How much light gets through a closed eyelid (Bierman 2011)
Very little: on average the eyelid cuts light between 450 and 650 nm by a factor of about a hundred, and it blocks short wavelengths (blue) far more than earlier figures suggested.
The question: How much light, and which colours, reach the eye when it is closed?
| Type of study | Measurement study |
|---|---|
| Who took part | Adult volunteers (number not given in the abstract) |
| What was done | Measured how much light of each visible wavelength passes through the closed human eyelid, and modelled it from the absorption and scattering of skin. |
| How much weight it carries | Strong design |
What it found
- Mean optical density of the eyelid from 450 to 650 nm was 2.1 (about 1% of the light gets through), with a spread between people of roughly a factor of ten.
- The eyelid blocks short wavelengths much more strongly than previously published; it behaves as a red-pass filter.
- Skin pigmentation was a poor predictor of how much light got through; eyelid thickness and wavelength-independent tissue mattered most.
Limits
- A measurement of the eyelid, not of any effect of light on a person.
- Large differences between individuals.
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
- Bierman, A., Figueiro, M. G., & Rea, M. S. (2011). Measuring and predicting eyelid spectral transmittance. Journal of Biomedical Optics, 16(6), 067011. doi.org/10.1117/1.3593151