm. The placebo-controlled intervention plan is to receive 40 minutes of red light therapy from 6:30-10:00 in the morning for 4 consecutive weeks, 6 days a week. The subject sits at a distance of 60cm from the light source.

The QIDS-SR, first developed and validated by Rush and colleagues in 2003, is a DSM-IV-based self-report tool specifically designed to assess depressive symptomatology over a seven-day recall period42. The QIDS-SR16 has been validated as a reliable and effective instrument for adolescent outpatients, demonstrating high internal consistency and a robust unidimensional structure. It comprises 16 items, each rated on a 0-3 point scale, with higher total scores indicating greater severity of depressive symptoms. In this study, the QIDS-SR was used to assess self-reported depressive symptoms.

The PSQI, developed by Buysse et al. in 1989 at the University of Pittsburgh, is a self-rated questionnaire designed to assess sleep quality. The Chinese version of the PSQI, validated by Liu et al., demonstrated high internal consistency with a Cronbach's alpha of 0.84 and excellent test-retest reliability with an r value of 0.81 over a two-week period. It comprises nine items: the first four are open-ended, and the remaining five are multiple-choice, with Item 5 containing ten sub-items. These items collectively evaluate seven sleep components, each scored 0-3, yielding a global score ranging from 0 to 21, with higher scores indicating poorer sleep quality.

HVLT-R is a widely used neuropsychological assessment tool designed to evaluate verbal memory and cognitive function. Developed by J. Brandt and Benedict in 2001, the HVLT-R consists of a list of 12 nouns divided into three semantic categories (e.g., dwelling places, four-legged animals, and precious stones), with four words per category. The assessment involves three learning trials, where participants are presented with the list of words and are asked to recall as many words as possible immediately after each presentation. Additionally, there is a delayed recall trial, where participants are asked to recall the words after a delay of 20-25 minutes. The scoring principle is based on the number of correctly recalled words during each learning trial and the delayed recall trial. The total scores of the three learning trials and the delayed recall trial were computed to represent verbal learning and memory function.

Brief Visuospatial Memory Test-Revised is a neuropsychological assessment tool designed to evaluate visual spatial memory. Developed by researchers including Barr, Morrison, Zaroff, and Devinsky in 2004, the BVMT-R consists of six geometric figures presented in a 2x3 array, serving as the stimuli for the test. The assessment involves three learning trials, where participants are shown the stimuli for 10 seconds and are then asked to draw as many of the figures as possible in the correct locations on a response sheet. After a delay of approximately 25 minutes, a delayed recall trial is administered, followed by a recognition trial where participants are asked to identify the original geometric figures among a set of 12. The scoring principle is based on the number of correctly recalled and recognized figures, reflecting participants' visuospatial memory ability.

The Color Trails Test (CTT) is a neuropsychological assessment tool specifically designed to minimize cultural and linguistic biases by using colors instead of letters. The test consists of two parts: CTT-1 and CTT-2, each preceded by a brief practice session.

1. CTT-1: The examinee is required to connect circles numbered 1 through 25 in ascending order as quickly as possible. In this part, all circles are of a uniform color (typically yellow or pink). This part primarily assesses the examinee's psychomotor speed and visual scanning abilities.
2. CTT-2: This part consists of 50 circles, containing two sets of numbers from 1 to 25. Each number appears twice: once in a pink circle and once in a yellow circle. The examinee must connect the numbers in ascending order (1-2-3...) while simultaneously alternating between the two colors (e.g., 1-Pink, 2-Yellow, 3-Pink, 4-Yellow...). This part serves as a sensitive measure of sustained attention, divided attention, and cognitive flexibility.

The GSES, based on Bandura's self-efficacy theory, originally developed by Schwarzer and Jerusalem in 1981, and revised for the Chinese population by Wang et al., evaluates an individual's perceived ability to cope with setbacks or challenges. It comprises 10 items rated on a 4-point Likert scale (1-4), with total scores ranging from 10 to 40; higher scores indicate greater self-efficacy.

Developed by Young et al. in 1978, the YMRS is a widely utilized clinician-administered tool designed to quantify the severity of manic symptoms. It comprises 11 items evaluating domains such as mood elevation, increased motor activity, irritability, speech, thought content, and sleep disturbance. Four items (irritability, speech, thought content, and disruptive/aggressive behavior) are graded on a 0 to 8 Likert scale to capture a broader range of severity, while the remaining seven items are graded on a 0 to 4 scale. Total scores range from 0 to 60, with higher scores indicating greater manic severity.

