Blue light filter selection is complicated. A blue filter may help you with many problems: computer eye strain (computer vision syndrome), LED & fluorescent light sensitivity, sleep disorder, age-related macular degeneration (AMD), light sensitivity (discomfort glare), visual acuity… But not every blue filter will produce optimal results given the specifics of your blue light sensitivity problem. The chaos of hype marketing terminology often hides more than it reveals which further complicates the selection process. Read on to find out: which wavelengths your blue filter should absorb/block, by how much, how to compare bluelight filters…
The two simple rules for your blue filter selection proposed below are principally derived from two properties of human vision system:
(1) Macular pigment spectral absorption curve; for problems related to (blue) light sensitivity, glare and glare-related (computer) eye strain
(2) Spectral sensitivity curve of melanopsin; for sleep disorders
The two properties are first explained to derive the decision criteria. Then several blue filters are evaluated.
Blue filter terminology
To filter, block or absorb light are used interchangeably as synonyms to denote the proportion of light not transmitted (passed) through a filter.
If a filter transmits x% (e.g. 40%) of light, it filters/blocks/absorbs 100%-x% (e.g. 100%-40%=60%). Conversely, if a filter blocks/filters/absorbs y% (e.g. 20%) of light, its transmission is 100%-y% (e.g. 100%-20%=80%).
Disclaimer: My interest in blue light is due to my problems with light sensitivity (photophobia), discomfort glare, and computer eye strain. I am not a vision scientist.
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The science on blue filter effects
This section draws principally from two scientific papers:
- a comprehensive review on The visual effects of intraocular colored filters (2012) which includes a lengthy list of blue filter literature, and
- Enhancing performance while avoiding damage: A contribution of macular pigment (2013).
To avoid repetition citations to these two reports (but not others) are avoided.
(1) Blue filter vs. light sensitivity, AMD, glare, glare related (computer) eye strain…
Light avoidance or pain (discomfort) we feel in excessive brightness is our protective mechanism against light damage, particularly AMD. Within the visible part of the electromagnetic spectrum (wavelengths from about 400nm to about 700nm) the principle “troublemaker” is short wavelength light (violet and blue light) from about 400nm to about 500nm. It is usually referred to simply as blue light.
Detrimental properties of blue light
When compared to longer visible wavelengths blue light:
- carries considerably more energy such that it can penetrate deeper into the eye and cause tissue damage at lower light intensity levels
- degrades vision through greater scattering and aberrations thus leading to glare disability and discomfort glare at lower light intensity levels
Macular pigment: Our natural blue filter
The natural countermeasure to these undesirable effects of blue light are two intraocular blue filters. The crystalline lens shields entire retina from most of the light below 400nm (violet and UV light). Its absorptive capacity falls sharply to near 0 by about 450nm.
The second blue filter is more interesting from the perspective of blue light sensitivity. Macular pigment protects only the macula, a tiny area (about 1%) of the retina, where our vision is sharpest and where our retina is by far the most sensitive to light induced pain. A healthy macular pigment peak absorption is ~460nm and filters blue light considerably from ~440nm to ~480nm. Outside these boundaries its absorption relatively quickly drops to 0 (see image above).
Macular pigment deficiency
Macular pigment advantages over an external blue filter
An external blue filter is an obvious solution to low MPOD. It brings several benefits: reduction of intraocular scatter, lowering of glare discomfort (photophobia) threshold, improved photostress recovery and glare disability.
However, a major drawback to external blue filters is the loss of input to photoreceptors (they have less light to “work with”) which may be critical in low-light conditions. Macular pigment covers only the photoreceptors for day vision (bright conditions) at the macula (principally long wave – L and medium wave – M cones). Conversely, an external blue filter shields all of the retina, including the photoreceptors (rods) for vision in low-light conditions, which are most sensitive in the upper blue light and green range (~440nm to ~540nm).
Hence unlike macular pigment an external blue filter considerably reduces input to night vision photoreceptors. This is the principle reason why tinted lenses/glasses are discouraged for night driving. It is also why improving your macular pigment through diet (or dietary supplementation) is the preferred solution over a longer run.
A good external blue filter should simultaneously maximize visual light transmission while minimizing blue light transmission
A recently patented Wertheim Factor summarizes well all of the above. It was invented to facilitate blue filters comparisons. Wertheim Factor represents the fraction of the damaging high-energy spectrum blocked by a filter compared to the visible transmission of the filter. The resulting figure ranges from 0 to about 0.5. A high Wertheim Factor indicates a filter that blocks well in the UV-violet-blue range while also transmitting well in the green-yellow-red range that is most easy to see and least damaging to the photoreceptors.
Unfortunately there is currently only one vendor – Reading Glasses ETC (Disclosure: commission link) – that supplies Wertheim Factor data for their blue filter lenses.
(2) Blue filter vs. sleep disorder
If your blue light related problem is sleep, than your blue filter decision criteria will be slightly different. Blue light is used by our brain to adapt our sleep-wake cycle to day-night cycle (for more info, view explaination by a leading scientist). Until very recently in men’s evolution this worked reasonably well, because sun’s light was the only source of intense light, blue light in particular – see below. (The only environments that did not facilitate sleep of sufficient length and quality were areas far from the equator with late sunsets and early sunrises in summertime).
