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The Dark Side of Blue Light

After a long day of work, it's tempting to crawl under the sheets and scroll through social media until the wee hours of the night. But as many of us have discovered, it is pretty difficult to fall asleep while holding a bright light 10 cm from our faces. This is concerning since poor sleep increases your risk for obesity, depression, diabetes, cardiovascular disease, and overall mortality.¹⁻² This can be combated by limiting our exposure to blue light before bed.

Visible light is radiated in wavelengths, the width of which determines its color as perceived by the human eye. Blue light has the shortest wavelength and therefore, the most energy. The sun, your smartphone, and indoor lighting are all sources of blue light. Exposure to blue light per se is not necessarily bad for you. During the day, it signals your body to stay awake by increasing wakefulness and reaction time.³ In contrast, the absence of blue light during the night signals your body to fall asleep. This mechanism was adapted to synchronize your sleep-wake cycle to the sun's orbit.⁴ But unlike our pre-industrial ancestors, modern people are exposed to blue light via digital devices and indoor lighting long after the sun sets. This tricks your body into thinking that it is daytime at night which makes it difficult to fall asleep and leads to non-restorative sleep.⁵⁻⁶

The best way to combat the negative effects of nighttime blue light exposure is to limit your usage of digital devices before bed. This may be unrealistic for some of us that have to work late at night. Fortunately, electronic manufacturers have taken this into account and many digital devices today offer a blue light blocking function. But this is ineffective unless it is accompanied with a reduction in brightness.⁷ What are your tips for getting a good night's rest?


  1. Cappuccio, F. P., Cooper, D., D’Elia, L., Strazzullo, P., & Miller, M. A. (2011). Sleep duration predicts cardiovascular outcomes: A systematic review and meta-analysis of prospective studies. European Heart Journal, 32(12), 1484–1492.

  2. Grandner, M. A., Jackson, N. J., Pak, V. M., & Gehrman, P. R. (2012). Sleep disturbance is associated with cardiovascular and metabolic disorders. Journal of Sleep Research, 21(4), 427–433.

  3. Vandewalle, G., Maquet, P., & Dijk, D. J. (2009). Light as a modulator of cognitive brain function. Trends in cognitive sciences, 13(10), 429–438.

  4. Wahl, S., Engelhardt, M., Schaupp, P., Lappe, C., & Ivanov, I. V. (2019). The inner clock—Blue light sets the human rhythm. Journal of Biophotonics, 12(12).

  5. Duffy, J. F., & Czeisler, C. A. (2009). Effect of Light on Human Circadian Physiology. Sleep medicine clinics, 4(2), 165–177.

  6. Holzman D. C. (2010). What's in a color? The unique human health effect of blue light. Environmental health perspectives, 118(1), A22–A27.

  7. Nagare, R., Plitnick, B., & Figueiro, M. G. (2019). Effect of exposure duration and light spectra on nighttime melatonin suppression in adolescents and adults. Lighting Research & Technology (London, England : 2001), 51(4), 530–543.

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