All light is not equal: blue wavelengths are the most potent portion of the visible electromagnetic spectrum for circadian regulation. Therefore, blocking blue light could create a form of physiologic darkness. Because the timing and quantity of light and darkness both affect sleep, evening use of amber lenses to block blue light might affect sleep quality. Mood is also affected by light and sleep; therefore, mood might be affected by blue light blockade.
In this study, 20 adult volunteers were randomized to wear either blue-blocking (amber) or yellow-tinted (blocking ultraviolet only) safety glasses for 3 h prior to sleep.
Participants completed sleep diaries during a one-week baseline assessment and two weeks’ use of glasses.
Outcome measures were subjective: change in overall sleep quality and positive/negative affect. Results demonstrated that sleep quality at study outset was poorer in the amber lens than the control group. Two- by three-way ANOVA revealed significant (p < .001) interaction between quality of sleep over the three weeks and experimental condition.
- At the end of the study, the amber lens group experienced significant (p < .001) improvement in sleep quality relative to the control group and positive affect (p = .005).
- Mood also improved significantly relative to controls.
A replication with more detailed data on the subjects’ circadian baseline and objective outcome measures is warranted.