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Light & Sleep: Is It Best to Sleep in Pitch Darkness? Part 4

As a general rule, it is best to sleep in as much darkness as possible. Pitch darkness reduces potential distractions and disruptions to sleep.

Sleeping with a light on interferes with sleep cycles and causes more fragmented sleep, and these downsides may be greatest in the few hours before waking up.

Research demonstrates that closing your eyes isn’t enough10; your eyelids can’t block sufficient light. The effects on circadian rhythm can occur even with low levels of indoor light and closed eyes.

In addition to sleep quality, there are other reasons why research indicates that it’s best to sleep in pitch darkness:

  • Eye strain: Even low levels of ambient light during sleep have been associated with eye strain11, resulting in soreness, tiredness, and discomfort in the eyes, as well as greater difficulty focusing.
  • Weight gain: Keeping lights on during sleep appears to affect circadian regulation of metabolism, increasing the risk of weight gain even if sleep itself is not disrupted. In one study over a five year period, women who slept with a light or TV on were considerably more likely to gain 10 pounds or more12, even after controlling for factors relating to their diet and exercise habits.
  • Cancer risk: One observational study found an association13 between people whose homes had high levels of artificial light at night and their risk of breast and prostate cancers. This study did not demonstrate causation, and further research is necessary to understand this correlation.

The diverse potential consequences of excess artificial light in your bedroom reflect that light exposure may throw off circadian rhythm and its vital role in promoting numerous elements of physical and mental health.




10. Figueiro, M. G., & Rea, M. S. (2012). Preliminary evidence that light through the eyelids can suppress melatonin and phase shift dim light melatonin onset. BMC research notes, 5, 221.

11. Suh, Y. W., Na, K. H., Ahn, S. E., & Oh, J. (2018). Effect of Ambient Light Exposure on Ocular Fatigue during Sleep. Journal of Korean medical science, 33(38), e248.

12. Park, Y. M., White, A. J., Jackson, C. L., Weinberg, C. R., & Sandler, D. P. (2019). Association of Exposure to Artificial Light at Night While Sleeping With Risk of Obesity in Women. JAMA internal medicine, 179(8), 1061–1071. Advance online publication.

13. Garcia-Saenz, A., Sánchez de Miguel, A., Espinosa, A., Valentin, A., Aragonés, N., Llorca, J., Amiano, P., Martín Sánchez, V., Guevara, M., Capelo, R., Tardón, A., Peiró-Perez, R., Jiménez-Moleón, J. J., Roca-Barceló, A., Pérez-Gómez, B., Dierssen-Sotos, T., Fernández-Villa, T., Moreno-Iribas, C., Moreno, V., García-Pérez, J., … Kogevinas, M. (2018). Evaluating the Association between Artificial Light-at-Night Exposure and Breast and Prostate Cancer Risk in Spain (MCC-Spain Study). Environmental health perspectives, 126(4), 047011.


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