Blue light CAN damage the eyes. But on the flip side, you don’t need to worry about blue light damaging the eyes. Sound confusing? Let’s cover why this is the case.
Excess exposure to blue light can damage your cornea and lens. Especially concerning, it can damage your retina and increase the risk of macular degeneration. Fortunately, during our routine day we do not have enough exposure to cause these issues. Even when on our computer and phones.
In fact, when you are outside during the day, you receive much more blue light without developing any issues to the eyes. Thus, there is no need to stress over the amount of blue light you are receiving from your screens.
What Is Blue Light?
All light exists on a spectrum of electromagnetic radiation. On this spectrum is visible light. This is the light that you can see. Remember learning about the rainbow? Those are all the colors of the visible light spectrum that you can see. Rainbows exists because each of these colors has a different wavelength. White light (which contains all the colors) spreads out when passing through water droplets in the air (or a prism), causing a rainbow.
At the longer end of the wavelength we have our reds, and yellows. On the shorter end of the spectrum we have our blues and violets.
Electromagnetic spectrum of light; image by Philip Ronan, CC BY-SA 3.0, via Wikimedia Commons
In general, shorter wavelengths of light and electromagnetic waves contain more energy. In addition to blue light, another important short wavelength light is ultraviolet light. Yep. This is the same light which causes sunburns.
Ultraviolet light can also cause damage to the eye. With high exposures, UV light can cause sunburned eyes or photokeratitis. Over the long term, exposure to ultraviolet light can contribute to the development of cataracts.
And in some ways, blue light is similar to ultraviolet light.
The Damage From Blue Light
Short wavelength light is full of energy. As this light hits different structures, it can pass off some of that energy. This extra energy can either damage the cell enough to cause it to die or it can generate oxidation (which still will cause damage).
And this can occur from the front to the back as blue light passes through the eye.
The Cornea
The first structure of the eye that blue light hits is the cornea. And the first first layer of the cornea is the skin on the surface of the eye called epithelium. This epithelium protects our cornea.
As the first structure on the pathway of light, blue light hits this epithelium first. And the epithelium can absorb this blue light. This can cause the epithelial cells to die and oxidation from the blue light can cause extra inflammation on our eye. This is very similar to sunburned eyes from ultraviolet light (but to a smaller degree).
Luckily this damage isn’t permanent. The epithelium does regenerate.
So what does this mean? Well, if the epithelium is damaged, this creates something known as ocular surface disease. You know what else causes ocular surface disease? Dry eye.
So effectively, blue light can make dry eye worse. Or at least it can make your eyes feel more irritated.
The Lens
As we get further and further into the eye, less blue light penetrates. As short wavelength light goes through a structure, some of it is absorbed. (In fact, the shortest wavelengths of ultraviolet light from the sun can’t even make it through our atmosphere). Thus, some blue light is absorbed by our cornea and doesn’t even make it to our lens.
But a significant amount of light can still make it to the lens.
The lens has one key role: to remain transparent. Within the lens are specialized proteins called crystallins which are designed to be transparent. Blue light that hits the lens can once again cause oxidative stress in the lens. And this oxidative stress can damage the proteins of the lens.
But our lens actually has some built in protection against light. These defenses against light helps prevent the oxidative stress from ruining the transparency of the lens. But as these defenses break down over time, persistent exposure to light can cause the lens to go cloudy, affect the vision and become a cataract.
Much of this has been studied evaluating the link between ultraviolet light and cataracts. And there is still much to learn. For example, it isn’t quite clear if our natural defenses to light break down because of exposure to light or just simply with age. But because blue light can also cause oxidative stress (although less than with ultraviolet light), blue light can potentially damage the lens.
The Retina
The damage that blue light can cause to the retina is perhaps the most alarming. This is because this damage can lead to permanent vision loss.
