The benefits of bright light therapy for sleep have been known since the 1980’s. What is the current knowledge? The situation is quite complex because the effect of bright light therapy varies for different sleep disorders. Nevertheless, the Dutch meta-analysis from 2016 provides an optimal overview to begin with.
Results of the study
The authors collected 53 different studies published before 2015 investigating the effects of bright light therapy on sleep problems as the primary complaint. Therefore, they did not consider sleep problems related to depression or any other medical condition. There was one exception, though: studies on sleep problems in dementia were included, provided that the patients were living at home (thus being healthy enough to take care of themselves).
“Light therapy is effective in treating sleep problems.”van Maanen, Meijer, van der Heijden, Oort (2016). The effects of light therapy on sleep problems: A systematic review and meta-analysis. Sleep Medicine Reviews 29, 52-62.
How significant were the effects?
For insomnia symptoms, the effect was moderate-to–large. Insomnia symptoms cover a wide range of issues related to problems falling asleep, chronically waking up at night, and subsequent feelings of tiredness during the day. In terms of “effect size” the average effect was g=0.73, which is a surprisingly high number. Such an effect would be comparable to various behavioural and relaxation techniques and larger than self-help books or advice.
For circadian problems (meaning the sleeping phase not being synchronized with night as we would wish), the effect was moderate (g=0.63).
For sleep onset latency, the time spent in bed before finally falling asleep, the proven effect was rather small. Such latency is, however, generally difficult to influence, so even the effect of g=0.42 is reasonable. Unfortunately, we cannot see the result in terms of “minutes of nervous waiting before falling asleep” from the meta-analysis.
A small but still relevant effect was also found on daily fatigue (g=0.47) and sleepiness (g=0.41).
A minimal but relevant improvement was also found in sleep efficiency and total time of sleep.
Further, minimal effects, which are surely beneficial but too small to be clinically relevant, were found on optimization of sleep timing. Those who go to bed later fall asleep a bit faster and those who go to bed earlier sleep a bit longer.
What does this mean practically?
Imagine an average patient with insomnia, who has more severe symptoms than half of the others and less severe than the other half (that is why he is the average one, after all). If he receives bright light therapy, he would be better off than three quarters of the others. Of course, that does not make light the ultimate cure, but it indicates a notable improvement.
Plus, the effect was even higher when more intensive light was used. On the other hand, these results are likely to be overestimated by the design of the studies. Therefore, the real effect is probably a bit less surprising – but surely still large enough to be considered helpful.
These effects are not precise, being underestimated and exaggerated at the same time.
- First, they are averaging together multiple studies with different lamps and design. This impairs the results as they are influenced by studies with lower intensity light or improper light timing compared to today’s standards. Some of the studies included are even from the 1980’s!
- Second, if you discover a significant effect, scientific journals are more likely to publish your results. This makes the effect look stronger because there may be other, less successful studies which didn’t get their results published and thus are not included in the meta-analysis.
For practical purposes, we may consider these two confounding factors to cancel each other out. However, it is important to know that various sleep problems differ. Take a look on different causes of sleeplessness before making any decision!
The effects of bright light therapy on most sleep problems are proven and clinically significant, especially in insomnia. Provided you use a strong enough light and are sticking to the treatment plan, you can benefit more than the average patient from the studies.