Understanding blue light: Making sense of the spectrum

Image credit: AdobeStock/Maria Mikhaylichenko/AI

Blue light, a part of the visible light spectrum, is naturally present in sunlight and is emitted by electronic devices such as computers, smartphones, tablets, and LED lighting.There has been significant discussion in the media about the importance of blue light for our circadian rhythm and mood regulation, and that excessive exposure could be linked to various eye problems. What do clinical optometrists and ophthalmologists need to know when discussing blue light–blocking ophthalmic lenses with our patients?

Your patient requests lenses with a “blue-blocking tint.” You’ve heard that blue light can be harmful, potentially contributing to the development of age-related macular degeneration (AMD) and disrupting sleep. But you’ve also heard that exposure to full-spectrum lighting, including blue, can be protective for myopia progression in children.

So what do you order? What does the lens manufacturer provide? And how do you verify it?

To help answer some of these questions, the Accredited Standards Committee Z80, part of the American National Standards Institute, established an ad hoc subcommittee, the Spectral Bands Task Force (SBTF), in April 2021. After more than 2 years of work, discussion, and debate among leaders and experts from industry and academia, consensus was reached on the creation of a uniform and consistent classification system defining high-energy visible (HEV) radiation. Details of this system can be found in the final report of the SBTF, available for free from The Vision Council,¹ and in an April 2024 editorial published in Optometry and Vision Science.²

As a brief overview, the SBTF system divides blue light into 3 sub-bands: HEV 3 (380-400 nm), HEV 2 (400-455 nm), and HEV 1 (455-500 nm). The greatest consensus was regarding HEV 3, where the near end of the UV spectrum and the far end (violet) of the visible spectrum overlap. International standards and eye safety experts have long argued that UV protection should extend to 400 nm, which is what most premium sunglasses and UV-protective safety eyewear provide. However, the ophthalmic industry prefers a cutoff at 380 nm because most tints and coatings in ophthalmic dress lenses that fully block all wavelengths shorter than 400 nm would cause a clear lens to have a cosmetically unacceptable yellow hue.

The remaining 100-nm zone, from 400 to 500 nm, was divided into 2 sub-bands that adequately differentiate portions of the spectrum that have been implicated in exacerbating retinal disease, such as AMD (ie, below 455 nm), versus that which could disrupt sleep and upset an individual’s circadian rhythm, which lies above 455 nm. With continued research and further understanding of ocular effects of chronic as well as acute exposure, the separation of these sub-bands, as well as justification for their use, can change over time.

Although the classification system acknowledges the distinctions of the 3 sub-bands, it does not provide guidelines or recommendations as to how they should be applied; that decision is still up to the doctor and patient. What the system does recommend is for a lens manufacturer who claims blue blocking to clearly identify which sub-band(s), HEV 1, 2, and/or 3, are being blocked, and, by way of providing the full transmittance spectrum, to what extent. In this way, products from different manufacturers can easily be compared to determine whether they meet the patient’s needs. Keep in mind that not all “blues” are the same.

Conclusion

It is important for optometrists to understand the classification system defining HEV radiation when discussing blue-blocking tint options with our patients. HEV light–filtering spectacle lenses have variable transmission properties of both UV-A and HEV light.³ The Spectral Bands Task Force classification is an important milestone for the optometric profession in educating our patients and helping them make decisions that meet their visual and eye health needs.

References:

1. Accredited Standards Committee for Ophthalmic Optics. Z80 Spectral Bands Task Force Technical Report. November 2023. Accessed September 6, 2024. https://thevisioncouncil.org/sites/default/files/assets/media/ASC%20Z80%20SBTF%20Technical%20Report%20FINAL%2029NOV2023.pdf

2. Zimmerman AB, Yuhas PT, Citek K. Letter to the editor: The Spectral Bands Task Force: a consensus on the representation of high-energy visible radiation. Optom Vis Sci. 2024:101(4);176-178. doi:10.1097/opx.0000000000002124

3. Rampersad N, Carlson A. Spectral transmission of commercially available high-energy visible light–filtering spectacle lenses. Optom Vis Sci. 2024;101(8):508-513. doi:10.1097/OPX.0000000000002171