However, the developed world has become less sleep-friendly due to the widespread adoption of light sources with relatively high blue light intensity. Light-emitting diode (LED) and fluorescent bulbs have become very common light sources, some of them with very high blue light content (Levels of visual stress in proficient readers: Effects of spectral filtering of fluorescent lighting on reading discomfort; 2015). Moreover, in the evenings, just before bedtime, we increasingly use LED digital display devices: computers, TVs, smartphones, tablets… (Blue blocker glasses as a countermeasure for alerting effects of evening light-emitting diode screen exposure in male teenagers; 2015. Protective effect of blue-light shield eyewear for adults against light pollution from self-luminous devices used at night; 2016).
As shown below the sensitivity of melanopsin (the receptor of non-visual information related to sleep/wake cycle) peaks around 480nm, is high between ~430nm and ~520nm and practically 0 above 550nm. Filtering blue light up to these wavelengths should help you go to sleep faster (if you are an evening type) or sleep longer (if you are a morning type).
Summary: Two simple blue filter rules
(1) Blue filter vs. light sensitivity (AMD, glare and glare associated eye strain):
(2) Blue filter vs. sleep disorder:
Block sufficiently (depending on your sensitivity) wavelengths near 480nm (±40nm); (Use only 2-4 hours before bed time. Such blue filter will considerably reduce your low-light vision – see spectral sensitivity of Rods above).
Using the same blue filter for light sensitivity as for sleep disorder might be an overkill.
Similarly, a 0% blue light transmission (blocks 100% of blue light) up to a certain wavelength might be an overkill – unless you’ve determined you have highly blue light sensitive eyes.
Blue filters evaluated and compared
The table below should help you gain an understanding of how to evaluate blue filters. For demonstration purposes, an LED source (Thinkpad T440s at 6500K CCT) and a fluorescent source (Westcott CFL at 4500K CCT) were chosen. Click on images, to enlarge. Data source: fluxometer – many more options of filters, light sources and related data available there).
The filters are ordered roughly according to color distortion (from less to more) and mostly also from lower to greater blue light absorption. Note that the background on spectral diagrams changes: it approximately shows what white looks like through the given blue filter.
Transmission: Near 460nm – High; Near 480nm – High; VLT: ~98%. Suitability: Minimal blue light protection. Filter: iLLumiShield Screen Protector.
Transmission: Near 460nm – High; Near 480nm – High; VLT: ~86%. Suitability: Minimal blue light protection. Filter: Tech Armor RetinaShield Blue Light Filter Screen Protector.
Transmission: Near 460nm – Moderate; Near 480nm – Moderate; VLT: ~62%. Suitability: For migraine, blepharospasm & fluorescent light sensitivity**; For moderate sleep disorders. Filter: Axon Optics FL-41 light sensitivity/ migrane relief glasses (indoor lens).
Transmission: Near 460nm – Moderately-high; Near 480nm – High; VLT ~97%. Suitability: For non-glare/light sensitive; Not for sleep disorder. Filter: Gamma Ray computer/gaming glasses.
Transmission: Near 460nm – Moderate; Near 480nm – Moderately-high; VLT ~96%. Suitability: For mildly-glare/light sensitive; For minor sleep disorder. Filter: Gunnars (computer, gaming and prescription Rx).
Transmission: Near 460nm – Low; Near 480nm – Moderate; VLT: ~92%. Suitability: For more glare/light sensitive; For minor sleep disorder. Filter: 3M safety glasses.
Transmission: Near 460nm – Complete; Near 480nm – High; VLT ~69%. Suitability: For more glare/light sensitive; For severe sleep disorders. Filter: LowBlueLights eyeglasses.
Transmission: Near 460nm – Complete; Near 480nm – Complete; VLT ~47%. Suitability: For more glare/light sensitive; For severe sleep disorders. Filter: Melatonin Shades.
Transmission: Near 460nm – Complete; Near 480nm – Complete; VLT ~51%. Suitability: For more glare/light sensitive; For severe sleep disorders. Filter: UVEX SCT Orange safety glasses.
** FL-41 tint was designed initially for fluorescent light sensitivity and has also been shown to alleviate Migraine and some Benign Essential Blepharospasm symptoms (Diagnosis, Pathophysiology, and Treatment of Photophobia; 2016). TheraSpecs (non-commission link) is another company that offers FL-41 tint on their migraine relief and fluorescent light sensitivity eyeglasses. You can also buy TheraSpecs on Amazon (commission link). Spectral transmittance may be found here.
For more options in blue light filtering glasses see post Best blue blockers in style and light filter specs.
The best way to know for sure which filter might work best for you is to try. Since testing is rarely possible you might consider a simple DIY test of blue light sensitivity or recur to intuitive colorimetry (particularly if you feel that a blue filter doesn’t help you – your vision might be asking you to filter out different wavelengths to feel comfortable and avoid visual stress).
Blue filter color (yellow, amber, orange…) insufficiently describes its blue light filtering characteristics
The most obvious characteristic of blue filters is their color: yellow, amber, orange, red, brown… But, for the purpose of reducing blue light induced problems, despite appearing similar in terms of their color appearance, different filters may have dramatically different absorption characteristics (The visual effects of intraocular colored filters; 2012).
For some filters (particularly sunglasses) there is no other information provided but % of Blue Light Transmission (BLT) and % of Visual Light Transmission (VLT/LT). For example in the image the Grey filter’s BLT is only 15%! But its VLT is also 15% such that it only makes things look darker, without selectively reducing the intensity of blue light reaching your retina more than other wavelengths. Conversely, Amber/Melanin filter lets trough 5 times more light than blue light.
If you have nothing else but these two figures, stick to the rule BLT < VLT.
More blue filters to choose from
There are many more blue filters available on the market than the ones featured above. Several more options with significant information about their transmission properties are available in these posts: computer work related blue filters, outdoors and driving (including polarized sunglasses).
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