LED Lighting, Screens and Health

Blue light affects circadian rhythms

As described in Normal eye responses to light, retina ipRGCs preferentially respond to blue light and inhibit the release of melatonin from the pineal gland in response to light. Signalling from ipRGCs, including the regulation of melatonin release, creates circadian rhythms. Too much exposure to artificial light at night, especially blue-enriched light, has been implicated in the alteration of circadian rhythms through suppression of melatonin release, although there is significant individual variability (reviewed in Chellappa, 2021). Light from LED bulbs and screens includes light in the blue portion of the spectrum, as does daylight and fluorescent light. Incandescent light also includes blue light, but it is less than produced by most LED light sources.

Early fluorescent tube lights tended to have greater flicker of blue light than other colors

There are not scientific reports specifically linking headaches or eyestrain to blue light from LEDs. However, it was reported to be helpful to block the blue light of early fluorescent lights because the flicker of those fluorescent lights is greatest in the blue range of the spectrum. Partially blocking the blue light flicker of fluorescent lights with magnetic ballasts using eyeglasses tinted with the pigment FL-41 was helpful to some patients with photophobia (Wilkins & Wilkinson, 1991). Wilkins and Wilkinson designed the FL-41 lens filter to block the transmission of about 90% of light in the blue to green range (400 nm to 550 nm), not because the color (wavelength) of blue light is harmful, but rather because the flicker of the fluorescent lights happened to be greatest in the blue range. They designed the FL-41 tint specifically to reduce the visibility of flicker from warm white and cool white (halophosphate) fluorescent lights, rather than choosing this filter because light of a blue color is generally harmful. 

In fluorescent tube lights, an arc of current excites gas in the tube to emit ultraviolet light which then causes phosphors on the inner surface to fluoresce, producing visible light. The current fluctuates rapidly at the mains AC frequency (100 Hz or 120 Hz), causing the UV light emission to flicker. Phosphors continue to glow for a brief period of time after their excitation stops, creating a partial afterglow in the dim phase of the light flicker. In the phosphorescent coatings of the magnetically ballasted fluorescent tube lights that were common at the time of the development of the FL-41 lens, the phosphors that emitted non-blue colors happened to glow for a longer time than the phosphors that emitted blue light. The non-blue phosphors were still glowing when they were next excited. The more rapid loss of blue light phosphorescence in the dim phase of the current fluctuation created more visible blue light flicker than the flicker of other colors (Brundrett, 1974). Thus, FL-41 lenses reduce the visibility of fluorescent light flicker from fluorescent tubes using old halophosphate phosphors specifically by reducing the transmission of blue light by 90%. They would not be predicted to significantly reduce the visibility of LED light flicker because the LED light diodes have faster response times to changes in current than fluorescent lights and because the phosphors that coat the inner surface of some types of modern LED lights have faster decay rates than the old halophosphate phosphors that were previously used in fluorescent lights (Wilkins, 2021). So FL-41 lenses, while reducing the brightness of some wavelengths of LED light, would not reduce the flicker of LED light that reaches the eye. 

The article TFT Central: Pulse Width Modification, 2015 compares the flicker of the separate red, green, and blue color channels for CCFL LCD monitors and LED LCD monitors, showing that the blue light flicker is out of sync with the red and green flicker for CCFL backlit monitors while the flicker of the three color channels are synchronous for LED backlit monitors. This further shows that the flicker from LEDs is not related to the color.

A lack of evidence that blue light blocking lenses prevent symptoms from computer use

Although blue light has been suggested as a possible cause of computer vision syndrome (also called "digital eyestrain" or "visual fatigue", see Survey: Discussion) by manufacturers of these lenses and in popular culture, recent research has not provided evidence that blue light causes adverse health effects (reviewed in Sheppard & Wolffsohn, 2018). The utility of wearing blue light blocking glasses has not been established by research, with multiple limited studies showing a lack of an effect and another study indicating that some wraparound-style lenses might be helpful because they reduce tear evaporation rather than because they block blue light (reviewed in Sheppard & Wolffsohn, 2018). A call has been made for the need for a well-controlled, large-scale study to address whether blue light blocking lenses are helpful to prevent eyestrain or visual fatigue (Lawrenson et al., 2017). An additional recent analysis also indicates that there is not evidence that blue light blocking lenses are helpful for a variety of conditions, including eyestrain (Vagge et al., 2021).

Brundrett, G. W. Human sensitivity to flicker. Lighting Research & Technology. 6, 127-143 (1974). https://journals.sagepub.com/doi/abs/10.1177/096032717400600302?journalCode=lrtb

Chellappa SL. Individual differences in light sensitivity affect sleep and circadian rhythms. Sleep. 2021 Feb 12;44(2):zsaa214. https://doi.org/10.1093/sleep/zsaa214

Lawrenson JG, Hull CC, Downie LE. The effect of blue-light blocking spectacle lenses on visual performance, macular health and the sleep-wake cycle: a systematic review of the literature. Ophthalmic Physiol Opt. 2017 Nov;37(6):644-654. https://doi.org/10.1111/opo.12406

Sheppard AL, Wolffsohn JS. Digital eye strain: prevalence, measurement and amelioration. BMJ Open Ophthalmol. 2018;3(1):e000146. Published 2018 Apr 16. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6020759/pdf/bmjophth-2018-000146.pdf

Vagge A, Ferro Desideri L, Del Noce C, Di Mola I, Sindaco D, Traverso CE. Blue light filtering ophthalmic lenses: A systematic review. Semin Ophthalmol. 2021 Oct 3;36(7):541-548. https://doi.org/10.1080/08820538.2021.1900283

WIlkins, A. Fear of light: On the cause and remediation of photophobia. Lighting Research & Technology. 53, 395-404 (2021). https://doi.org/10.1177%2F1477153521998415

Wilkins, A.J. & Wilkinson, P. A tint to reduce eye-strain from fluorescent lighting? Preliminary observations. Ophthalmic & Physiological Optics. 11, 172-175 (1991). https://doi.org/10.1111/j.1475-1313.1991.tb00217.x