The more you know about light, its composition and its impact on human physiology, the better equipped you will be to make decisions about your eye health and that of your family
Light is made up of electromagnetic particles called photons that travel in waves. These wavelengths of visible and non-visible light are measured in nanometers (nm), and, in general, the shorter the wavelength, the higher the energy. Together these wavelengths make up the electromagnetic spectrum.
The human eye perceives only the Visible Light portion of the electromagnetic spectrum, which ranges from 380nm to 700nm and is represented by the colors violet, indigo, blue, green, yellow, orange and red. Blue light, also know as high energy visible (HEV) light, has the shortest wavelength of visible light (380nm to 500nm), and therefore produces the highest amount of energy. HEV blue light produces both benefits and concerns for our eyes and overall health.
Humans evolved throughout the millennia with only one source of light – the sun. One portion of sunlight – the blue-colored bands ranging from 380nm to 500nm – is known as HEV blue light and is particularly beneficial in modest amounts. In general, about 25% of sunlight is blue light, although the actual amount at any point in time depends on your latitude and the angle of the sun during a particular season, the time of day, your total time outdoors.
Because of its higher energy, blue light penetrates deep into our eyes to the retina. Once it reaches the retina, blue light plays an important role in the body by suppressing the production of melatonin, which increases our alertness in the morning and maintains our circadian rhythms. Similarly, as the sun sets in the evening, our eyes take in less blue light, which once again signals the production of melatonin and enables us to sleep. Research has also shown that blue light boosts alertness, helps memory and cognitive function, and elevates mood.
Because too much HEV blue light can have negative effects on the human body, humans have instinctively developed ways to limit the amount of blue light that reaches our retinas, including pupil constriction, reflexively looking away from the sun, and squinting in bright sunlight.
Anterior structures of the adult human eye (the cornea and lens) are very effective at blocking UV rays from reaching the light-sensitive retina at the back of the eyeball. But HEV blue light is different, with much of it passing through the cornea and lens and reaching the retina at the back of the eye. Studies suggest that, over time, cumulative exposure to the HEV blue light could cause specific long-term damage to your eyes:
Although humans have evolved to accommodate proper amounts of beneficial blue light from the sun, we are only now recognizing that man-made digital light presents new concerns for the health of our eyes. Today, artificial LED-produced blue light is nearly inescapable, and is presented through dozens of man-made sources, including streetlights, interior lighting, and through our many digital devices such as smart phones, tablets, laptops, and desktop monitors. This latter category of digital devices is of particular interest because we are often positioned very close to our device screens, day after day, for many hours at a time.
Perhaps the most at-risk groups for blue light impacts are children and teens, who not only consume massive amounts of digital screen time, but whose eyes are not yet fully developed to mitigate exposure to blue light. Similarly, we lose protective melanin cells as we age, making the elderly particularly susceptible to increased incidences of age-related macular degeneration. For all age groups, too much digital blue light late at night (e.g., reading a novel on a tablet or e-reader, or spending time on social media at bedtime) can disrupt sleep cycles, potentially causing sleepless nights and daytime fatigue.
American Macular Degeneration Foundation
Ultra-violet and Blue Light Aggravate Macular Degeneration
Why is Blue Light Before Bedtime Bad for Sleep?
Blue Light and Your Eyes
Review of Optometry
Seeing Blue: The Impact of Excessive Blue Light Exposure
Handling the Blues
How to Protect Your Eyes from the Negative Effects of Digital Devices and Blue Light