Which colour, brightness and rate of flicker drive the brain hardest (Lee 2021)
Red light entrained gamma most effectively, then white. Brighter was stronger, but the brightest setting caused more side effects. Flicker at 34–38 Hz was stronger and spread further than 40–50 Hz.
The question: What colour, brightness and rate of flickering light produces the strongest gamma-band response?
| Type of study | Experiment |
|---|---|
| Who took part | Young adults (number not given in the abstract) |
| What was done | Compared four colours (white, red, green, blue), four luminances (10 to 700 cd/m²) and ten flicker rates from 32 to 50 Hz, with EEG and a record of side effects. |
| How much weight it carries | Mixed evidence |
What it found
- Red light entrained gamma waves most effectively, followed by white.
- 400 and 700 cd/m² entrained more strongly than 100 and 10 cd/m².
- 700 cd/m² caused more moderate-to-severe adverse effects than the other levels.
- 34–38 Hz entrained more strongly, and spread further beyond visual cortex, than 40–50 Hz.
- The paper notes that 40 Hz light failed to reduce amyloid in a study of six patients.
Limits
- A brain response, not a benefit.
- Young healthy adults; eyes-open LED stimulation.
- Side effects rose with brightness.
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
- Lee, K., Park, Y., Suh, S. W., Kim, S. S., Kim, D. W., Lee, J., Park, J., Yoo, S., & Kim, K. W. (2021). Optimal flickering light stimulation for entraining gamma waves in the human brain. Scientific Reports, 11. doi.org/10.1038/s41598-021-95550-1