This is part four in a four-part series guest-written by nationally recognized blue light expert, Gary Morgan, OD.
Over the course of the past three blog posts, we have examined why closer working distance, large pupils, and clear crystalline lenses contribute to children being more vulnerable to the adverse effects of blue light.
So with the “why’s” out of the way, let’s examine the “how’s,” as in, how to help children reduce their blue light exposure and combat digital eye strain.
Reducing Blue Light Exposure: A Two-Pronged Approach
There are two ways to minimize the amount of blue light reaching the retina. We can either decrease the amount of blue light being emitted from the source, or we can filter blue light in front of the eyes. Of course a third option would be to limit our children's screen time, but this is becoming more difficult as smartphones and tablets are becoming the primary form in which children learn, socialize, and relax. So let's explore reducing blue light from the sender and to the recipient:
1. Decreasing Blue Light at the Source
There are a few ways to decrease blue light emitted from smartphones and tablets. The easiest and most direct way would be to turn down screen brightness. The website Fluxometer.com shows the effect of doing so across the entire visual spectrum for a variety of devices, and equates the light given off by the device as a percentage as bright as daylight.
Some screen protectors now include blue light filtration. However, information on their blue light transmittance was unavailable at the time of this article. As will be discussed in a moment, without a transmittance curve, it is impossible to know exactly what these filters are doing.
There are apps available to decrease the amount of blue light emitted from phones and tablets. Some of these apps allow you to program your devices to automatically reduce blue light emission at a specified time of day, as well as adjust how much blue light is filtered out. A good demonstration of this can be seen in a short video put together by Thomas Gosling OD:
2. Reducing Blue Light in Front of the Eyes
The blue-light-reducing lens category has exploded over the past five years. In 2012, there was one company specifically marketing this type of lens. Today, there are nearly 100 different blue-filtering lenses available from manufacturers large and small. These products work by absorbing, reflecting, or both absorbing and reflecting varying wavelengths of blue light.
Blue Light Reducing Lenses and Coatings
Four types of optical products have been proven to reduce blue light exposure:
Understanding Blue Light Reduction Percentages
You’ve likely seen (or will see) different companies claiming their products reduce a specific percentage of blue light. However, the question to ask is how much blue light does a particular product filter at different points in the blue light spectrum? The answer is found in looking at a product’s transmittance curve. Below is the transmittance curve for TechShield Blue.
Note that as you move along the x-axis, wavelength increases, and as you move up the y-axis on the left, transmittance increases. So at about 400nm, TechShield Blue reduces blue light transmittance by approximately 80%. And at about 420nm, it reduces transmittance by approximately 20%. This is important because transmittance at different wavelengths can have varying effects.
Examining Overall Blue-Light Reduction Claims
As previously noted, some companies claim a specific percentage of overall blue light reduction for their products. This is disingenuous because transmittance varies by wavelength. For instance, the shortest wavelengths of blue light have the greatest impact on visual performance, that is, they are the most myopically defocused in front of the retina causing the greatest amount of chromatic aberration. If a particular lens transmittance is 60% at 400nm while another lens is 18%, clearly the lens transmitting 18% at 400nm will have a greater capacity to relieve digital eye strain.
Throughout this series we have looked at how short arms (proximity), as well as pupil size and crystalline lens clarity (retinal illumination) make children more vulnerable to the effects of blue light from handheld digital devices. In closing with this section on lenses, it’s important to emphasize that eye care providers are fully informed on the exact benefit of the products being dispensed. Insist on transmittance curves for the lenses you prescribe to reduce blue light exposure.
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