March is Save Your Vision Month, and the American Optometric Association (AOA) is encouraging everyone to be aware of the hazards of light. No, not the intense ultraviolet light that causes welder’s flash or the concentrated beam of a laser, but much more ordinary light: the blue light that is part of the visible spectrum of natural and artificial light.
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Today, we’ll take a look at the composition of light and why blue light is more dangerous than red light.
Are We on the Wrong Wavelength?
Natural sunlight, or “white light,” includes the full spectrum of visible wavelengths, from the low-energy reds, oranges, yellows, and greens (whose wavelengths range from about 700–500 nanometers (nm)) to the higher-energy blues, violets, and turquoises (whose wavelengths range from about 500–380 nm). The visible blues, which make up about one-third of the visible spectrum of light, are sometimes called “high energy visible” (HEV) light, and can be further subdivided into the blue-violet wavelengths (about 450–380 nm) and blue-turquoise (500–450 nm). These are the wavelengths of visible light that make the sky so blue. Just beyond the visible spectrum at the blue end is the “ultraviolet light” that we’ve heard so much about that can cause cataracts and skin cancer.
Beyond offering a didactic appreciation of the beauty of a blue sky, why does this information matter?
Here’s why: Blue light reaches the back of the eye—the retina—very easily. The cornea and lens of the eye block almost all ultraviolet light, and only about 1% of ultraviolet light reaches the retina (although it can cause problems near the surface of the eye, including cataracts, snow blindness, and thickening or discoloration of the cornea). But almost all blue light in the visible spectrum reaches the retina.
That can be a good thing. Blue-violet light exposure has important benefits. The 465–495 nm wavelengths regulate the pupillary reflex, which opens or closes the pupil to regulate the amount of light entering the eye. Blue-violet light also helps to regulate the body’s hormonal circadian (sleep-wake) rhythm. Exposure to light in the range of 470 nm is an effective treatment for seasonal affective disorder (SAD).
But the same light that orders our sleep-wake patterns can also disorder them, making it harder to fall asleep and contributing to less restful sleep when we do sleep. And the highest energy wavelengths of visible light, the blue-turquoise part of the spectrum, are the highest energy light that reaches the back of the eye. As such, light at these wavelengths is the most likely to damage or destroy retinal cells. So when it comes to light exposure, it’s important that we’re all on the right wavelengths.
Bluer than Ever
Humans are adapted to natural patterns of sunlight; exposure to natural light is not generally harmful. But ever since Thomas Edison developed the first incandescent light bulb, our exposure to light has become increasingly unnatural and increasingly skewed toward the blue end of the spectrum. Incandescent bulbs produce the warmest light of any bulb, and halogen bulbs come the closest to natural daylight, but the more energy-efficient bulbs, including fluorescent bulbs and LEDs, produce higher levels of blue light. To make matters worse, our digital device screens are “short wavelength enriched,” meaning the light they give off is much bluer than natural light.
Any light exposure, even to the warm light of an incandescent bulb, has the potential to throw off our circadian rhythm, and nighttime exposure to light has been linked to cancer and other health effects, especially in shift workers. Blue light exposure in particular is linked to both acute and chronic health effects. So, while our future is increasingly bright, we must be aware that it also has a dark side.
Tomorrow we’ll take a closer look at the potential health effects of blue light and how to reduce exposure.