Originally introduced by Åsberg et al. in 1978, the Side Effects Rating Scale (SERS) is a standardized instrument employed to assess the burden of common antidepressant-induced adverse events. Each SERS item is rated on a 0-3-point scale with the following criteria: (0) absent; (1) mild; (2) moderate; (3) severe. Outcome measures include individual item scores and total scores, with higher scores indicating greater side effect severity. This study utilized the SERS to assess both the alleviation of somatic symptoms and the potential adverse effects associated with the light therapy intervention.

Developed by Stringaris et al. in 2012 to measure irritability in youths, the ARI evaluates the threshold, frequency, and duration of irritable manifestations. The 7-item scale is rated from 0 (not true) to 2 (certainly true). The total score is the sum of the first six items, while the seventh item independently assesses impairment. The Chinese adaptation of the ARI has demonstrated good convergent and concurrent validity, alongside robust reliability among adolescents.

The SCWT was developed by Professor Stroop in 1935 to evaluate subjects' executive functions. The test is a measure of selective attention and the degree of inhibition of irrelevant information in executive functioning. It consists of three main parts: reading words (Stroop-w), color naming (Stroop-c), and color-word interference (Stroop-cw), which require subjects to accurately and quickly read the words or the colors, respectively, as required.

Developed by Nixon and Cloutier in the late 1990s, the OSI comprehensively assesses non-suicidal self-injury (NSSI) behaviors and addictive features. The Chinese OSI demonstrated favorable reliability and validity in adolescent cohorts. NSSI frequency over the past month is scored on a 4-point scale, whereas longer-term frequencies (e.g., past 6 months, past year) use a 5-point scale. In this study, the OSI items were employed to evaluate NSSI/suicide attempt frequency, severity, history, onset age, emotional triggers, and disclosure.

Response will be defined as a ≥50% reduction in the total score of the HAMD-17 from baseline.

Remission will be defined as achieving a HAMD-17 score of ≤7 points at T4.

Originally developed by Hamilton in 195944, the HAMA is a classic clinician-administered questionnaire assessing both somatic and psychic anxiety severity. The 14-item instrument captures psychic anxiety (items 1-6, 14) and somatic anxiety (items 7-13). Each item is rated on a 5-point Likert scale from 0 (absent) to 4 (very severe), with higher total scores indicating more severe clinical anxiety. The construct validity and reliability of the Chinese HAMA adaptation have been rigorously established in domestic psychometric studies.In this study, the HAMA was used to assess the severity of anxiety symptoms.

The sleep diary used in this study was adapted from the National Sleep Foundation Sleep Diary (MSFSD) and consists of two sections: morning and evening entries. Morning entries assess bedtime, wake-up time, sleep latency, number of nocturnal awakenings, subjective morning alertness, total sleep duration, and factors disrupting sleep. Evening entries assess daytime nap frequency and duration, physical activity and outdoor exposure, caffeine intake, pre-sleep dietary intake and hydration, electronic device usage before bedtime, and activities during the hour preceding sleep.

Each interview will last around 30 minutes and will be conducted via secure videoconferencing platforms. The interview guide will explore participants' experiences with home-based BLT, including perceived impacts on daily life, expectations of treatment efficacy, attitudes toward home-based delivery, and willingness to recommend BLT to adolescents with similar needs.Semi-structured interviews were used to assess the applicability of BLT.

During the resting-state recording, subjects will be instructed to keep their eyes open, remain awake, maintain a relaxed state, and refrain from engaging in thoughts that could influence their mood. In each run, eight minutes of resting-state fNIRS data are acquired. The experimental task was based on a standardized Chinese VFT paradigm and comprised three phases: a 30-second baseline rest, a 60-second active word-generation period, and a 70-second recovery phase53. During the rest phases, participants were instructed to fixate on a central point while counting aloud from 1 to 5. During the task, participants are instructed to generate compound words using the Chinese characters '白' (white), '天' (sky), and '大' (big), which are presented sequentially. Resting-state functional connectivity and task-related cortical activation levels were extracted as outcome measures.

The CPT-IP was administered using the CBCT software. Participants were instructed to press the response key as quickly as possible when specific "target stimuli"-i.e., animal pictures-appeared on the screen.

When distractor stimuli were presented, participants were required to withhold their keypress response. This test is primarily used to assess participants' sustained attention, vigilance, and impulse control.

The Trail Making Test Part A (TMT-A) requires the examinee to connect 25 randomly distributed circles in ascending numerical order (1-2-3...) as quickly as possible without lifting the pen, serving as a standardized measure of visual scanning, psychomotor speed, and motor coordination.