The retina exists in different layers. On the surface of the retina are the photoreceptor cells. These cells respond to light to send signals to the brain. Underneath these cells is the retinal pigment epithelium. This layer supports those photoreceptor cells.
The common condition of macular degeneration involves a breakdown in the retinal pigment epithelium. This can create bleeding, scarring and permanent vision loss. So of course, we want to prevent this.
High amounts of blue light WILL damage the retina. In fact, not only will blue light damage those photoreceptor cells and cause them to die. The oxidative stress from blue light will also damage the retinal pigment epithelium. This can increase the risk of macular degeneration.
This all sounds like bad news. Right?
Why Blue Light Isn’t A Problem To Eyes
Not all light sources are created equal.
Take for instance, the sun. The sun is bright! Your cell phone is NOT as bright as the sun. If you look directly at the sun you WILL damage your eyes (so DON’T look at the sun).
When we talk about light sources, we can measure something called luminance. This refers to how much light is emitted from something. Subjectively we call this brightness.
Bright sun in the sky; Photo by CHUTTERSNAP on Unsplash
The sun has a very high luminance. At high noon, the luminance of the sun is 1,600,000,000! But of course you aren’t looking at the sun so let’s compare to something else. If we have an incandescent light bulb with a clear glass bulb, the luminance value if you are staring at the filament is still high, around 2,500,000.
If you were to stare at this light bulb filament long enough, you will end up damaging your eyes. Again, don’t.
The luminance of something, when combined with how long we are looking at something determines our exposure to light.
With a high luminance value, such as the sun, you don’t need to look very long to damage your eyes. With a lower luminance value, more time needs to elapse before your eyes are damaged. But we have a reflex as humans which gives us an aversion to looking at light. This natural reflex often protects us from looking at a light too long.
So let’s look at a few more luminance values:
When you are outside on a nice day with clear blue skies. The luminance value of the sky around you is around 8,000. If the day is cloudy the luminance value is around 2,000.
Finally, let’s look at our device screens (in which much of the concern over blue light is being directed). The luminance of computers, tablets and cell phones falls around 200. ****That’s about 40x less light than you receive on a nice clear day outside!
You just simply don’t get high amounts of blue light exposure from screens compared to what you get just being outside.
But studies show blue light damaged the retina…
It’s difficult to completely replicate the way our eyes work as humans in a study.
One challenging feature to replicate is the fact that light must pass through multiple structures before it reaches the retina. Blue light doesn’t hit the retina directly. It must pass through the cornea and the lens.
The cornea will absorb some of this blue light. The lens will absorb even more. In fact, as the lens ages and gets cloudy, it will absorb even more of this blue light. The lens and the cornea help prevent blue light from even reaching our retina, reducing damage from the blue light that we do see.
Many of the studies look at cell cultures. They take retinal cells and put them in a petri dish before performing the experiments. Not necessarily a bad thing; its really one of the main ways we can perform studies on human cells. And studying the effect of something helps progress science and understanding of human disease and lead to new treatments. But there are limits to how these studies can be applied to real life.
Blue Light And Circadian Rhythm Problem
Ok, so the blue light from your cell phone isn’t going to damage your eyes. It just isn’t bright enough. So what does it do?
Well, the blue light can affect your ability to fall asleep. Our sleep wake cycle is regulated by certain hormones. One of these in particular is the hormone melatonin. When nighttime approaches, the production of this hormone increases and this help allow us to fall asleep.
Exposure to light can suppress the production of this hormone. Of all light, blue light has the largest effect. During the day this is normal since we want to be awake during the day. But too much blue light before bedtime can suppress melatonin and throw off your sleep-wake cycle or circadian rhythm.
This is the reason to avoid blue light. Not damage to the eyes, but improved sleep.
Summary
Blue light can actually lead to damage to the eyes. The cornea, lens and retina all can be damaged from exposure to high amounts of blue light. But fortunately during our routine day, we just don’t have these high exposures and don't have to worry about this damage in normal circumstances.
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