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What is FL-41 and How Does It Improve Light Sensitivity?

What is FL-41 and How Does It Improve Light Sensitivity?

Written by Greg Bullock on 3rd Oct 2018

FL-41 has been around for decades and is supported by medical research as a key tool in the fight against light sensitivity and photophobia. In this post, we answer some of the biggest questions patients have about how and why it works.

What is FL-41?

FL-41 is a type of specialty eyewear tint designed for people with light sensitivity and most commonly recommended for patients with migraine, post-concussion syndrome and dozens of other light-sensitive conditions. It was first introduced back in the early 1990’s as part of a research study that explored how glasses coated with this precision tint might help alleviate the migraine symptoms of young children—particularly against the harm of fluorescent lighting. Within the last decade, advancements in the understanding of photophobia and light sensitivity have precipitated more widespread availability of FL-41 to patients all over the world.

How Does FL-41 Work?

Glasses lenses that are properly tinted with FL-41 block a majority of blue light—approximately 80 percent—within the spectrum of 480-520 nanometers (nm). Why that particular light? It stems from clinical research that showed that those particular wavelengths were the most likely to trigger or aggravate light sensitivity in conditions like migraine. Not only can exposure to this light hurt the eyes and brain of a vulnerable patient, but it can also bring on other symptoms of their illness—dizziness or vertigo, nausea, anxiety and more.1

FL-41 Glasses Tint Infographic

Similarly, conventional fluorescent lighting can emit an invisible “flicker” or modulation at certain wavelengths that can cause problems for sensitive brains. FL-41 stunts much of this flicker to provide relief under artificial fluorescents and even device screens that produce a similar effect.2

Who Benefits from FL-41?

Although FL-41 was developed primarily for people with migraine-related light sensitivity, you do not need only have a headache disorder to feel relief with the tint. In fact, more than 50 known conditions are associated with photophobia and persistent light sensitivity. Not to mention that eye and head injuries, attention deficit issues, as well as some forms of epilepsy can also be affected by light. In addition, anybody who generally feels badly under artificial fluorescents or staring at digital screens all day can enjoy the positive results of FL-41.

FL-41 Glasses vs Regular Sunglasses

As we mentioned FL-41 glasses only target blue light, which makes them the preferred substitute for indoor use over regular, dark sunglasses. FL-41 lenses tinted for indoors do not have to be nearly as dark and therefore do not risk the additional complications of ocular dark adaptation and social isolation. However, FL-41 can separately be applied to a darker and polarized lens, making them the best sunglasses you could ever own.

Man and Woman wearing FL-41 Tint on Glasses
FL-41 can be made with lighter indoor lenses (pictured left) or darker, polarized outdoor lenses (pictured right).

What Research Supports FL-41?

Two landmark studies have verified the benefits of the FL-41 tint for patients. As noted above, the originating study showed that migraine frequency in children decreased from 6 attacks per month to fewer than two per month. Perhaps most importantly, the use of FL-41 sustained this improvement over time when compared with a simple blue tint.3 A 2016 study applied the same FL-41 properties through a different mechanism, but ultimately validated the earlier research.4

A more recent study focused on those with sensitivity to light stemming from benign essential blepharospasm. Once again, the wearing of FL-41 glasses created superior outcomes for participants versus other therapeutic tints; not only did they help reduce generalized photophobia, but they minimized fluorescent light sensitivity and overall condition and symptom burden.5

Related Reading: How FL-41 Compared With Other Tinted Lenses ➜

Although not considered direct research, it is also important to note that thousands of individuals have tried and benefitted from FL-41 eyewear. And hundreds more specialists in headache/migraine medicine and neurology refer the tint to their patients.

Where Can You Buy FL-41?

TheraSpecs are the leading brand of FL-41 glasses, with thousands of customers vouching for their quality and effectiveness. Whether you need prescription or non prescription lenses, enhanced frame protection or anything else, the TheraSpecs team is here to help. Click below to start shopping for FL-41 today!


1M. Tatsumoto, T. Eda, T. Ishikawa, M. Ayama, K. Hirata “Light of Intrinsically Photosensitive Retinal Ganglion Cell (ipRGC) Causing Migraine Headache Exacerbation.” IHC symposium OR3. 2013 June.

2Wilkins AJ, Wilkinson P. “A tint to reduce eye strain from fluorescent lighting? Preliminary observations.” Ophthalmic Physiol Opt. 1991 Apr;11(2):172-5.

3Good PA, Taylor RH, Mortimer MJ. “The use of tinted glasses in childhood migraine.” Headache. 1991 Sep;31(8):533-6.

4Hoggan RN, Subhash A, Blair S, et al. Thin-film optical notch filter spectacle coatings for the treatment of migraine and photophobia. Journal of clinical neuroscience : official journal of the Neurosurgical Society of Australasia. 2016;28:71-76. doi:10.1016/j.jocn.2015.09.024.

5Blackburn MK, Lamb RD, Digre KB, et al. FL-41 Tint Improves Blink Frequency, Light Sensitivity, and Functional Limitations in Patients with Benign Essential Blepharospasm. Ophthalmology. 2009;116(5):997-1001. doi:10.1016/j.ophtha.2008.12.031.

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