This outpatient study was performed at Ann \& Robert H. Lurie Children's Hospital of Chicago. The Institutional Review Boards (IRB) of Lurie Children's Hospital and Northwestern University, Feinberg School of Medicine approved the protocol. Participants were recruited through partnering community pediatric practices (namely Lake Forest Pediatrics). Primary care pediatricians referred potential participants with depression and elevated scores on youth screening measures, Patient Health Questionnaire-9 (≥ 9) or PHQ-2 (≥ 3), without endorsed suicidality.

Light Therapy Protocol with Placebo Lead-in. Eligible participants were provided a light box and an actigraphy wrist watch and given instructions on the use of each. The active light box (Carex DayLight Classic Model) is a white fluorescent 4000 Kelvin unit that emits 10,000 lux and measures 33cm x 40cm. The placebo box emits 50 lux dim red light and appears identical to the active unit. Dim red light was selected because the illumination is a plausible placebo in clinical trials of BLT for depressive disorders and produces negligible effects on circadian rhythms and mood responses. Subjects were instructed to position themselves 30-36 cm from the box with their faces fully exposed to the light. The actigraphy device is a Philips Spectrum Plus actigraphy watch which collects activity level and sleep information along with multiple light measurements and wearer adherence. The light therapy dosing protocol was planned as follows: Weeks 0-2, 50 lux dim red light (DRL) x 30 minutes/day; weeks 3-4, 10,000 lux x 15 minutes/day; weeks 5-6, 10,000 lux x 30 minutes/day; weeks 6-8, 10,000 lux x 45 minutes/day. At week 2, the study coordinator (KJ) dispensed the 10,000 lux BLT unit (and picked up the dim red light box) and the actigraph watch. Participants and their parent/guardian met with 2 study clinicians at the end of each 2-week period. One study clinician (RB or JP), who was blinded to the participant's light box use, conducted a brief interview regarding mood, safety and functioning, and assigned a Clinical Global Impressions Scale-Severity (CGI-S). The other study clinician (DKS) subsequently met with the participant to review safety, side effects and response and made recommendations on duration and timing of light box use based on level of improvement and any barriers to use. Thus, some patients did not receive the above dosing schedule. After the 8-week active study period, participants who had symptom remission were given the option to keep the light box and continue use. A treatment summary and ongoing treatment recommendations were provided to all participant's primary care clinicians.

Adherence. The study coordinator made weekly calls/texts to participants to inquire about their daily exposure times and to encourage proper adherence. The constraints imposed upon adolescents by schools (early morning start times by 8:00 AM), bus commutes (pick up by 7:30 AM), after school activities and part-time jobs (landscaping etc.) are considerable. Knowing this and to avoid forcing adolescents to wake earlier than preferred (which can produce detrimental effects on adolescent sleep and mood) to use the study light box, participants agreed to initiate BLT exposure in the morning at awakening in accordance to the dosing protocol. At follow up visits, the non-blind clinician systematically explored whether morning use remained feasible and acceptable. If not, the clinician made informed clinical recommendations and recorded adjustments to the time-of-day of use (midday or afternoon) to ensure participants were able to consistently use the box. This strategy informed investigators and participants of the optimal timing of light exposure, increased adherence and strengthened the reliability of detecting response.

Actigraphic Assessments. Actigraphy using a wrist actigraph with a light sensor (Actiwatch Spectrum, Philips Respironics Healthcare, Bend, OR, USA) was used to measure a number of actigraphic-derived sleep, circadian, activity and light variables during the placebo and active light treatment phases.