Chances are you've heard someone talking about how blue light ruins sleep. It's true. But have you ever wondered why? Read on to find out.
Light travels in waves of different lengths. It is a form of electromagnetic energy. Only a small portion of the electromagnetic spectrum is visible to humans. Visible light waves range in length from 700 to 380 nanometers. Each color in the rainbow corresponds to a different visible wavelength. Red waves are the longest, and violet waves are shortest.
Humans are sensitive to visible light waves. They act on the body via two pathways: the primary optic tract and the retinohypothalamic tract. The former governs visual perception and response, while the latter governs "circadian, endocrine, and neurobehavioral functions." This is the tract that is most sensitive to blue wavelengths.
Whether blue wavelengths are good or bad for you depends on the timing of your exposure.
Blue light exposure during the day has been shown to increase alertness, treat Seasonal Affective Disorder (SAD), Premenstrual Syndrome (PMS), neonatal jaundice, and acne.
Blue light exposure before bed causes sleep-related problems, especially in teenagers. Blue light waves induce a "circadian delay" by suppressing the secretion of melatonin. That's why confronting your eyes with blue light at night leaves you feeling awake for longer than you would otherwise. Experiments have linked lower melatonin levels with cancer, and desynchronized circadian rhythms with increased circulating sugar levels, inflammation, and obesity. Blue light also reduces the amount of Rapid Eye Movement (REM) sleep you get. REM sleep is restorative, and necessary for memory consolidation.
Lack of sleep negatively impacts your performance, ability to learn new things, and judgement. Chronic sleep deprivation has been linked to shorter lifespans. Wide-spread sleep deprivation also impacts public safety. Drowsy driving is responsible for 100,000 accidents each year in the US. People in their teens and twenties are involved in more than half of these.
In short: Blue light exposure before bed makes it harder to fall asleep and makes your sleep less restorative. To stay healthy and safe we need to sleep at night.
It's important to remember that it's not just our phones and tablets that emit blue light. Blue light is everywhere these days. Because its relatively short wavelengths make blue light seem very bright to humans, it is one of the most energy-efficient colors of light to produce. The bluer the blue, the more energy efficient it is.
To reduce nighttime blue light exposure try the following:
Avoid screen-based media, especially if you hold your media-delivery device close to your face, during the 2 hours before bedtime and in the middle of the night.
Use alarm clocks with red numerals.
Use red night lights.
Replace your blue light emitting compact fluorescents with bulbs that emit warmer light. Choose bulbs rated at 2,700 Kelvin (this means the light they emit will be in the red/yellow end of the light spectrum). Avoid bulbs rated at 5,000 Kelvin or above (blue light territory).
If you must look at a screen before bedtime try blue light blocking glasses or enable "night shift" on your iPhone. Android users can download a blue light blocking app. (NB: Apps that block blue light help, but they are not as effective as glasses or just avoiding blue light altogether.)
Sweet dreams!
Sources:
Environmental Health Perspectives: "What's in a Color? The Unique Human Health Effects of Blue Light"
NASA: "Tour of the Electromagnetic Spectrum"
APA: "Why Sleep is Important"
NPR: "Apps Can Cut Blue Light From Devices, But Do They Help You Sleep?"
Harvard Health Letter: "Blue Light Has a Dark Side"
WebMD Health News: "Is Blue Light Bad for Your Health?"
Scientific American: "Q&A: Why is Blue Light Before Bedtime Bad for Sleep?"