---
title: "Evidence: bright light entrains circadian rhythm"
description: "Bright light therapy effectively reduces depression symptoms and increases treatment response rates in adults with seasonal affective disorder."
url: "https://magellanlongevity.com/study/s194.md"
canonical: "https://magellanlongevity.com/study/s194.html"
html: "https://magellanlongevity.com/study/s194.html"
type: "study"
study_key: "s194"
journal: "Psychother Psychosom"
year: 2019
pmid: "31574513"
doi: "10.1159/000502891"
citations: 1
updated: 2026-09-02
author: "Gabriel Radu, DO"
author_credentials: "Physiatrist (PM&R). NY medical license 275110. NPI 1376861765."
publisher: "Magellan Longevity"
content_format: "markdown"
---

# Evidence: bright light entrains circadian rhythm

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**HTML version:** https://magellanlongevity.com/study/s194.html · **In the Magellan app:** https://magellanlongevity.com/#/study/s194

## Citation

| Field | Value |
| --- | --- |
| Journal | Psychother Psychosom |
| Year | 2019 |
| PMID | [31574513](https://pubmed.ncbi.nlm.nih.gov/31574513/) |
| DOI | [10.1159/000502891](https://doi.org/10.1159/000502891) |
| Study key | s194 |

## Takeaway

Bright light therapy effectively reduces depression symptoms and increases treatment response rates in adults with seasonal affective disorder.

## The question

Is bright light therapy (BLT) effective in treating seasonal affective disorder (SAD) in adults?

## Hypothesis

The study implicitly hypothesizes that bright light therapy (BLT) will be superior to placebo (dim light or sham/low-density negative ion generators) in treating seasonal affective disorder (SAD).

## Methods

This meta-analysis systematically searched for randomized, single- or double-blind clinical trials comparing BLT (≥1,000 lx) against dim light (≤400 lx) or sham/low-density negative ion generators. Primary outcome was post-treatment depression score, and secondary was treatment response rate. Only first-period data from crossover trials were used.

## Results

Nineteen studies were included. BLT was superior to placebo for depression ratings with a standardized mean difference of -0.37 (95% CI: -0.63 to -0.12) across 18 studies (610 patients). For response to active treatment, BLT had a risk ratio of 1.42 (95% CI: 1.08-1.85) across 16 studies (559 patients). No publication bias was found, but moderate heterogeneity and a moderate-to-high risk of bias were noted.

## Conclusion

Bright light therapy (BLT) is an effective treatment for seasonal affective disorder (SAD).

## Limitations

The available evidence comes from methodologically heterogeneous studies with small-to-medium sample sizes, and there was a moderate-to-high risk of bias.

## Verbatim from the abstract

> bright light therapy can be regarded as an effective treatment for seasonal affective disorder

## Where this study is used on Magellan

This paper is one of the citations behind the evidence grade on the pages below. Grades are assigned from the published research and are independent of affiliate commissions.

| Compound or device | Evidence grade | Graded pages |
| --- | --- | --- |
| Bright Light Therapy Lamp | Strong evidence | [Bright Light Therapy Lamp](https://magellanlongevity.com/p/194.md) |

## Reference

1. **Evidence: bright light entrains circadian rhythm**
   Psychother Psychosom 2019 · [PMID 31574513](https://pubmed.ncbi.nlm.nih.gov/31574513/) · [DOI 10.1159/000502891](https://doi.org/10.1159/000502891)

   > bright light therapy can be regarded as an effective treatment for seasonal affective disorder

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## Related on Magellan Longevity

- [Bright Light Therapy Lamp](https://magellanlongevity.com/p/194.md) — product graded on this and related evidence
- [Blue-Light Therapy for Seasonal and Non-Seasonal Depression: A Systematic Review and…](https://magellanlongevity.com/study/d35522196.md)
- [Efficacy of light therapy versus antidepressant drugs in major depressive episodes: a…](https://magellanlongevity.com/study/d31600678.md)
- [Longevity research map](https://magellanlongevity.com/longevity-research-map.html)
- [Evidence-based longevity supplements](https://magellanlongevity.com/longevity-supplements.md)

## Scope and disclosures

Educational information, not medical advice. Nothing here is intended to diagnose, treat, cure, or prevent any disease. Talk to your physician before starting any supplement or device, especially if you are pregnant, nursing, or taking medication.

Editorial firewall: evidence grades are assigned from the published research and are independent of any affiliate commission. As an Amazon Associate, Magellan Longevity earns from qualifying purchases.

Reviewed for accuracy by a board-certified physician (DO).