High-energy visible light
In ophthalmology, high-energy visible light (HEV light) is high-frequency, high-energy light in the violet/blue band from 400 to 450 nm in the visible spectrum. Despite a lack of concurring scientific evidence, HEV light has sometimes been claimed to be a cause of age-related macular degeneration. Some sunglasses and beauty creams specifically block HEV, for added marketing value.
Blue-light hazard is defined as the potential for a photochemically-induced retinal injury resulting from electromagnetic radiation exposure at wavelengths primarily between 400 and 450 nm. This study has not been done in humans, only inconclusively in some rodent, primate, and in vitro studies. The mechanisms for photochemically-induced retinal injury are caused by the absorption of light by photoreceptors in the eye. Under normal conditions when light hits a photoreceptor, the cell bleaches and becomes useless until it has recovered through a metabolic process called the visual cycle.
Absorption of blue light, however, has been shown in rats and a susceptible strain of mice to cause a reversal of the process where cells become unbleached and responsive again to light before they are ready. At wavelengths of blue light below 430 nm this greatly increases the potential for oxidative damage. For blue-light circadian therapy, harm is minimized by employing blue light at the near-green end of the blue spectrum. "1-2 min of 408 nm and 25 minutes of 430 nm are sufficient to cause irreversible death of photoreceptors and lesions of the retinal pigment epithelium. ... The action spectrum of light-sensitive retinal ganglion cells was found to peak at approximately 450 nm, a range with lower damage potential, yet not completely outside the damaging range." A 2014 study found that LEDs cause retinal damage even in settings where they are used indirectly, such as household light bulbs.
An unpublished and non peer-reviewed 2013 in vitro study financed by skin care company Lipo Chemicals using shorter blue band spectrum LED lights claims that prolonged exposure may permanently damage the pigment epithelial cells of the retina. However, according to a specialist, the test conditions were the equivalent of staring at a blue light equivalent to a 100 watt incandescent source from 20 cm (8 in) for 12 hours, which is not deemed to be a realistic light exposure.. Sébastien Point and colleagues discussed in some recent peer-reviewed publications the validity of rodent models and conclude that LEDs are not a problem of public health in normal use but that caution must be taken for newborn infants, as their eye collect more light  and for specific occupational situations for which observers can look at high power leds for hours (for example LEDs quality control or alternative light therapies).
A recent study has given more insight about the Blue light hazard: permanent damage to the eye cells, as reported by a research made by a team from Toledo University , especially for children, who are big users of LED screen (smartphones,tablets...). However, the conclusion that LED technology would be more dangerous for retina than Tungsten lamp and fluorescent lamp is debated, as the LED spectrum does not contain potentially retinotoxic violet light (to which a child's lens is highly transparent) in contrary to spectra of fluorescent and incandescent lamps which are rich in violet light.
Blue light within the range 400-450 nm has been reported in a number of studies to be effective as local treatment of eczema and psoriasis, as it purportedly helps dampen the immune response. Recent studies have also shown improvement of facial acne upon exposure to a LED emitting at 414 nm. A combination of exposure to red and blue lights is used more and more in clinical dermatologic therapies. Constructors such as Philips currently develop devices and techniques emitting in the blue visible spectrum to be used in dermatologic therapy.
- Dykas, Carol (June 2004). "How to Protect Patients from Harmful Sunlight". www.2020mag.com.
- Glazer-Hockstein C, Dunaief JL (January 2006). "Could blue light-blocking lenses decrease the risk of age-related macular degeneration?". Retina (Philadelphia, Pa.). 26 (1): 1–4. doi:10.1097/00006982-200601000-00001. PMID 16395131.
- Margrain TH, Boulton M, Marshall J, Sliney DH (September 2004). "Do blue light filters confer protection against age-related macular degeneration?". Prog Retin Eye Res. 23 (5): 523–31. doi:10.1016/j.preteyeres.2004.05.001. PMID 15302349.
- ANSI/IESNA RP-27.1-05: Recommended Practice for Photobiological Safety for Lamp and Lamp Systems – General Requirements. American National Standard Institute/ Illuminating Engineering Society of North America. 10 June 2007. Archived from the original on 15 August 2007.
- Williams TP, Howell WL (March 1983). "Action spectrum of retinal light-damage in albino rats". Invest. Ophthalmol. Vis. Sci. 24 (3): 285–7. PMID 6832904. Archived from the original on 2012-05-25.
