Effectiveness of Light Therapy Across Seasons

May 18, 2026 updated by: Claudia Simons, Geestelijke Gezondheidszorg Eindhoven (GGzE)

Is the Antidepressant Effect of Light Therapy for People With a Depressive Disorder Comparable in the Spring/Summer vs Autumn/Winter?

This study investigates whether the antidepressant effects of bright light therapy (BLT) differ between the spring/summer season and the autumn/winter season in adults with depressive disorders. While BLT is an established treatment for seasonal affective disorder, increasing evidence suggests it may also be effective for non-seasonal depression. However, it remains unclear whether its effectiveness depends on seasonal variation in natural daylight exposure.

In this prospective study conducted in a routine clinical care setting, patients referred for depressive symptoms and a score of > 6 on the Quick Inventory of Depressive Symptomatology-Self-Report (QIDS-SR) receive BLT in a structured "Light Café" environment. Participants undergo daily morning light therapy sessions (30 minutes at 10,000 lux) for at least one week, with possible extension up to three weeks based on treatment response. A delayed-start design is used, where a subset of participants begins treatment two weeks later, allowing comparison with the natural course of depressive symptoms.

Depressive symptoms are assessed using the QIDS-SR at baseline, during treatment, and at follow-up (6 weeks and 3 months post-treatment). Sleep quality, chronotype, circadian timing, and side effects are also measured.

The primary objective is to compare the effectiveness of BLT across seasons. Secondary objectives include evaluating the persistence of treatment effects, assessing the change in sleep quality and day-to-day sleep-wake pattern, and exploring whether outcomes vary by chronotype, circadian phase, and patient characteristics.

This study aims to inform whether BLT should be considered a year-round treatment option for depressive disorders and to better understand factors influencing individual treatment response.

Study Overview

Status

Completed

Conditions

Intervention / Treatment

Study Type

Observational

Enrollment (Actual)

212

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

No

Sampling Method

Non-Probability Sample

Study Population

The study population consists of patients with depression who are referred for treatment of depressive symptoms within a mental health care setting (GGzE, Eindhoven, The Netherlands), where bright light therapy is offered in a structured "Light Café" environment as part of routine clinical care.

Description

Inclusion Criteria:

  • Adults aged 18 years or older
  • Diagnosis of a depressive disorder (unipolar or bipolar), including both seasonal and non-seasonal depression
  • Currently indicated for bright light therapy
  • QIDS-SR score ≥ 6 at baseline
  • Able to provide informed consent
  • Sufficient proficiency in Dutch or English to complete questionnaires

Exclusion Criteria:

  • Current (hypo)manic or mixed episode
  • Current psychotic episode
  • Severe suicidal ideation requiring immediate intervention
  • Diagnosis of dementia
  • QIDS-SR score ≤ 5 at baseline
  • Age < 18 years
  • Inability to provide informed consent
  • Insufficient language proficiency to complete study questionnaires
  • Initiation, dose change, or switch of antidepressant medication within 3 weeks before or during light therapy
  • Long-term use of agomelatine

Relative Contraindications (require consultation with treating physician before participation):

  • Pregnancy (first trimester)
  • Diabetes or other systemic vascular diseases
  • Eye conditions associated with increased light sensitivity
  • Epilepsy

Medication-Related Considerations:

  • Participants are advised not to start antibiotics during light therapy (existing courses should be completed prior to participation)
  • Participants are advised to discontinue use of photosensitizing medications or topical agents during treatment
  • Participants are asked to discontinue melatonin use during light therapy
  • A wash-out period of 1 month is required after discontinuation of melatonin or short-term agomelatine use before starting light therapy

