Light Therapy for Insomnia: Here's How It Works

Light therapy is a potential insomnia treatment for circadian rhythm disorders.

Basically, if someone’s circadian rhythm gets out of sync due to a weird sleep schedule or not getting enough light, bright light therapy may be able to correct the schedule.

There’s a decent amount of research that shows that bright light therapy works in some cases but not others. The science isn’t fully settled here, but I’ll walk you through what’s currently known.

Does Light Therapy Work for Insomnia?

A 2016 systematic review and meta-analysis looked at 53 studies (1154 subjects) that looked at the effects of light therapy on sleep (1).

Overall, there was a significant positive effect of light therapy on sleep problems in general, including circadian rhythm sleep disorders and insomnia.

As you can see, some studies showed a large positive effect, but overall the effect size is typically small to medium.

One note by the authors of the review is that higher light intensities led to larger effect sizes.

Signs of Circadian Rhythm Disorders

It's fairly difficult to diagnose a circadian rhythm disorder, but there are some common signs.

People with this type of disorder are often very alert at night, and also sleep better during the day.

When is Bright Light Therapy Effective?

The fact that most studies have found some positive effect of light therapy is a good sign.

We still don’t know things like:

• What’s the optimal duration of light therapy?
• What light intensity is ideal?
• What’s the best timing for therapy?

As these things are figured out, results may get even better.

For now, we know that the populations that are most at risk of developing circadian rhythm disorders are:

• Night shift workers
• People with seasonal affective disorder (SAD)
• Elderly people with depression and insomnia

While the methodology for previous studies varies quite a bit, most studies expose subjects to bright light in the morning (or at the start of a night shift) (2).

For example, one study exposed nurses working the night shift to bright light during the first half of the shift before reducing it gradually until the end (3). The effect on insomnia severity index scores was quite large and statistically significant:

How Does Light Therapy Work?

The circadian rhythm is largely regulated by light exposure (sunlight in particular).

Sunlight in the morning suppresses melatonin production and kickstarts the entire cycle, which is the idea behind bright light therapy (4).

For night shift workers, using bright light therapy just before or at the start of the shift essentially sets that time as the “morning” in their bodies, which can improve sleep later on.

SummaryBright light therapy can only potentially have a positive effect on insomnia when the patient has some sort of circadian rhythm disorder. If the root cause is stress related (or some other cause), it’s unlikely for light therapy to have much, if any, effect.

Summary: Bright Light and Insomnia

Unlike treatment methods like cognitive behavioral therapy, light therapy is very situational.

Research suggests that light therapy can have a significant effect on insomnia symptoms in patients that have circadian rhythm disorders.

The optimal timing, frequency, and duration for bright light therapy is still under investigation. For now, it appears that a few hours first thing in the morning (or relative “morning” for night shift workers) is most effective.

References

1. The effects of light therapy on sleep problems: A systematic review and meta-analysis
2. Bright-light treatment reduces actigraphic-measured daytime sleep in nursing home patients with dementia
3. The Effectiveness of Light/Dark Exposure to Treat Insomnia in Female Nurses Undertaking Shift Work during the Evening/Night Shift
4. Light Therapy for Insomnia in Older Adults