- Pautler EL, Morita M, Beezley D (May 1990). "Hemoprotein(s) mediate blue light damage in the retinal pigment epithelium". Photochem. Photobiol. 51 (5): 599–605. doi:10.1111/j.1751-1097.1990.tb01972.x. PMID 2367557.
- Grimm C, Wenzel A, Williams T, Rol P, Hafezi F, Remy C (February 2001). "Rhodopsin-mediated blue-light damage to the rat retina: effect of photoreversal of bleaching". Invest. Ophthalmol. Vis. Sci. 42 (2): 497–505. PMID 11157889. Archived from the original on 2012-05-25.
- Remy C. "Blue Light and the Retina: Good and Bad?". Soc Light Treatment Biol Rhythms. Abstracts 2005, 17:46.
- Lougheed, Tim (March 2014). "Hidden Blue Hazard? LED Lighting and Retinal Damage in Rats". Environmental Health Perspectives. 122 (3): A81. doi:10.1289/ehp.122-A81. PMC 3948029. PMID 24583823.
- LED lighting damages eyes, says Spanish investigator. thinkSPAIN (10 May 2013).
- Specialists question validity of LED eye damage study. ozgled.com (27 Oct 2015)
- S.Point, why you shouldn't be afraid of LEDs, European scientist https://www.europeanscientist.com/en/features/shouldnt-afraid-leds/
- S.Point and J. Lambrozo, some evidence that white LEDs are toxic for human at domestic radiance?, Radioprotection, September 2017 https://www.radioprotection.org/articles/radiopro/abs/2017/04/radiopro170025/radiopro170025.html
- S.Point, Blue Light Hazard: are exposure limit values protective enough for newborn infants, Radioprotection, July 2018
- S.Point and A. Barlier-Salsi, LEDs lighting and retinal damage, technical information sheets, SFRP, http://www.sfrp.asso.fr/medias/sfrp/documents/Divers/Fiche%20lampes%20%C3%A0%20Led%20SFRP%20-%20Anglais%20_%2006-2018%20(2).pdf
- S.Point, the danger of chromotherapy, Skeptical Inquirer, July/August 2017
- Weinstabl A, Hoff-Lesch S, Merk HF, von Felbert V (2011). "Prospective randomized study on the efficacy of blue light in the treatment of psoriasis vulgaris". Dermatology. 223: 251–9. doi:10.1159/000333364. PMID 22105015.CS1 maint: Multiple names: authors list (link)
- Pfaff S, Liebmann J, Born M, Merk HF, von Felbert V (2015). "Prospective Randomized Long-Term Study on the Efficacy and Safety of UV-Free Blue Light for Treating Mild Psoriasis Vulgaris". Dermatology. 231: 24–34. doi:10.1159/000430495. PMID 26044167.CS1 maint: Multiple names: authors list (link)
- Gold MH, Andriessen A, Biron J, Andriessen H (2009). "Clinical Efficacy of Self-applied Blue Light Therapy for Mild-to-Moderate Facial Acne". J Clin Aesthet Dermatol. 2: 44–50. PMC 2923954. PMID 20729943.CS1 maint: Multiple names: authors list (link)
- Morton CA, Scholefield RD, Whitehurst C, Birch J (2005). "An open study to determine the efficacy of blue light in the treatment of mild to moderate acne". J Dermatolog Treat. 16: 219–23. doi:10.1080/09546630500283664. PMID 16249142.CS1 maint: Multiple names: authors list (link)
- Wan MT, Lin JY (2014). "Current evidence and applications of photodynamic therapy in dermatology". Clin Cosmet Investig Dermatol. 7: 145–63. doi:10.2147/CCID.S35334. PMC 4038525. PMID 24899818.
- Nestor MS, Swenson N, Macri A, Manway M, Paparone P (2016). "Efficacy and Tolerability of a Combined 445nm and 630nm Over-the-counter Light Therapy Mask with and without Topical Salicylic Acid versus Topical Benzoyl Peroxide for the Treatment of Mild-to-moderate Acne Vulgaris". J Clin Aesthet Dermatol. 9: 25–35. PMC 4896818. PMID 27354885.CS1 maint: Multiple names: authors list (link)
- Hanlin, Pete (2004). "The Effects of Visible Light and UVR on the Visual System". Review of Optometry.
- "Artificial Lighting and the Blue Light Hazard (The Facts About Lighting and Vision)". MD Support Online Library.
- Koide R, Ueda TN, Dawson WW, et al. (October 2001). "[Retinal hazard from blue light emitting diode]". Nippon Ganka Gakkai Zasshi (in Japanese). 105 (10): 687–95. PMID 11692615.