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

Cohorts and Interventions

Group / Cohort
Intervention / Treatment
Spring/summer
Patients with a depression who received bright light therapy as part of routine clinical care. For the purpose of the analyses, participants were categorized based on the season of treatment initiation, with this cohort including those who started treatment during the spring and summer seasons.
Device: Bright Light Therapy
Bright Light Therapy (BLT) will be administered according to Dutch depression guidelines, using Innolux LED light lamp (3800K, 10,000 lux). BLT will be given for one work week (Mon-Fri), 7:30-10:30 AM, 30 mins/session. Patients can have breakfast, read, or use devices. Treatment effectiveness will be evaluated using Self-Rated Quick Inventory of Depressive Symptoms (QIDS-SR). If remission is achieved (QIDS-SR < 6), no additional treatment is given. If response is insufficient (QIDS-SR ≥ 6), 5 more sessions will be added in the following week, with maximum two extensions (1-3 weeks total).
Autumn/winter
Patients with a depression who received bright light therapy as part of routine clinical care. For the purpose of the analyses, participants were categorized based on the season of treatment initiation, with this cohort including those who started treatment during the autumn and winter seasons.
Device: Bright Light Therapy
Bright Light Therapy (BLT) will be administered according to Dutch depression guidelines, using Innolux LED light lamp (3800K, 10,000 lux). BLT will be given for one work week (Mon-Fri), 7:30-10:30 AM, 30 mins/session. Patients can have breakfast, read, or use devices. Treatment effectiveness will be evaluated using Self-Rated Quick Inventory of Depressive Symptoms (QIDS-SR). If remission is achieved (QIDS-SR < 6), no additional treatment is given. If response is insufficient (QIDS-SR ≥ 6), 5 more sessions will be added in the following week, with maximum two extensions (1-3 weeks total).

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Change in depressive symptom severity (QIDS-SR)
Time Frame: Baseline to end of treatment (approximately 1-3 weeks after initiation of light therapy)
Depressive symptom severity is assessed using the Quick Inventory of Depressive Symptomatology - Self-Report (QIDS-SR), a validated 16-item questionnaire with total scores ranging from 0 to 27 (higher scores indicating greater symptom severity). The primary outcome is the change in QIDS-SR score from baseline (pre-treatment) to end of light therapy. The analysis compares changes between participants treated in the spring/summer season and those treated in the autumn/winter season, while accounting for the delayed-start control condition.
Baseline to end of treatment (approximately 1-3 weeks after initiation of light therapy)

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Sustained change in depressive symptoms (QIDS-SR follow-up)
Time Frame: End of treatment to 6 weeks and 3 months post-treatment
Depressive symptom severity is assessed using the Quick Inventory of Depressive Symptomatology - Self-Report (QIDS-SR), a validated 16-item questionnaire with total scores ranging from 0 to 27 (higher scores indicating greater symptom severity). This secondary outcome evaluates the persistence of treatment effects by comparing post-treatment scores to follow-up scores.
End of treatment to 6 weeks and 3 months post-treatment
Change in sleep quality (PSQI)
Time Frame: Baseline to 6 weeks and 3 months post-treatment
Sleep quality is measured using the Pittsburgh Sleep Quality Index (PSQI), a validated self-report questionnaire with total scores ranging from 0 to 21 (higher scores indicating poorer sleep quality). The outcome reflects change in sleep quality following light therapy.
Baseline to 6 weeks and 3 months post-treatment
Chronotype (MEQ)
Time Frame: Baseline (chronotype assessment), end of treatment (1-3 weeks after initiation of light therapy), 6 weeks post-treatment, and 3 months post-treatment
Chronotype is assessed using the Morningness-Eveningness Questionnaire (MEQ). This outcome examines whether baseline chronotype moderates changes in depressive symptom severity following light therapy.
Baseline (chronotype assessment), end of treatment (1-3 weeks after initiation of light therapy), 6 weeks post-treatment, and 3 months post-treatment
Adverse Events and Side Effects
Time Frame: At the end of each treatment week, up to 3 weeks
Side effects are assessed using a self-report questionnaire capturing the presence and severity of common light therapy-related symptoms (e.g., headache, eye irritation, sleep disturbances).
At the end of each treatment week, up to 3 weeks
Change in Sleep-Wake Pattern during treatment
Time Frame: Twice weekly during treatment, up to 3 weeks
Sleep timing, duration, quality and fragmentation, are assessed using a shortened sleep diary based on the Consensus Sleep Diary. This outcome evaluates changes in sleep patterns during light therapy and their relation to treatment response. Participants completed the diaries in the clinic on Mondays and Fridays, reporting retrospectively on their sleep during the preceding nights (i.e., Friday-Sunday nights for Monday entries and Monday-Thursday nights for Friday entries).
Twice weekly during treatment, up to 3 weeks

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Geestelijke Gezondheidszorg Eindhoven (GGzE)

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

January 1, 2021

Primary Completion (Actual)

October 7, 2022

Study Completion (Actual)

December 23, 2022

Study Registration Dates

First Submitted

May 12, 2026

First Submitted That Met QC Criteria

May 18, 2026

First Posted (Actual)

May 20, 2026

Study Record Updates

Last Update Posted (Actual)

May 20, 2026

Last Update Submitted That Met QC Criteria

May 18, 2026

Last Verified

May 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • ILB/2020038

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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