Blue and red light in the afternoon dip (Sahin 2013)
EEG markers of sleepiness (alpha, alpha-theta and theta power) were lower after light exposure, and the authors conclude that melatonin suppression is not needed for light to have an alerting effect.
The question: Does coloured light make people more alert in the daytime, when melatonin is already low?
| Type of study | Experiment |
|---|---|
| Who took part | Adults with regular sleep schedules (number not given in the abstract) |
| What was done | 48-minute exposures to blue (470 nm) or red (630 nm) light at 40 lux at the eye, near the post-lunch dip, with EEG. |
| How much weight it carries | Mixed evidence |
What it found
- Power in the alpha, alpha-theta and theta ranges was significantly lower after light exposure than in darkness.
- The result extends earlier night-time findings to the afternoon.
- The authors conclude that acute melatonin suppression is not needed for an alerting effect.
Limits
- 40 lux at the eye for 48 minutes is a controlled dose; a phone held at arm's length delivers less.
- EEG markers, not performance at work.
- Small laboratory study from one group.
Where this sits
More in the library on light, flicker and 40 hz. For the wider picture, read 40 Hz, gamma and the brain.
This is our plain-language reading of the paper. It is not medical advice, and one study rarely settles a question.
Sources
- Sahin, L., & Figueiro, M. G. (2013). Alerting effects of short-wavelength (blue) and long-wavelength (red) lights in the afternoon. Physiology & Behavior. doi.org/10.1016/j.physbeh.2013.03.014