Question: [A short introduction to the question may be useful: This reader had been experiencing a deteriorating problem of sensitivity to computer screens: eye strain, blurred vision, … Changing computer display settings to dark colors helped but did not solve the problem. The different (unspecified) low blue light filtering methods (excluding GLARminŸ Tester kit) hadn’t helped either. After seeing GLARminŸ blue light filter testing glasses the reader wondered if there was a similar product to test ones’ sensitivity to other light colors (wavelengths).

I recommended to look at other possible causes of computer screen light sensitivity and also suggested Irlen. Unfortunately, Irlen had no testing facility near this reader. Subsequently, I suggested a Swatchbook of filter gels, while expressing concerns about the ability of a non-expert to perform the tests well. A few weeks later, after having purchased and tried the filter gels, the reader came back with this question:]

I now realize that the low blue light filtering techniques that I had previously tried were not that effective. This has made me consider that my problem may indeed be related to low blue light after all. I am having some success with the filters that I bought (especially those that filter out the lower end of the visible spectrum – low blue light). The one issue I’m having is that visual acuity is also reduced by the filters. This makes a true comparison of their benefit difficult. I was wondering if you could comment on how your low blue light filtering kit [GLARminŸ Tester] is in terms of retaining clarity of vision?

Disclaimer: I am NOT a vision scientist nor a physician but a more computer glare and light-sensitive person, hence my interest in low blue light filters, eye strain, blurred vision, acuity and light sensitivity.



Visual acuity & low blue light filters in general

Any filter (eyeglasses lenses, contact lenses, screen protector) in front of your eyes reduces acuity somewhat.

The amount of light available to your eyes is reduced. Even the best ophthalmic lenses have overall visual light transmission (VLT) at about 90-95% meaning that they make the light look dimmer by about 5-10%.

Moreover, even filters with the highest refractive index, at least minimally, distort the image.

Hence, the use of any type of filter is a trade-off between its benefits and costs (negative side effects), the loss of light available and image distortion/blurred image among them. It only makes sense to use a filter when the benefits outweigh the costs. And this trade-off is unique to each person.

There are several possible negative side effects of different filters: discomfort in using them, monetary cost, aesthetics, color distortion, refraction– and reflection-related distortions of light passing through any filter which reduce acuity, blur vision and often lead to eye strain.


Veiling glare, Blurred vision, and eye strain

One type of distortion that I’d like to caution you about (it is often overlooked) is veiling glare. It reduces acuity by blurring your vision thus leading to eye strain. Make sure you get rid of it (or minimize it to the extent possible).

Veiling glare is the reflections from the surface of a filter back into the eye of its user. Low blue light filters are no exception.

Veiling glare is usually not noticed because one is focused on the digital screen beyond the filter (glasses, screen protector).

However, veiling glare can blur your vision (reduce acuity) and put considerable strain on your eyes that continuously try to make the image on your digital screen clearer – trying to see as if through a veil. Evidently, your eyes have no chance of success unless veiling glare is removed.

You can observe veiling glare as a faint ghost image on the surface of your lenses.

See this article for more detail on veiling glare and possible solutions.


Low blue light filters and vision acuity

Blue light filters generally reduce available light to the eye by more than clear filters (lenses) because they selectively block low blue light (400-500nm) more, quite a lot, or completely, as for example GLARminŸ Tester Filter 2:

Low blue light filter, Blurred vision, eye strain

Weaker blue light filters and regular clear UV400 lenses only block 100% of light up to say 400nm or just a bit more, as for example Filter 7 of Tester kit:

Low blue light blurred vision eye strain Filter 7

Hence, the overall visual light transmission (VLT) of stronger blue blockers tends to be lower (as long as transmission above 500nm is similar).

Note: Night driving with low blue light filters is discouraged because our night (low light) vision/acuity principally depends on blue light. Thus if blue light is blocked considerably our vision at night is a lot dimmer than it would be in daytime. (VLT at 80% or above is required for category 0 ophthalmic lens which may be used also for night driving).

However, despite lower VLT, a blue light filter in front of your eyes may improve your sharp vision because blue light disturbs your precision vision.


Low blue light filter paradox: Acuity is Increased although available light is Reduced

For a long time, scientists were puzzled because the research into the benefits of low blue light filters was inconclusive. The explanation was finally found in the inter-personal variability of the blue light blocking effectiveness of our macular pigment. When macular pigment was taken into account, the benefits of low blue light filters became clear: selective short wavelength light absorption attenuates the effects of chromatic aberration and light scatter thus improving acuity and visibility [The Visual Effects of Intraocular Colored Filters (2012)].

low blue filter - macular pigment eye anatomy


People with hi/strong macular pigment find blue blockers disturbing

At one extreme (far right of the image below) there are those whose macular pigment is very effective at filtering blue light. If measured, they would have a high macular pigment optical density (MPOD) score.

As you might expect, these people have no need for an additional low blue light filter because little (if any) blue light is reaching their sharp vision photoreceptors hidden behind their macular pigment. This means that, their precision vision is not being disturbed by low blue light.

Therefore, if they add an external low blue light filter, their visual acuity can only get worse due to lower quantity of light reaching their photoreceptors and other light distortions inherent in any filter.

blurred vision, eye strain MPOD low blue light


People with low/weak macular pigment love external low blue light filters

At the other extreme (far left in the image above), there are those with low macular pigment (MPOD score). Since their macular pigment hardly filters any low blue light, plenty of it is reaching their sharp vision photoreceptors only to cause blurred vision and eye strain.

When these people use external low blue light filters, they find their vision/acuity enhanced because an external blue light filter blocks the blue light that their macular pigment is not blocking.


Most people fall somewhere in between: The question is Where?

There is a continuum of macular pigment effectiveness going from hi to low. As you can see in the image above, a sizeable proportion of the US population has ineffective macular pigment. (The data is not significantly different in other first world populations).

The trouble is that, unless you know your MPOD score, you cannot say with any level of certainty whether a low blue light filter will help you or not. Unfortunately, measuring MPOD is not the most easily accessible outside a few specialized research labs.

Hence, the best way to find out whether a blue light filter will help you or not is by trying.


Visual acuity & blue light filters from the GLARminŸ Tester kit

​The Tester kit is intended to help you discover which blue light filter (if any) will help you improve acuity and, subsequently, also your visual comfort when viewing digital screens.

GLARminŸ Tester comes with 8 different blue light filters. Each blocks a different amount of blue light at different wavelengths. The filters are also compared to other commercially available blue light filters on the basis of transmission such that one can more easily find an appropriate, permanent solution to their problem with low blue light.

The Filters in the Tester kit are fabricated for consistency in spectral transmission. They are not fabricated as high-end ophthalmic lenses to minimize distortions of light passing through them. However, in my subjective use and testing, I haven’t noticed any issues with respect to acuity loss.

Perhaps GLARminŸ Tester users might want to add their observations with respect to eye strain, blurred vision, and acuity when using low blue light Tester kit. Feel free to do so in the comments below, or by writing to me!?